Intrusive Rocks of the Holden and 

Lucerne Quadrangles, Washington 

The Relation of Depth Zones, Composition, 

Textures, and Emplacement of Plutons

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1220
Intrusive Rocks of the Holden and 

Lucerne Quadrangles, Washington 

The Relation of Depth Zones, Composition, 

Textures, and Emplacement of Plutons

By FRED W. CATER

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1220

A study of intrusive rocks 

ranging in age from 

Tnassic to Miocene 

and in depth zones from 

subvolcamc to catazone

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1982
UNITED STATES DEPARTMENT OF THE INTERIOR 

JAMES G. WATT, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Cater, Frederick William, 1912-

Intrusive rocks of the Holden and Lucerne Quadrangles, Washington.

(Geological Survey Professional Paper 1220)

Bibliography: 108 p.

Supt. of Docs. No.: 119.16

1. Intrusions (Geology) Washington (State) Chelan Co. 2. Geology, Stratigrapnic Cenozoie. 3. Geology, Stratigraphic Mesozoic.

I. Title. II. Series: United States Geological Survey Professional Paper 1220.

QE6I1.5.U6C37 551.8'8'0979759 80-607844

For sale by the Branch of Distribution, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Page

Abstract ------------------------------------------------- 1

Introduction --------------------------------------------- 3

Acknowledgments ------------------------------------ 3

Previous work ---------------------------------------- 3

Tectonic setting ------------------------------------------ 3

Preintrusive rocks ---------------------------------------- 4

Swakane Biotite Gneiss .-.--. r -----------------------~ 5

Late Paleozoic metamorphic rocks --------------------- 6

Pre-Tertiary intrusive rocks ------------------------------- 7

Ultramafic rocks ------------------------------------- 7

Dumbell Mountain plutons --------------------------- 8

Hornblende-quartz diorite gneiss ------------------- H

Hornblende-quartz diorite augen gneiss ------------ 17

Gneissic hornblende-quartz diorite ----------------- 17

Bearcat Ridge plutons -------------------------------- 18

Leroy Creek pluton ----------------------------------- 20

Seven-fingered Jack and Entiat plutons ---------------- 23

Biotite-hornblende-quartz diorite ------------------ 24

Hornblende-biotite-quartz diorite ------------------ 25

Hornblende-quartz diorite gneiss ------------------- 26

Hornblende diorite and gabbro -------------------- 26

Contact complexes ------------------------------- 27

Leucocratic quartz diorite and granodiorite ------------- 28

Tenpeak and White Mountain plutons ----------------- 31

Hornblende-biotite-quartz diorite and quartz diorite

gneiss ----------------------------------------- 33

Flaser gneiss --------------------------------- 33

Interlayered zone unit ------------------------ 34

Contact complexes --------------------------- 34

Petrography --------------------------------- 34

Sulphur Mountain pluton ----------------------------- 35

High Pass and Buck Creek plutons -------------------- 37

Riddle Peaks pluton---------------------------------- 40

Cardinal Peak pluton --------------------------------- 46

Hornblende-biotite-quartz diorite and biotite granodiorite ------------------------------------ f - - - - 47

Calcic hornblende diorite and quartz diorite -------- 48

Contact complexes ------------------------------- 49

Petrography ------------------------------------- 50

Tertiary intrusive rocks ----------------------------------- 53

Early Eocene intrusive rocks -------------------------- 53

	Page

Tertiary intrusive rocks Continued

Early Eocene intrusive rocks Continued

Clark Mountain stocks ---------------------------- 53

Late Eocene intrusive rocks --------------------------- 54

Mineralogy -------------------------------------- 56

Textures ----------------------------------------- 57

Analytical data ---------------------------------- 58

Description of rocks ------------------------------ 58

Dikes ------------------------------------------- 58

Pawdite ------------------------------------- 58

Kersantite ----------------------------------- 59

Augite minette ------------------------------- 59

Spessartite----------------------------------- 59

Other fine-grained, dark dikes ----------------- 60

Hornblende diorite of upper Rock Creek -------- 60

Granitoid dikes ------------------------------ 60

Duncan Hill pluton ------------------------------- 61

Larch Lakes pluton ------------------------------- 68

Rampart Mountain pluton ------------------------ 70

Old Gib volcanic rocks and associated dacite porphyry 72

Jointing in volcanic neck --------------------- 74

Intrusive breccia --------------------------------- 75

Hornblende-biotite-quartz diorite ------------------ 75

Railroad Creek pluton and associated rocks --------- 77

Copper Peak and Holden Lake plutons ------------- 80

Biotite-quartz monzonite and granodiorite ---------- 82

Post-late Eocene intrusive rocks ----------------------- 84

Dikes of biotite dacite and rhyodacite ------------- 84

Rhyodacite ---------------------------------- 84

Dacite and rhyodacite dikes ------------------- 85

Miocene intrusive rocks ------------------------------- 86

Cloudy Pass batholith and related rocks ----------- 86

Chilled border rocks -------------------------- 87

Leucocratic biotite-quartz monzonite --------------- 89

Contact complexes --------------------------------------- 90

General geologic problems relating to the intrusive rocks - - - - 91

Relation of intrusives to host rocks and the room problem 92

Ages of intrusive rocks and related problems ----------- 93

Composition and differentiation ----------------------- 96

Textures and depth zones ----------------------------- 101

References ----------------------------------------------- 102

ILLUSTRATIONS

FIGURE 1. Index map of Washington showing physiographic provinces and locations of Holden and Lucerne quadrangles ------

2. Map showing locations of the plutons in the Holden and Lucerne quadrangles -----------------------------------

3. Triangular diagram showing modal rock classification system used in this report ---------------------------------

4. Tectonic sketch map of north-central Washington showing the relation of the Holden and Lucerne quadrangles to 

the tectonic framework ------------------------------------------------------------------------------------

5. Photograph of interlayered late Paleozoic quartzite, biotite schist, and hornblende gneiss, upper Klone Creek, Lucerne 

quadrangle -----------------------------------------------------------------------------------------------

m
IV CONTENTS

Page

FIGURE 6. Photograph of gabbroic orbicules in peridotite from Holden mine, Holden quadrangle ---------------------------- 8

7. Photograph of Dumbell Mountain hornblende-quartz diorite augen gneiss containing inclusions with mafic margins - 9

8. Photomicrograph of gneissic hornblende-quartz diorite from the Dumbell Mountain plutons ----------------------- 10

9. Photomicrograph of oscillatory- and patchy-zoned andesine in hornblende-quartz diorite gneiss from the Dumbell Mountain plutons ---------------------------------------------------------------------------------------------- 11

10. Map showing location of modally analyzed samples from the Dumbell Mountain plutons ------------------------- 12

11. Triangular diagram showing plot of modes of rock samples from Dumbell Mountain plutons ---------------------- 15

12. Triangular diagram showing plot of norms of rock samples from the Dumbell Mountain, Bearcat Ridge, and Leroy

Creek plutons -------------------------------------------------------------------------------------------- 15

13. Variation diagrams of major oxides in analyzed rock samples from pre-Tertiary plutons -------------------------- 16

14-18. Photographs of:

14. Hornblende-quartz diorite gneiss from the Dumbell Mountain plutons ------------------------------------- 17

15. Gneissic hornblende-quartz diorite, a less gneissic facies, from the Dumbell Mountain plutons --------------- 18

16. Protoclastic biotite-hornblende-quartz diorite gneiss from the Bearcat Ridge plutons ------------------------ 18

17. Hornblende-biotite granodiorite gneiss from the Bearcat Ridge plutons ------------------------------------- 19

18. Biotite granodiorite from the Bearcat Ridge plutons ------------------------------------------------------ 19

19. Map showing location of modally analyzed samples from the Bearcat Ridge plutons ----------------------------- 21

20. Triangular diagram showing plot of modes of rock samples from Bearcat Ridge plutons -------------------------- 22

21. Photograph of gneissic biotite-quartz diorite from the Leroy Creek pluton --------------------------------------- 22

22. Map showing location of modally analyzed samples of biotite-quartz diorite gneiss from the Leroy Creek pluton - - - - 24

23. Triangular diagram showing plot of modes of biotite-quartz diorite gneiss samples from the Leroy Creek pluton ---- 24 

24-27. Photographs of:

24. Coarse- and medium-grained hornblende gabbro from contact complex of Entiat pluton ------------------ 25

25. Contact complex of Entiat pluton showing pegmatitic hornblende gabbro, schist, and hornblendite -------- 25

26. Biotite-hornblende-quartz diorite from the Seven-fingered Jack pluton ---------------------------------- 26

27. Biotite-hornblende-quartz diorite from the Seven-fingered Jack pluton, showing strong lineation defined by

pencils of mafic-rich material ---------------------------------------------------------------------- 26

28. Photomicrograph of protoclastic hornblende-biotite-quartz diorite from Seven-fingered Jack pluton showing cracks in

fractured crystal of andesine filled with biotite, orthoclase, and quartz ---------------------------------------- 27

29. Photograph of hornblende-biotite-quartz diorite from the Entiat pluton ----------------------------------------- 27

30. Photograph of hornblende-biotite quartz diorite gneiss from the Entiat pluton ----------------------------------- 27

31. Photograph of rotated inclusions of late Paleozoic gneiss in hornblende-quartz diorite gneiss from the Entiat pluton 28

32. Photomicrograph of hypidiomorphic and protoclastic hornblende-quartz diorite gneiss from the Entiat pluton ------ 28

33. Photograph of contact complex of the Entiat pluton showing gabbro chilled against quartz diorite ----------------- 29

34. Map showing location of modally analyzed samples from the Seven-fingered Jack and Entiat plutons ------------- 29

35. Triangular diagram showing plot of modes of rock samples from Seven-fingered Jack and Entiat plutons ---------- 31

36. Triangular diagram showing plot of norms of leucocratic quartz diorite and granodiorite samples and rock samples from

the Seven-fingered Jack and Entiat plutons ----------------------------------------------------------------- 32

37-40. Photographs of:

37. Migmatite of leucocratic quartz diorite in biotite-hornblende-quartz diorite of the Seven-fingered Jack pluton 32

38. Leucocratic quartz diorite ---------------------------------------------------------------------------- 32

39. Hornblende-biotite-quartz diorite from the Tenpeak pluton --------------------------------------------- 34

40. Interlayered biotite-hornblende-quartz diorite gneiss and hornblende schist of the interlayered unit of the Tenpeak pluton -------------------------------------------------------------------------------------- 34

41. Photomicrograph of intergrowth of clinozoisite-epidote and quartz resembling myremekite, quartz diorite from the

Tenpeak pluton ------------------------------------------------------------------------------------------ 35

42. Map showing location of modally analyzed samples from the Tenpeak and White Mountain plutons --------------- 36

43. Triangular diagram showing plot of modes of quartz diorite and quartz diorite gneiss samples from the Tenpeak and

White Mountain plutons ---------------------------------------------------------------------------------- 36

44. Triangular diagram showing plot of norms of rock samples from the Tenpeak, White Mountain, Cardinal Peak, and

High Pass plutons ---------------------------------------------------------------------------------------- 37

45. Photograph of gneissic granodiorite from the Sulphur Mountain pluton ----------------------------------------- 37

46. Triangular diagram showing plot of modes of hornblende-biotite granodiorite samples from the Sulphur Mountain

pluton --------------------------------------------------------------------------------------------------- 38

47-50. Photographs of:

47. Granodiorite from the High Pass pluton -------------------------------------------------------------- 38

48. Foliated granodiorite from the High Pass pluton ------------------------------------------------------- 38

49. Granodiorite of the High Pass pluton in the core of an antiform in upper Paleozoic metasedimentary rocks - 39

50. Contact of granodiorite of the High Pass pluton and hornblende schist ---------------------------------- 40

51. Map showing locations of modally analyzed samples of biotite-quartz diorite and granodiorite from the High Pass and

Buck Creek plutons--------------------------------------------------------------------------------------- 41

52. Triangular diagram showing plot of modes of biotite-quartz diorite and granodiorite samples from the High Pass pluton 41
CONTENTS V

Page

FIGURES 53-56. Photographs of:

53. Layered hornblende grabbro of the Riddle Peaks pluton and septum of gneiss in Riddle Peaks ------------ 41

54. Hornblende gabbro from the Riddle Peaks pluton ------------------------------------------------------ 42

55. Contorted layers in gabbro of the Riddle Peaks pluton ------------------------------------------------- 42

56. Layered gabbro from the Riddle Peaks pluton --------------------------------------------------------- 42

57. Photomicrograph of gabbro from the Riddle Peaks pluton showing poikilitic crystals of bytownite that have grown around

hornblende ----------------------------------------------------------------------------------------------- 44

58. Photomicrograph showing chlorite having helminth structure in gabbro of the Riddle Peaks pluton ---------------- 44

59. Map showing location of modally analyzed samples of gabbro from the Riddle Peaks pluton ---------------------- 46

60-64. Photographs of:

60. Foliated hornblende-biotite-quartz diorite from the Cardinal Peak pluton -------------------------------- 47

61. Quartz diorite from the Cardinal Peak pluton, showing a pseudoporphyritic appearance resulting from extreme

protoclasis ---------------------------------------------------------------------------------------- 48

62. Biotite granodiorite from the Cardinal Peak pluton, showing only slight flaser texture -------------------- 48

63. Contact complex of Cardinal Peak pluton, consisting largely of gabbro ---------------------------------- 49

64. Contact complex of Cardinal Peak pluton showing inclusions of metamorphic rocks, gabbro, and hornblendite in

a matrix of quartz diorite -------------------------------------------------------------------------- 49

65. Map showing location of modally analyzed samples of quartz diorite and granodiorite from the Cardinal Peak

pluton --------------------------------------------------------------------------------------------------- 52

66. Triangular diagram showing plot of modes of diorite, quartz diorite, and granodiorite samples from the Cardinal Peak

pluton --------------------------------------------------------------------------------------------------- 52

67. Photograph of hornblende-biotite granodiorite from the Clark Mountain stocks ---------------------------------- 53

68. Map showing location of modally analyzed samples of biotite-quartz diorite and granodiorite of the Clark Mountain

stocks --------------------------------------------------------------------------------------------------- 55

69. Triangular diagram showing plot of modes of biotite-quartz diorite and granodiorite samples from the Clark Mountain

stocks --------------------------------------------------------------------------------------------------- 55

70. Variation diagram of major oxides in rock samples from Eocene plutons ---------------------------------------- 55

71. Triangular diagram showing plot of norms of samples from small Tertiary intrusives ----------------------------- 56

72-75. Photographs of:

72. Marble-cake mixture of biotite-quartz diorite and granodiorite in Duncan Hill pluton at Fern Lake -------- 61

73. Protoclastic hornblende-biotite-quartz diorite near north end of Duncan Hill pluton ---------------------- 62

74. Biotite granodiorite from the Duncan Hill pluton at the south edge of the Lucerne quadrangle ------------ 64

75. Miarolytic biotite-quartz monzonite from the Duncan Hill pluton on Stormy Mountain ------------------- 64

76. Map showing location of chemically and modally analyzed samples of Duncan Hill, Larch Lakes, and Rampart Mountain

plutons -------------------------------------------------------------------------------------------------- 68

77. Triangular diagram showing plot of modes of rock samples from the Duncan Hill pluton ------------------------- 69

78. Variation diagram of major oxides in samples from the Duncan Hill pluton ------------------------------------- 69

79. Triangular diagram showing plot of norms of rock samples from the Duncan Hill pluton, and isobaric lines marking the position of the quartz-feldspar boundary at various water pressures ------------------------------------ 70

80. Photograph of biotite granodiorite from the Larch Lakes pluton ------------------------------------------------ 70

81. Triangular diagram showing plot of modes of rock samples from the Larch Lakes and Rampart Mountain plutons-- 71 

82-86. Photographs of:

82. Biotite-quartz monzonite from the Rampart Mountain pluton ------------------------------------------- 71

83. Columnar joints in Old Gib volcanic neck and crosscutting basaltic dike -------------------------------- 73

84. Vertical sheeting in Pelean spine in Old Gib volcanic neck --------------------------------------------- 73

85. Intermixed hornblende-biotite-quartz diorite, biotite-quartz monzonite, and inclusions of biotite schist, showing various stages of alteration, at the Holden mine -------------------------------------------------- 75

86. Hornblende-biotite-quartz diorite --------------------------------------------------------------------- 75

87. Triangular diagram showing plot of modes of hornblende-biotite-quartz diorite samples --------------------------- 77

88. Map showing location of modally analyzed samples from Eocene plutons ---------------------------------------- 73

89. Photograph of biotite granodiorite from the Railroad Creek pluton ---------------------------------------------- 73

90. Photograph of porphyritic biotite-quartz diorite dike rock from the Railroad Creek pluton ------------------------ 79

91. Triangular diagram showing plot of modes of granodiorite and quartz diorite samples from the Railroad Creek pluton 80

92. Photograph of hornblende-quartz gabbro cut by biotite-quartz monzonite from the Holden Lake pluton------------ 81

93. Triangular diagram showing plot of modes of hornblende-quartz gabbro samples from the Copper Peak and Holden

Lake plutons --------------------------------------------------------------------------------------------- 82

94. Photograph of biotite-quartz monzonite ----------------------------------------------------------------------- 83

95. Triangular diagram showing plot of modes of biotite-quartz monzonite and granodiorite samples ------------------ 85

96. Map showing locations of modally analyzed samples of granodiorite from the Cloudy Pass batholith--------------- 88

97. Triangular diagram showing plot of modes of granodiorite samples from the Cloudy Pass batholith ---------------- 88

98. Diagram showing variation in contents of Si02 , K2 0, Na2 0, and CaO along the length of the Duncan Hill pluton - - 99
VI CONTENTS

TABLES

Page

TABLE 1. Chemical and spectrographic analyses of a composite sample of Swakane Biotite Gneiss ----------------------------- 6

2. Modal analyses of samples of hornblende-quartz diorite and hornblende-quartz diorite gneiss from the Dumbell Mountain

plutons --------------------------------------------------------.------------------------- ------------------- 13

3. Chemical and spectrographic analyses and norms of rock samples from the Dumbell Mountain plutons --------------- 14

4. Modal analyses of samples of quartz diorite and granodiorite gneiss from the Bearcat Ridge plutons ------------------ 20

5. Chemical and spectrographic analyses and norms of rock samples from the Bearcat Ridge plutons ------------------- 21

6. Modal analyses of samples of biotite-quartz diorite gneiss from the Leroy Creek pluton------------------------------ 23

7. Chemical and spectrographic analyses and norms of a composite sample of biotite-quartz diorite from the Leroy Creek

pluton ------------------------------------------------------------------------------------------------------ 23

8. Modal analyses of samples of diorite, gabbro, quartz diorite, and quartz diorite gneiss from the Seven-fingered Jack and

Entiat plutons----------------------------------------------------------------------------------------------- 30

9. Chemical and spectrographic analyses and norms of rock samples from the Seven-fingered Jack and Entiat plutons - - - 31

10. Chemical and spectrographic analyses and norms of samples of leucocratic quartz diorite and granodiorite ------------ 33

11. Modal analyses of samples of quartz diorite and quartz diorite gneiss from the Tenpeak and White Mountain plutons - 35

12. Chemical and spectrographic analyses and norms of composite rock samples from the Tenpeak and White Mountain plutons 36

13. Modal analyses of samples of hornblende-biotite granodiorite from the Sulphur Mountain pluton --------------------- 38

14. Modal analyses of samples of biotite-quartz diorite and granodiorite from the High Pass pluton ---------------------- 40

15. Chemical and spectrographic analyses and norms of a composite sample of biotite-quartz diorite from the High Pass pluton 41

16. Modal analyses of samples of hornblende gabbro from the Riddle Peaks pluton ------------------------------------- 46

17. Chemical and spectrographic analyses of a composite sample of hornblende gabbro from the Riddle Peaks pluton ----- 47

18. Modal analyses of samples of diorite, quartz diorite, and granodiorite from the Cardinal Peak pluton----------------- 51

19. Chemical and spectrographic analyses and norms of composite samples of rocks from the Cardinal Peak pluton ------- 52

20. Modal analyses of samples of biotite-quartz diorite and granodiorite from the Clark Mountain stocks ----------------- 54

21. Chemical and spectrographic analyses and norms of a composite sample of biotite granodiorite from the Clark Mountain

stocks ------------------------------------------------------------------------------------------------------ 54

22. Modal analyses of samples of biotite- and homblende-biotite-quartz diorite and granodiorite from the Duncan Hill pluton 6 \

23. Chemical and spectrographic analyses and norms of rocks from the Duncan Hill pluton ----------------------------- 66

24. Modal analyses of samples of granodiorite from the Larch Lakes pluton -------------------------------------------- 70

25. Chemical and spectrographic analyses and norms of a composite sample of biotite granodiorite from the Larch Lakes pluton 71

26. Modal analyses of samples of quartz monzonite from the Rampart Mountain pluton -------------------------------- 72

27. Chemical and spectrographic analyses and norms of a composite sample of biotite-quartz monzonite from the Rampart

Mountain pluton -------------------------------------------------------------------------------------------- 73

28. Chemical and spectrographic analyses and norms of a composite sample of dacite from the Old Gib volcanic neck - - - - 74

29. Modal analyses of samples of late Eocene hornblende-biotite-quartz diorite ----------------------------------------- 76

30. Chemical and spectrographic analyses and norms of a composite sample of late Eocene hornblende-biotite-quartz diorite 77

31. Modal analyses of samples of granodiorite and quartz monzonite from the Railroad Creek pluton -------------------- 80

32. Chemical and spectrographic analyses and norms of a composite sample of biotite granodiorite from the Railroad Creek

pluton ------------------------------------------------------------------------------------------------------ 80

33. Modal analyses of samples of hornblende-quartz gabbro from the Copper Peak and Holden Lake plutons ------------- 82

34. Chemical and spectrographic analyses and norms of quartz gabbro from the Holden Lake pluton--------------------- 82

35. Modal analyses of samples of biotite-quartz monzonite and granodiorite of post-late Eocene age --------------------- 84

36. Chemical and spectrographic analyses and norms of a composite sample of biotite-quartz monzonite ----------------- 85

37. Modal analyses of samples of granodiorite from the Cloudy Pass batholith ----------------------------------------- 88

38. Initial strontium isotope ratios of gabbro and quartz diorite from intrusive complexes associated with the Seven-fingered

Jack plutons ------------------------------------------------------------------------------------------------ 92

39. Radiometric ages of intrusive rocks ------------------------------------------------------------------------------ 94
INTRUSIVE ROCKS OF THE HOLDEN AND 

LUCERNE QUADRANGLES, WASHINGTON 

THE RELATION OF DEPTH ZONES, COMPOSITION, 

TEXTURES, AND EMPLACEMENT OF PLUTONS

By FRED W. CATER

ABSTRACT

The core of the northern Cascade Range in Washington consists of 

Precambrian and upper Paleozoic metamorphic rocks cut by numerous 

plutons, ranging in age from early Triassic to Miocene. The older 

plutons have been eroded to catazonal depths, whereas subvolcanic 

rocks are exposed in the youngest plutons. The Holden and Lucerne 

quadrangles span a sizeable and representative part of this core. The 

oldest of the formations mapped in these quadrangles is the Swakane 

Biotite Gneiss, which was shown on the quadrangle maps as 

Cretaceous and older in age. The Swakane has yielded a middle 

Paleozoic metamorphic age, and also contains evidence of zircon inherited from some parent material more than 1,650 m.y. old. In this 

report, the Swakane is assigned an early Paleozoic or older age. It consists mostly of biotite gneiss, but interlayered with it are scattered 

layers and lenses of hornblende schist and gneiss, clinozoisite-epidote 

gneiss, and quartzite. Thickness of the Swakane is many thousands of 

meters, and the base is not exposed. The biotite gneiss is probably 

derived from a pile of siliceous volcanic rocks containing scattered 

sedimentary beds and basalt flows. Overlying the Swakane is a thick 

sequence of eugeosynclinal upper Paleozoic rocks metamorphosed to 

amphibolite grade. The sequence includes quartzite and thin layers of 

marble, hornblende schist and gneiss, graphitic schist, and smaller 

amounts of schist and gneiss of widely varying compositions. The 

layers have been tightly and complexly folded, and, in places, probably 

had been thrust over the overlying Swakane prior to metamorphism. 

Youngest of the supracrustal rocks in the area are shale, arkosic sandstone, and conglomerate of the Paleocene Swauk Formation. These 

rocks are preserved in the Chiwaukum graben, a major structural element of the region.

Of uncertain age, but possibly as old as any of the intrusive rocks in 

the area, are small masses of ultramafic rocks, now almost completely 

altered to serpentine. These occur either as included irregular masses 

in later intrusives or as tectonically emplaced lenses in metamorphic 

rocks. Also of uncertain age but probably much younger, perhaps as 

young as Eocene, are larger masses of hornblendite and hornblende 

periodotite that grade into hornblende gabbro. These are exposed on 

the surface and in the underground workings of the Holden mine.

Oldest of the granitoid intrusives are the narrow, nearly concordant 

Dumbell Mountain plutons, having a radiometric age of about 220 m.y. 

They consist of gneissic hornblende-quartz diorite and quartz diorite 

gneiss. Most contacts consist of lit-par-lit zones, but some are 

gradational or more rarely sharp. The plutons are typically catazonal. 

Closely resembling the Dumbell Mountain plutons in outcrop appearance, but differing considerably in composition, are the Bearcat 

Ridge plutons. These consist of gneissic quartz diorite and 

granodiorite. The Bearcat Ridge plutons are not in contact with older

dated plutons, but because their textural and structural characteristics 

so closely resemble those of the Dumbell Mountain plutons, they are 

considered to be the same age. Their composition, however, is suggestive of a much younger age. Cutting the Dumbell Mountain plutons 

is the Leroy Creek pluton, consisting of gneissic biotite-quartz diorite 

and trondjhemite. The gneissic foliation in the Leroy Creek is 

characterized by a strong and pervasive swirling. Cutting both the 

Dumbell Mountain and Leroy Creek plutons are the almost dikelike 

Seven-fingered Jack plutons. These range in composition from gabbro 

to quartz diorite; associated with them are contact complexes of highly 

varied rocks characterized by gabbro and coarse-grained hornblendite. 

Most of the rocks are gneissic, but some are massive and structureless. 

Radiometric ages by various methods range from 100 to 193 m.y.

Dikes, sills, small stocks, and irregular clots of leucocratic quartz 

diorite and granodiorite are abundant in the Swakane Biotite Gneiss 

and are locally abundant in the Seven-fingered Jack and other plutons. 

Although the leucocratic rocks vary little in appearance or composition, some, particularly those in the Swakane, were formed by 

metamorphic segregation, whereas the others are probably felsic differentiates of intrusive rocks.

The Tenpeak and White Mountain plutons are closely similar and 

are probably connected at depth. Rocks of the Tenpeak are more varied 

and range in composition from gabbro to granodiorite; quartz diorite is 

not only most common in the Tenpeak, but also constitutes, by far, the 

greatest bulk of the White Mountain pluton. Much of the rock in both 

plutons is somewhat gneissic, but some is nongneissic. The north end of 

the White Mountain pluton is bordered by a contact complex similar to 

those associated with the Seven-fingered Jack and other plutons in the 

area. Maximum potassium/argon ages determined on hornblende from 

the Tenpeak are about 90 m.y. Probably somewhat younger than the 

Tenpeak and White Mountain plutons is the Sulphur Mountain 

pluton. Only a small part of the pluton extends into the Holden 

quadrangle, and here the rocks are gneissic granodiorite.

The High Pass and Buck Creek plutons are tabular, somewhat silllike masses of granodioritic and quartz dioritic composition. Rocks in 

the Buck Creek pluton are entirely gneissic, whereas rocks only near 

the contacts or in the thinner parts of the High Pass are gneissic. In 

most places, the contacts of both plutons consist of lit-par-lit zones, 

but numerous dikes of the High Pass are present in the host rocks, especially the Sulphur Mountain pluton.

The Riddle Peaks pluton consists of layered and unlayered 

hornblende gabbro. Inasmuch as the pluton is cut on all sides by later 

intrusive rocks, its age relative to older plutons is not known, but it is 

almost certainly pre-Tertiary. Much of the gabbro is rhythmically 

layered, but some is unlayered or only vaguely layered. In places, thick 

sheets of unlayered gabbro alternate with equally thick sheets of 

rhythmically layered gabbro. The rock is mostly fresh and unaltered or
INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

recrystallized. No pseudosedimentary structures other than the 

gravity-stratified rhythmic layers were seen.

The Cardinal Peak pluton has a core consisting largely of 

granodiorite and quartz diorite and a rim of contact complexes containing large amounts of gabbro and coarse-grained hornblendite. The 

northern part of the intrusive is highly protoclastic throughout and 

contains numerous spindle- and canoe-shaped masses a third of a 

meter to several meters across and a few meters to several tens of 

meters long that are either partly or completely enveloped by rinds of 

fine-grained protoclastic material. These masses seem to have behaved 

as roller bearings during intrusion of the partly crystalline magma.

Tertiary intrusive rocks range in age from early Eocene to Miocene. 

Overall compositions do not vary much from pluton to pluton, but the 

composition can range from gabbro to quartz monzonite within individual plutons. Most of the plutons are typically epizonal, but parts 

of some are mesozonal. Oldest of the Tertiary plutons are the rather 

small epizonal to mesozonal Clark Mountain stocks consisting of 

quartz diorite and granodiorite. Next oldest is the tadpole-shaped late 

Eocene Duncan Hill pluton. This intrusive has been eroded to 

mesozonal depths at its thin tail and to only subvolcanic levels at its 

much wider head. The composition grades from quartz diorite in its 

mesozonal northern part to miarolytic quartz monzonite porphyry at 

its southern, subvolcanic part. Only about a million or so years younger 

than the 45-m.y.-old Duncan Hill is the Railroad Creek pluton. 

Numerous dikes satellitic to the pluton and small, irregular related 

masses are widely scattered in the northern part of the Lucerne 

quadrangle. Rocks in the pluton vary in both composition and texture, 

but granodiorite predominates and quartz diorite and quartz monzonite occur in small quantities. Similar in age to the Railroad Creek 

are the Copper Peak and Holden Lake plutons of hornblende-quartz 

gabbro. These plutons are notable for spectacular contact complexes 

consisting of rocks ranging in composition from quartz diorite to 

hornblendite that contain innumerable inclusions in various states of 

assimilation. The Larch Lakes and Rampart Mountain Plutons are undated, but closely resemble other late Eocene intrusives, and are 

believed to be of that age. The Larch Lakes pluton consists of rocks 

ranging in composition from quartz diorite to quartz monzonite, 

whereas the Rampart Mountain consists only of granodiorite and 

quartz monzonite. Both are sharply bordered, typically epizonal 

masses.

Preserved in the Chiwaukum graben is the Old Gib volcanic neck in 

which is preserved a Pelean spine. The neck has a radiometric age of 44 

m.y., consists largely of dacite porphyry, but contains some labradorite 

andesite and is cut by a few basaltic dikes. Other probably late Eocene 

rocks include a sizeable mass of intrusive breccia and dikes and irregular larger masses of generally fine-grained hornblende-biotitequartz diorite, biotite-quartz monzonite, and granodiorite.

Youngest of the major intrusives in the area is the Miocene Cloudy 

Pass batholith, now in the process of being deroofed. It is characterized 

by numerous subvolcanic features, intrusive breccias, and chilled contact complexes. Most of the rock is labradorite granodiorite, but quartz 

diorite and leucocratic quartz monzonite also occur. The batholith is 

bordered on the east by a layered complex of chilled rocks, the complex 

of Hart Lake.

From late Paleozioc time until the present, probably no sizeable 

time spans devoid of either magmatic or tectonic activity occurred in 

the northern Cascades. As a result, plutons vary greatly in depths to 

which they have been eroded. The older plutons, such as the Dumbell 

Mountain, have been carved to catazonal depths; the youngest, such as 

the Miocene Cloudy Pass, only now are being unroofed, and consequently show numerous subvolcanic features. The long, narrow 

Duncan Hill pluton is particularly illuminating, for it has been 

strongly tilted and, hence, differentially eroded. The strongly uplifted 

northern part has been eroded to mesozonal depths and is typically 

synkinematic, but the moderately uplifted south part has been eroded 

only to subvolcanic and epizonal depths and is decidedly

postkinematic. The terms "synkinematic" and "postkinematic" are 

probably meaningless when applied to these plutons as a whole, inasmuch as all are probably synkinematic at depth. Various other later 

Mesozoic and Tertiary plutons in the area more or less duplicate 

petrologic and structural features characteristic of given stretches 

along the length of the Duncan Hill.

All the major intrusives in the area reflect some degree of structural 

control, but such control is much more pronounced in the older 

plutons. The older plutons are decidely elongate and nearly concordant 

along strike but do crosscut host rocks downdip. Younger plutons are 

concordant only along parts of their contacts and tend to be much 

broader relative to their lengths, except for the conspicuously linear 

Duncan Hill mass. Furthermore, the younger intrusions tend to cut out 

large thicknesses of host rocks, at least to exposed levels. Because 

progressively younger plutons mostly are wide in proportion to their 

length, it seems likely that plutons in the area generally thin downward 

and become increasingly linear. The Dumbell Mountain plutons 

perhaps duplicate the appearance of the Cloudy Pass batholith at 

mesozonal depths.»Again, the Duncan Hill pluton illustrates well the 

methods whereby an intrusion adjusts to its room problem at different 

depths, that is, by wedging host rocks apart at lower levels and lifting 

and cutting them out at upper levels.

Ages of the plutons have been determined by a variety of radiometric 

methods. Potassium/argon methods work well for Tertiary intrusions, 

but only lead/uranium ages on zircon have provided reliable or 

believable ages for pre-Tertiary intrusives. Ages range from about 220 

m.y. for the Dumbell Mountain intrusions to about 22 m.y. for the 

Cloudy Pass batholith. The Cardinal Peak, Riddle Peaks, and Bearcat 

Ridge plutons have not been radiometrically dated but, on geologic 

evidence, are believed to be pre-Tertiary. At the time of intrusion of 

the Dumbell Mountain plutons, the upper Paleozoic sedimentary and 

volcanic rocks had already been metamorphosed to amphibolite grade. 

Although radiometric clocks have been reset by later plutonic events, 

the rocks have not been remetamorphosed, or only weakly so, since intrusion of Dumbell Mountain rocks.

Numerous samples of all the intrusive rocks have been modally 

analyzed, and one or more samples of all the major intrusions have 

been chemically analyzed. Compositions of the smaller intrusions are 

fairly uniform but, for most of the larger ones, variations are considerable. All the rocks are notably low in K2O relative to average intrusive rocks of similar silica content; furthermore, the older the rock, 

the greater the deficiency of K2O. Only the largest, mostly Tertiary, 

plutons are zoned. The Duncan Hill pluton progressively increases in 

SiOa and K?O and decreases in calcium, magnesium, and iron along its 

length from north to south and, consequently, from deep to shallow 

levels within it. A similar, although more erratic, trend also occurs 

between plutons of increasingly younger age and, hence, between more 

deeply and less deeply eroded masses. Variations in content of silica 

and especially of K2O in the Cloudy Pass batholith clearly seem to be 

the result of transfer of these constituents in supercritical aqueous 

solutions. The same processes probably also account for zoning in the 

Duncan Hill pluton and perhaps for compositional differences between 

more deeply and less deeply eroded plutons. Differentiation by crystal 

fractionation, although present, seems not to have been especially effective in presently exposed depths in the various plutons.

The textures of the older plutons have a crystalloblastic appearance, 

whereas the textures of younger plutons are typically igneous. It is unlikely, however, that the crystalloblastic-appearing textures are not the 

result of intense recrystallization in these rocks, but are the result of 

very slow cooling in catazonal regions of high temperatures and pressures. It seems extremely unlikely, for example, that recrystallization 

of the older plutons could have occurred and left unaffected the attitudes of gneissic foliation in disoriented inclusions. If these suppositions are true, then some of the metamorphic cycles and metamorphic 

suites detailed in the northern Cascades that have been based on the 

supposed metamorphism of various plutons are erroneous.
INTRODUCTION

INTRODUCTION

Exposed in the core of the northern Cascade Range is a 

suite of plutons that is perhaps unrivaled in the country 

for the diversity of geology and ages of plutons and 

depths to which plutons are exposed. Within the confines of single 15-minute quadrangles are plutons ranging in age from Triassic to Miocene and in depth zones 

from catazonal to subvolcanic marvelously revealed, 

furthermore, in a glacially scoured terrain of great relief. 

At one time most of these plutons were thought to be 

either part of or related to the so-called "Chelan 

batholith." Many of these plutons, however, are 

separated by time spans of tens of millions of years and 

by tectonic events so dramatic that an implied 

relationship indicated by the term "Chelan batholith" 

seems unwarranted.

This report presents the results of a study of these 

plutons carried out mostly during the geologic mapping 

of the Holden and Lucerne 15-minute quadrangles. 

These two quadrangles, together with the adjacent 

Glacier Peak quadrangle mapped by Crowder, Tabor, 

and Ford (1966), form a belt that crosses much of the 

plutonic core of the northern Cascades (fig. 1). This belt 

is representative of the core of the range, and statements 

and interpretations offered here probably apply with 

equal validity to the core as a whole. Inasmuch as some 

of the plutons in the Holden quadrangle extend into the 

Glacier Peak quadrangle, data concerning these plutons 

published by Crowder, Tabor, and Ford (1966) and 

Tabor and Crowder (1969) have been used freely. In addition, parts of some other plutons extending beyond the 

Holden and Lucerne quadrangles were investigated in 

reconnaissance. The Holden and Lucerne geologic 

quadrangle maps have been published previously (Cater 

and Crowder, 1967; Cater and Wright, 1967) and are not 

included in this report, although they should be considered an integral part of it and are referred to frequently. Figure 2 shows the location of various plutons 

described in this report. Field mapping was supplemented by examination of more than 900 thin sections of intrusive rocks and by 47 chemical analyses. 

Figure 3 shows the classification system for igneous rocks 

used in this report.

ACKNOWLEDGMENTS

I am indebted to the late Dwight F. Crowder and to C. 

A. Hopson, D. F. Kellum, R. W. Tabor, andT. L. Wright 

who helped map the Holden and (or) Lucerne 

quadrangles. To all of them I am also grateful for discussions that helped formulate some of the conclusions 

presented here. Crowder also examined many thin sections. I am particularly grateful to Hopson for unpublished data and mapping he contributed concerning 

the Duncan Hill pluton south of the Lucerne quadrangle.

PREVIOUS WORK

Prior to the mapping of the Holden and Lucerne 

quadrangles by the U.S. Geological Survey, work in the 

quadrangles was limited to descriptions of the rocks at 

Red Mountain by Richarz (1933), a discussion of geologic 

features at the Holden mine by Youngberg and Wilson 

(1952), and reports on two small areas mapped by 

Dubois (1954, 1956) and Morrison (1954).

TECTONIC SETTING

The northern Cascades were carved from an exotic 

block or mini continent of continental crust that accreted 

to the North American continent during Mesozoic time 

(fig. 4). Many authors, including Da vis, 1977; Davis, 

Monger, and Burchfiel, 1978; Dickinson, 1976; 

Hamilton, 1969, 1978; and Vance, 1978, have applied the 

concepts of plate tectonics to the region. They are not 

unanimous, however, on the origin of the minicontinent. 

Hamilton (1978, p. 42) considered it a far-travelled block 

that collided with the continental margin in middle 

Cretaceous time, whereas Davis, Monger, and Burchfiel 

(1978, p. 15) considered it a fragment of the Okanogan 

continental-margin terrain torn from the North 

American continent along a dextral transcurrent fault 

trending at a low angle to the continental margin. They 

called this fragment "Cascadia," and stated (p. 16), 

"Minimum right-slip of 160 km (100 miles) is represented by the length of unbroken Cascade crystalline terrain west of Jura-Cretaceous in the Methow trough. The 

distance is measured from the southern end of the 

trough, near Methow, where Cascade and Okanogan 

crystalline rocks are in fault contact, to the Hope area of 

British Columbia where Cascade core rocks are faulted

125

NORTHERN 

ROfcKY

TS

Grand

eian

'Chela!/ 

Entiat 

Wenatchee 

v COLUMBIA

FIGURE 1. Index map of Washington showing physiographic 

provinces and locations of Holden and Lucerne quadrangles.
INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

121°00' 120°30'

FIGURE 2. Map showing locations of the plutons in the Holden and Lucerne quadrangles. Patterned areas are metamorphic rocks.

1. Dumbell Mountain plutons

2. Bearcat Ridge plutons

3. Leroy Creek pluton

4. Seven-fingered Jack plutons

5. Entiat pluton

6. Tenpeak pluton

7. White Mountain pluton

8. Sulphur Mountain pluton

9. High Pass pluton

10. Buck Creek pluton

11. Riddle Peaks pluton

12. Cardinal Peak pluton

13. Clark Mountain stocks

14. Duncan Hill pluton

15. Larch Lakes pluton

16. Rampart Mountain pluton

17. Old Gib volcanic neck

18. Intrusive breccia

19. Hornblende-biotite-quartz diorite

20. Railroad Creek pluton

21. Copper Peak pluton

22. Holden Lake pluton

23. Biotite-quartz monzonite and granodiorite

24. Cloudy Pass batholith

25. Leucocratic quartz monzonite

out against the Hope-Straight Creek fault system. The 

northernmost extent of Cascade rocks west of the 

Straight Creek fault is not known because of the 

obliterative effects of the Coast Range Batholithic complex." They further postulated that the Ross Lake fault 

or a precursor of it was the most likely place where this 

shift occurred. The pull apart from the North American 

continent is assumed to lie beneath the Miocene basalts 

of the Columbia River plateau.

In any event the minicontinent is separated from the 

pre-Carboniferous continental shelf in northeastern 

Washington by some hundreds of kilometers, a gap now

consisting of large masses of island-arc and oceanic assemblages intruded by very large amounts of granitic 

material.

PREINTRUSIVE ROCKS

The oldest plutons in the area intruded a terrain of 

metamorphic rocks of late Precambrian and late 

Paleozoic age. Younger plutons, of course, intruded not 

only the metamorphic rocks but also the older plutons. 

The oldest of the formations exposed in the area, and 

probably in the northern Cascades, is the Swakane
PREINTRUSIVE ROCKS

0 5 

Plagioclase

35 65 100 

Potassium feldspar

FIGURE 3. Triangular diagram showing the modal rock classification 

system used in this report.

121TJO' BRITISH COLUMBIA

WASHINGTON OKANOGAN

ARC COMPLEX

Triassic and Jurassic

accretionary terrain

Mesozoic 

ocean floor

Pa I eozo ic- J u ra ss ic 

island arc and

oceanic 

assemblages 

MtTHOW GRABEN

IlurassicCrefaceous

strata

NORTHERN CASCADES 

5 Precambrian-Tertiary 

S plutonic complex 

Cascadia

CHIWAUKUM X 

GRABEN

Columbia Plateau 

Miocene basalt

FIGURE 4. Tectonic sketch map of north-central Washington showing 

the relation of the Holden and Lucerne quadrangles to the regional 

tectonic framework. Named faults separating major structural elements restored. Heavy lines are faults; lighter lines are contacts.

Biotite Gneiss. The Swakane is possibly equivalent to at 

least part of the Custer Gneiss of McTaggart and 

Thompson (1967), which was originally called the Custer 

Granite Gneiss by Daly (1912, p. 525-526). The formation has also been called the Skagit Gneiss by Misch 

(1952, p. 12-14) and others, but the name "Skagit" was 

preempted by Daly in 1912 for a sequence of volcanic 

rocks along the Canadian border west of Ross Lake. 

Overlying the Swakane is a sequence of metamorphosed 

eugeosynclinal, rather thinly laminated, complexly 

folded rocks of late Paleozoic age that is widely exposed 

in both quadrangles and elsewhere in the region. The unmetamorphosed Paleocene Swauk Formation outcrops 

in a few locations in the Chiwaukum graben (Willis, 

1953) within the Holden quadrangle.

SWAKANE BIOTITE GNEISS

The Swakane Biotite Gneiss is predominantly a lightbrown to brownish-gray, fine- to medium-grained, 

strongly foliated rock. Intercalated with the gneiss, 

locally, are rather thin layers of hornblende schist and 

gneiss, gneisses predominantly of clinozoisite-epidote, 

and more rarely, thin layers of quartzitic rock. Some of 

these layers can be traced for kilometers and represent 

an original compositional layering or bedding. Kyanite 

occurs sparsely on Phelps Ridge but is rare elsewhere, 

and garnet is common in many places. Streaks of biotite 

on the plane of foliation commonly define a marked 

lineation. Lenses and pods of quartz and irregular 

masses of leucocratic quartz diorite are notably abundant in some places and common elsewhere. Other than 

compositional layering, no original textural or structural 

features remain. Probably many thousands of meters of 

the formation are exposed in the northeast part of the 

Lucerne quadrangle, and equally great thicknesses are 

exposed elsewhere in the region; the base of the Swakane 

is not known to be exposed. The Swakane was assigned a 

Cretaceous and older age on the Lucerne and Holden 

quadrangle maps (Cater and Crowder, 1967; Cater and 

Wright, 1967). Mattinson (1972) obtained ages of more 

than 1,650 m.y. (age of parent material) from zircons in 

the rock along the Columbia River, but he also got 

Paleozoic ages of about 415 m.y. (metamorphic age) 

from zircons in the biotite gneiss along the Skagit River 

about 65 km northwest of the Lucerne quadrangle. On 

the basis of a minimum age of 415 m.y., the Swakane is 

considered early Paleozoic or older in this report. Staatz 

and others (1972, p. 3774, table 2) mapped these rocks as 

Custer Gneiss of McTaggart and Thompson (1967), and 

Misch (1952, 1966) mapped them as Skagit Gneiss. The 

Swakane on the Columbia River is directly traceable to 

the Swakane in the Holden quadrangle, which in turn is 

identical to rock mapped as Swakane in the Lucerne
INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

quadrangle. Misch (1966, p. 107, fig. 7-1) showed the 

Skagit Gneiss on the Skagit River as continuous with the 

Swakane of the Lucerne quadrangle. Possibly 

metamorphism of the rocks in the area between the two 

localities has obscured the relation of the Custer to the 

Swakane.

The nature of the material from which the Swakane 

Biotite Gneiss is derived is not known with certainty. 

Hornblende-rich layers may have been basaltic flows, 

and quartzitic and epidote-rich layers probably were 

sedimentary beds. Waters (1932, p. 616) considered it 

likely that the biotite gneiss was derived from mostly 

arkosic material, a possibility that still remains; but 

more recently Hopson (in Mattinson, 1972, p. 3773) considered a volcanic derivation more likely. The accumulation of a nearly uniform pile of arkose many thousands of 

meters thick of the wide areal extent of the Swakane and 

its equivalents seems unlikely. Arkosic piles such as the 

Permian Cutler Formation in southwest Colorado and 

Utah tend to be segregated by sedimentary differentiation into interlayered beds of sandstone, mudstone, and 

shale farther from source areas (Cater, 1970). The 

Swakane and its equivalents are remarkably uniform in 

composition throughout their outcrop area and show no 

tendency toward original segregation into contrasting 

beds. The chemical composition of the biotite gneiss approximates that of dacite; table 1 shows an analysis of a 

composite sample of representative specimens of biotite 

gneiss.

With the foregoing in mind, it seems more likely that 

the Swakane Biotite Gneiss was probably derived from a 

huge, fairly silicic volcanic pile. Scattered basaltic flows 

now form the hornblende gneiss and schist layers, and

TABLE 1. Chemical and spectrographic analyses of Swakane Biotite 

Gneiss, central Washington

[Na2O and K2O determined by flame photometer by Violet Merritt. Fe2O3 , MgO, and CaO 

determined by atomic absorption by Violet Merritt. FeO determined volumetrically by H. 

H. Lipp. SiO2 and Al2Oi determined colorimetrically by G. D. Shipley and G. T. Burrow. 

Spectrographic analysis by Harriet Neiman.]

Chemical analys

SiO2 ------------

Fe2O3 -----------

FeO - ----- -----

MgO -------------

CaO -------------

NaaO------ ----

K

c\

is (percent)

/?Q 0

ic n

....--- 3.45

9 8

1 Kf)

-..- 2 04

o ni

1 QR

QO Hfi

Ti

Mn

Co

Cu

Ga

Ni

Pb

c,.

V -

v

VVi

Zr

Spectrographic analysis (percent)

U.o

-------------------- .07

nc

nnm

..................... .0015

nno

..................... .0015

OO07

no

01^

..................... .0015

02

the quartzite and mica schist layers were probably thin 

sedimentary beds deposited in small, ephemeral basins 

in the volcanic terrain.

The Swakane Biotite Gneiss has been warped into 

steep-sided but generally open folds having steep to vertical axial planes. Waters (1932, p. 621) noted that the 

same type of folds characterize the Swakane farther to 

the south along the Columbia River. Generally, attitudes 

of the gneiss are uniform through considerable 

thicknesses, but locally attitudes of foliation are 

irregular, particularly where disturbed by various 

intrusives.

LATE PALEOZOIC METAMORPHIC ROCKS

Overlying the Swakane Biotite Gneiss is a highly 

diverse sequence of metamorphosed eugeosynclinal 

rocks consisting largely of rather thinly layered, highly 

and complexly folded hornblende and biotite-hornblende schist and gneiss, biotite schist, clinopyroxenebiotite schist, graphitic schist, quartzite, and lenses of 

marble (fig. 5). These rocks crop out on opposite sides of 

the Chiwaukum graben, which is mostly underlain by 

the Swakane. The rocks to the east of the graben were 

called "younger gneissic rocks of the Holden area" on 

the Holden and Lucerne geologic quadrangle maps, and 

the rock to the west, the "rocks of the Napeequa River 

area." The rocks in the two belts are almost surely parts 

of a single series or group, but attempts at stratigraphic 

correlations between the belts have been thwarted, in 

part, probably, by rapid facies changes combined with

FIGURE 5. Interlayered upper Paleozoic quartzite, biotite schist, and 

hornblende gneiss, upper Klone Creek, Lucerne quadrangle.
PRE-TERTIARY INTRUSIVE ROCKS

depositional wedging, but more critically by 

metamorphic changes, extreme structural complexities, 

and mangling by the various intrusions. Sedimentary 

features are preserved well enough to determine tops of 

beds in a few places on the ridge north of Holden, 

although the rocks are metamorphosed to amphibolite 

grade. Search elsewhere, however, failed to find similar 

unequivocal evidence for tops, despite the littlemodified aspect of the beds in some places. Isoclinal 

folding and other structural complexities render 

thickness determinations highly uncertain, but in the 

Holden quadrangle the exposed thickness cannot be less 

than about 1.5 km, and it may well be at least twice that 

much. If the "rocks of the central schist belt" of the 

Glacier Peak quadrangle (Crowder and others, 1966) are 

also part of the same sequence, as seems likely, then the 

thickness could be very much greater. Zircons from a 

layer of metamorphosed keratophyre tuff in the Holden 

quadrangle were dated by Mattinson (1972, p. 3773) as 

265±15 m.y. old; hence, the rocks are of late Paleozoic 

age.

The structure of the upper Paleozoic metamorphic 

rocks differs radically from that of the underlying 

Swakane Biotite Gneiss and is far more complex. The 

major folds in the Swakane are broad, open, and mostly 

fairly simple, whereas those in the upper Paleozoic rocks 

are tightly compressed and overturned or actually inverted. For example, sedimentary structures indicate 

that the antiform in these rocks that trends across the 

Lucerne quadrangle is an inverted syncline. East of the 

Chiwaukum graben, these rocks seem to have been 

thrust westward over the probably already metamorphosed Swakane before they became metamorphosed. 

West of the graben, great thicknesses of beds are missing 

from the northeast side of the synform of upper Paleozoic 

metamorphic rocks, where these upper Paleozoic rocks 

rest on the Swakane, or where the rocks are separated 

from the Swakane, by a sheet of intrusive rocks. As is 

detailed in the text that follows, the structure of both sequences of metamorphic rocks has had a profound influence on the form of the various plutons.

The metamorphic rocks are overlain by shale, arkosic 

sandstone, and conglomerate that were mapped as the 

Paleocene Swauk Formation. Later work (Whetten, 

1976) indicated that the rocks are of late Eocene age; 

Whetten obtained a fission-track age of 44.1 ±4.3 m.y. on 

zircons from a tuff near the base of the sequence. In the 

study area, the sedimentary rocks have been preserved 

only in the Chiwaukum graben in the Holden quadrangle, but they underlie large areas elsewhere in the 

northern Cascades. Within the Holden quadrangle, only 

a few dikes cut the formation, although farther south are 

a few small plugs and extensive dike swarms. Of particular interest are numerous cobbles in the conglomerates consisting of volcanic rocks. These volcanic

rocks may be the extrusive equivalents of some of the 

late Cretaceous intrusive rocks described here.

PRE-TERTIARY INTRUSIVE ROCKS

ULTRAMAFIC ROCKS

A number of small masses of ultramafic rocks ranging 

from only a few meters to a few hundred meters across 

crop out in the area. The smaller ones consist of serpentine, and some of the serpentine has been extensively 

altered to talc or tremolite. The larger ones, on the other 

hand, are highly variable in composition and consist of 

gabbro, hornblendite, and peridotite. The serpentine 

masses mostly occur in a northwesterly trending zone extending through the southwest part of the Holden 

quadrangle to the northwestern part of the Glacier Peak 

quadrangle. The ultramafic masses of variable composition are confined to the Holden mine-Buckskin Mountain area and are probably considerably younger and unrelated to the serpentine bodies.

Serpentine occurs as scattered lenses apparently tectonically emplaced in gneiss and schist or in the inter layered zone in the Tenpeak pluton. Rare masses only 

a few meters across have been seen as inclusions in 

various quartz diorite plutons scattered about the study 

area. The largest masses are near the divide at the head 

of Boulder Creek in the Holden quadrangle. Contacts, 

where seen, are sharp and either sheared or unsheared. 

The serpentine is light green to black and either 

schistose and sheared or dense and structureless. Where 

altered to talc or tremolite, the rock is light green or 

nearly white; such masses are mostly confined to quartz 

diorite.

Thin-section examination revealed that the serpentine 

contains rare relics of olivine in a felted mat of antigorite; abundant magnetite occurs mostly as sagenitic 

webs of irregular grains. Most thin sections also contain 

talc and tremolite, and some consist almost entirely of 

talc. Scattered picotite grains are accessory.

Ultramafic rocks in the Holden mine and on Buckskin 

Mountain differ considerably from the serpentine bodies 

and from other ultramafic masses that have been 

described in the northern Cascades (for example, Ragan, 

1963, and Southwick, 1974). Most ultramafic masses in 

the northern Cascades are of Alpine type and consist of 

little but saxonite or dunite or their serpentinized 

products, whereas the ultramafic rocks in the Holden 

area consist largely of hornblendite and hornblende 

peridotite that grade into hornblende gabbro. Saxonite 

and dunite are absent. Some of the peridotite in the 

Holden mine contains numerous coarse-grained gabbroic 

orbicules as much as 7 cm across (fig. 6). The rocks are 

dark green to black, coarse to very coarse grained, and 

some crystals are more than 2 cm across. The largest of
INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

FIGURE 6. Gabbroic orbicules in peridotite from the Holden mine, 

Holden quadrangle.

the masses cropping out on Buckskin Mountain is about 

300 m across; the size of those in the Holden mine are not 

known, but some exceed several hundred meters. Contacts with older rocks are either sharp and intrusive or 

faulted. Contact effects on intruded rocks are minimal. 

Microscopic examination of the ultramafic rocks confirms the heterogeneity evident in hand specimen. 

Hornblende is the only major constituent common to all 

the rocks, and it is optically similar in all facies of the 

rock regardless of other constituents. Hornblende 

crystals are commonly anhedral and pleochroic from 

nearly colorless to light brown. The intensity of 

pleochroism varies considerably within a single crystal, 

some parts of most crystals being nearly colorless in all 

orientations; in others, the brown shades into light 

green. Some grains are loaded with Schiller-like inclusions that may be spinel. In many of the rocks, 

hornblende has been either replaced or at least partly 

rimmed by tremolite containing magnetite dust. Pyroxene occurs only in peridotites, and in these it may be 

either clinopyroxene alone or both clino- and orthopyroxene. Most crystals are either euhedral or subhedral, but 

some rounded grains occur as poikilitic inclusions in 

hornblende. Small amounts of olivine are scattered 

through some of the hornblendite, and as much as 30 

percent is in hornblende peridotite. Olivine is generally 

much altered to antigorite and magnetite. Light-colored 

biotite or phlogopite is common in most of the rocks and 

makes up 20 percent of some of them. It is pleochroic 

from colorless to light brown and is mostly shredlike. 

Plagioclase in amounts approaching 50 percent distinguishes the gabbros from the other rock types, 

although very small amounts of interstitial bytownite 

are found in some peridotite. Most of the plagioclase is 

bytownite, having an average composition of about Ango, 

but in some of the more felsic gabbro the plagioclase is 

sodic labradorite. Plagioclase in orbicular gabbro is 

bytownite, however. Regardless of composition, plagioclase is subhedral to euhedral and shows both oscillatory and patchy zoning. Magnetite, apatite, and ilmenite, which is commonly rimmed by sphene, are fairly 

abundant accessories. Mafic constituents in most of the 

rocks are variously altered to antigorite (replacing 

olivine and pyroxene), tremolite (replacing hornblende), 

and chlorite (replacing hornblende and phlogopite). In 

the Holden mine, various sulfides, including pentlandite, exsolved from pyrrhotite, locally replace both gabbro and ultramafic rocks.

Ages of the ultramafic rocks are not known with precision; the serpentine masses in the Holden and Glacier 

Peak quadrangles are, of course, older than the intrusive 

rocks in which they occur and may well be the oldest igneous rocks in the area. The hornblendic rocks in the 

Holden area are probably much younger and may be as 

young as late Eocene, inasmuch as they may be a facies 

of the mafic contact complex that envelops the north end 

of the Duncan Hill pluton.

DUMBELL MOUNTAIN PLUTONS

Rocks of the Dumbell Mountain plutons were 

described in detail by Crowder (1959). Since publication 

of Crowder's report, however, these rocks have been reexamined both in the light of what was learned from the intensive study of other intrusions in the area and from 

radiometric dating not then available. As a result, some 

of Crowder's earlier interpretations and conclusions 

seem untenable. He concluded that the Dumbell Mountain plutons, in addition to others now known to be 

much younger, were merely facies of a large granitized 

mass that has been locally mobilized. The present study 

indicates that these conclusions were probably invalid.

As Crowder (1959) showed, the Dumbell Mountain 

rocks within the mapped area consist of three separate 

but closely related units that I consider to be three distinct plutons. From the north border of the Holden 

quadrangle they extend south-southeastward into the 

Lucerne quadrangle where they either pinch out or are 

cut off by the late Eocene Duncan Hill pluton. They 

possibly correlate with Misch's (1966, fig. 7-1) 

"Marblemount Meta Quartz Diorite" to the northwest, 

which Mattinson (1972) showed to be of the same age. 

Misch (1966) considered the Marblemount a part of a 

pre-Middle Devonian "basement" consisting of 

regionally metamorphosed orthogneisses which he 

showed, citing theses maps of Tabor (1958) and Grant 

(1966), in thrust relation with the "Cascade River 

Schist," presumably equivalent to "younger gneissic 

rocks of the Holden area" of the Holden and Lucerne 

geologic quadrangle maps. Inasmuch as Misch's map 

(1966, fig. 7-1) is of an area extending well into the 

Holden quadrangle, he shows thereby quartz diorite of
PRE-TERTIARY INTRUSIVE ROCKS

Dumbell Mountain thrust over "younger gneisses of the 

Holden area." The Dumbell Mountain plutons are in 

fact neither older than nor thrust over the "Cascade 

River Schist" in the Holden quadrangle; rather, they are 

unrecrystallized or only incipiently recrystallized igneous rocks about 220 m.y. old (Mattinson, 1972) that 

are intrusive into, instead of thrust over, the metasediments in the Holden area. The evidence supporting these 

conclusions is presented, where appropriate, in the pages 

that follow. In any event, despite the resemblance of the 

"Cascade River Schist" to the "younger gneissic rocks of 

the Holden area," either the correlation is wrong or the 

"Marblemount Meta Quartz Diorite" is older than the 

Dumbell Mountain plutons.

Inasmuch as Crowder (1959) described the distribution, petrography, and contact relations of the Dumbell 

Mountain plutons in considerable detail, they are only 

summarized here.

The Dumbell Mountain plutons are narrow, nearly 

concordant masses of quartz diorite that trend northnorthwest, more or less parallel to the attitudes of the 

metamorphic host rocks. Sheets or screens of schists and 

gneisses, some of them of mappable size, are common in 

the plutons. These are particularly abundant in the 

hornblende-quartz diorite augen gneiss between 

Railroad and Ice Creeks. In addition to these, a thin 

screen of hornblende gneiss and schist about 8 km long 

separates the quartz diorite augen gneiss from gneissic 

hornblende-quartz diorite between Big Creek and Ice 

Creek, and a similar screen of about the same size 

separates gneissic quartz diorite from the Leroy Creek 

pluton.

Contacts between the plutons and the metamorphic 

rocks are varied: sharp in some places, gradational in 

others, but more commonly characterized by lit-par-lit 

inter layering of quartz diorite and metamorphic rocks. 

Alternating layers in the lit-par-lit zones are several centimeters to tens of meters thick, and, indeed, some are 

almost the size of the mapped screens. Some layers of 

schist and gneiss have been wedged frorr the walls by 

quartz diorite and are inclined to the foliation of the 

quartz diorite. In general, contacts between layers are 

sharp, but layers of metamorphic rocks tend to fray out 

along strike and grade into and contaminate the intrusive material. Some hornblende schist and gneiss 

layers and inclusions have dark, more hornblende-rich 

margins from which felsic material has migrated (fig. 7); 

in fact, many thinner layers and inclusions consist 

almost entirely of hornblende.

Quartz diorite near contacts characterized by lit-parlit injections tend to be crowded with inclusions of host 

rocks. As would be expected where host rocks are 

strongly foliated, inclusions of host rocks in the intrusive 

rock near contacts are mostly platy or discoidal, but 

many are more or less equidimensional and angular. As a

FIGURE 7. Dumbell Mountain hornblende-quartz diorite augen 

gneiss containing inclusions with mafic margins, Holden 

quadrangle.

rule, longer dimensions of inclusions dimensions that 

usually accord with the planes of foliation in the inclusions are parallel to the foliation of the quartz 

diorite, but some are inclined at high angles. Had foliation of the quartz diorite resulted from postintrusion 

recrystallization, as Crowder (1959) earlier thought and 

as Misch (1966) assumed by correlating these rocks with 

his ancient basement rocks, it seems unlikely that the 

angular relation between foliation of the quartz diorite 

and foliation of inclusions defined by elongate and platy 

minerals could have been preserved. Furthermore, the 

intricately swirled foliation, particularly characteristic 

of the hornblende-quartz diorite augen gneiss but occurring in the other Dumbell Mountain plutons, is not the 

type likely to result from regional metamorphism; the 

host rock schists and gneisses are devoid of this type of 

foliation. Swirled foliation, in fact, occurs locally in most 

of the plutons regardless of age and results from flowage 

during intrusion.

Locally contacts of plutons with metamorphic rocks 

are gradational, in most places through zones only a few 

tens of meters or less thick. In some places, however, as 

on the ridge south of the glacier on the east side of Copper Peak, the gradational contact zone is a few hundred 

meters thick. As contacts of plutons are approached, the 

grain size and proportion of felsic material in the 

hornblende schist and gneiss, of which the host rocks 

largely consist, increases, and thin seams of igneous 

material have been insinuated along foliation planes. 

Closer to the plutons, the amount of igneous material increases, and the metamorphic material becomes more 

thoroughly incorporated in the rock mass. Dikes and sills
10 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

of quartz diorite cut these gradational contacts just as 

they do contacts marked by lit-par-lit zones where there 

is a marked difference between igneous and metamorphic material. Gradations are equally evident in thin 

sections, as is discussed later.

Although each of the Dumbell Mountain plutons is 

closely similar to the others in chemical and mineralogic 

composition, they differ significantly in outcrop appearance. These differences are mostly a function of 

gneissic foliation; its nature, its degree of segregation 

into light and dark laminae, and its persistence of attitude or prevalence of swirling. For each of the plutons 

there is a unity of gneissic characteristics that is more or 

less distinctive, although there is considerable overlap of 

these in the different plutons. Thus scattered masses of 

augen gneiss occur in both the gneissic hornblendequartz diorite and the hornblende-quartz diorite gneiss 

plutons, but augen texture is the characteristic feature of 

the hornblende-quartz diorite augen gneiss pluton. 

Despite the similarities among the different plutons, 

contact relations point to a sequence of emplacement. 

Oldest is the hornblende-quartz diorite gneiss; this rock 

was intruded locally by gneissic hornblende-quartz 

diorite, but more commonly the contacts between the 

two appear to be completely gradational and nothing 

suggestive of an age difference is apparent. Hornblendequartz diorite augen gneiss, on the other hand, clearly 

intrudes quartz diorite gneiss almost throughout their 

contact lengths, yet in the one area where the augen 

gneiss is in contact with gneissic quartz diorite, on the 

north side of Railroad Creek upstream from Holden 

Creek, the relations are equivocal.

The rocks in the Dumbell Mountain plutons differ little mineralogically; the principal difference is in the 

composition of the plagioclase, which ranges from about 

Anss to about Arise in the hornblende-quartz diorite 

gneiss and augen gneiss and from about Anso to An5o in 

the gneissic hornblende-quartz diorite. Most abundant 

in all the plutons are rocks containing plagioclase having 

a composition of about Ans8 ; considerable but lesser 

amounts of rocks in all the plutons contain calcic 

andesine of about An4 ?, and in the gneissic quartz diorite 

pluton, about one-fourth of the thin sections examined 

contained andesine of about Ans2. Rocks containing 

andesine of compositions intermediate between these 

peaks are rare. Megascopic appearance or texture give no 

clue to the composition of the plagioclase of any given 

rock, although biotite tends to occur more commonly in 

rocks containing less calcic andesine.

Since the Dumbell Mountain, Leroy Creek, Entiat, 

and Seven-fingered Jack plutons were described by 

Crowder (1959), the Dumbell Mountain pluton and rock 

of the Chelan Complex Entiat and Seven-fingered Jack 

plutons have been radiometrically dated by Mattinson 

(1972), and these rocks have been more thoroughly examined petrographically. The textures seen in many of 

the dated rocks where there is no question of recrystallization, particularly some of the older and deeper seated 

rocks, has made apparent the need for a reappraisal of 

what Crowder called "crystalloblastic" textures in the 

Dumbell Mountain and, for that matter, of the texture 

in the younger Seven-fingered Jack, Entiat, and Leroy 

Creek plutons. In my opinion, none of the rocks in any of 

these plutons are crystalloblastic; many, however, did 

crystallize under stress and most of the gneissic rocks 

show varying degrees of protoclasis.

Plagioclase is the mineral most notably affected by 

protoclasis because it was the first to crystallize and 

seems to have been the only crystalline component in the 

magma when protoclasis began or at least these were 

the only grains of sufficient size to have effectively impinged on each other during the grinding process that accompanied intrusion. Locally, however, larger crystals of 

hornblende have been broken and distorted protoclastically and, in some places, protoclasis passed into 

cataclasis where stresses continued after the plutons had 

completely crystallized. Plagioclase grains in the 

protoclastic rock are rounded and abraded; many grains 

consist of a number of slightly rotated fragments (fig. 8). 

Fractures separating the fragments end at grain boundaries, and later hornblende, quartz, or biotite grains 

commonly have formed or replaced plagioclase along 

these fractures (fig. 8), but the later grains themselves 

are undeformed. Nearly every thin section of Dumbell 

Mountain rocks contains a few plagioclase grains where 

a few faint oscillatory and patchy zonings may be seen 

(fig. 9). Oscillatory zones in many grains are truncated, 

which indicates that such grains are but fragments 

broken from larger crystals during protoclasis. In some

FIGURE 8. Gneissic hornblende-quartz diorite from the Dumbell 

Mountain plutons, Holden quadrangle. Note fine-grained aggregates 

of quartz and sodic oligoclase filling fractures in andesine.
PRE-TERTIARY INTRUSIVE ROCKS 11

FIGURE 9. Oscillatory- and patchy-zoned andesine in hornblendequartz diorite gneiss from the Dumbell Mountain plutons, Holden 

quadrangle. See figure 14 for hand sample.

crystals, oscillatory and patchy zoning are preserved 

only in untwinned or only weakly twinned parts of 

crystals, suggesting thereby that the general lack of both 

types of zoning merely reflects destruction of them by 

twinning. A great many individual plagioclase crystals 

are twinned according to multiple laws, a feature many 

authors have detailed as suggestive of igneous origin 

(Gorai, 1951; Smith, 1958; Vance, 1961, 1962; Turner, 

1951). The occurrence of patchy zoning in most thin sections of Dumbell Mountain rocks virtually precludes 

recrystallization following emplacement of the plutons 

and is strong presumptive evidence of magma transport 

from greater depths (Vance, 1965). Some sieve-textured 

hornblende crystals are clearly derived from partly assimilated metamorphic rocks, but some result from incomplete replacement of plagioclase by hornblende; 

such grains not uncommonly contain groups of 

simultaneously extinguishing inclusions apparently 

derived from a preexisting single crystal of plagioclase.

Partly for the sake of convenience and partly because 

significant differences do exist between them, the 

plutons are described separately. It should be emphasized, however, that although each pluton is a separate 

entity, they are closely related and are probably derived 

from a common magma in which differentiation had little effect at least at the presently exposed level, which 

the evidence indicates is catazonal.

The location of modally analyzed specimens of the 

Dumbell Mountain plutons are shown on figure 10, the 

modal analyses are presented in table 2, and the

chemical and spectrographic analyses are presented in 

table 3. The modes are also plotted on a quartz - 

potassium feldspar-plagioclase triangular diagram (fig. 

11) and the norms are shown on figure 12. Compositions 

are plotted on a variation diagram (fig. 13).

HORNBLENDE-QUARTZ DIORITE GNEISS

Hornblende-quartz diorite gneiss crops out from the 

north edge of the Holden quadrangle on Bonanza Peak to 

Mount Fernow where it pinches out, a distance in the 

mapped area of 11 km. It lies between the younger 

quartz augen gneiss of Dumbell Mountain on the east 

and probably still younger gneissic quartz diorite to the 

west. As already noted, its contacts with these younger 

rocks range from sharp and intrusive to gradational.

The megascopic appearance of this rock is more uniform than that of the other Dumbell Mountain rocks, 

although the amounts of schlieren and incorporated 

material vary considerably from place to place. Nearly 

all of it is strongly and rather uniformly gneissic (fig. 14). 

The hornblende forms flat clusters or long black strings 

of needles that give much of the rock a well-defined 

lineation that plunges southeastward at low to moderate 

angles. Unlike the other Dumbell Mountain rocks, this 

gneiss is virtually but not entirely unswirled, and the 

foliation maintains rather constant attitudes through 

considerable distances.

Thin-section examination of the hornblende-quartz 

diorite gneiss showed it to consist largely of plagioclase, 

hornblende, and quartz, and in about half the sections a 

little biotite is present. Small quantities of magnetite, 

titanite, and apatite are accessory. In a few thin sections, 

very small amounts of potassium feldspar occur interstitially, or more commonly, as tiny veinlets. Chlorite, 

clinozoisite-epidote, and sericite, mostly in small quantities, are secondary. Plagioclase is mostly fresh and 

ranges in composition from andesine having an average 

composition of about An38 to sodic labradorite having an 

average composition of slightly more than An50 . Individual crystals range from subhedral to anhedral, and 

many are rounded and obviously abraded; a few grains 

in most sections show four or five oscillatory zones and 

equally faint patchy zoning. In a few sections showing 

hypidiomorphic textures, many crystals have welldefined oscillatory and patchy zoning, but the zones in 

any given crystal do not exceed four or five (fig. 9). 

Hornblende occurs as euhedral to anhedral grains; much 

of it forms aggregates resembling poikilitic hornblende, 

but such groups do not form single crystals, although 

this is commonly not apparent except under crossed 

nicols. The pleochroic formula for hornblende is X, straw 

yellow to light greenish yellow; Y, green; and Z, dark 

green or dark bluish green. The pleochroic formula for 

biotite is X, light yellow and Z, moderate to dark brown.
12

48°15'

INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

120°45'

48°0

EXPLANATION 

Gneissic hornblende-quartz diorite

Hornblende-quartz diorite 

augen gneiss

Hornblende-quartz diorite gneiss

Sample locality

FIGURE 10. Map showing location of modally analyzed samples from the Dumbell Mountain plutons, central Washington. Sample

analyses are given in table 2.
PRE-TERTIARY INTRUSIVE ROCKS 13

TABLE 2. Modal analyses of samples of hornblende-quartz diorite and hornblende-quartz diorite gneiss from the Dumbell Mountain plutons

[Values are in percent. Leaders (- - -), not present]

Sample

No.

Potassium

Plagioclase feldspar Quartz Biotite

Accessory 

and secondHornblende ary minerals

Total 

mafic

i minerals

Anorthite in 

plagioclase crystals (percent)

Average Core Rim Remarks

Gneissic hornblende-quartz diorite

1

4

5

9

13

14

15

17

18

19

21

22

23

24

29

30

31

36

38

41

45

48

49

50

51

52

53

54

55

56

57

55.0

41.4

49.9

43.7

55.6

61.7

52.8

60.2

50.9

41.6

59.0

49.2

62.5

43.5

57.0

45.0

52.6

47.8

58.8

56.9

47.7

53.6

40.0

48.5

47.9

48.6

49.0

47.3

47.4

50.6

46.4

13.2

4.5

17.6

6.4

5.4

14.1

7.4

21.8

15.0

24.8

6.1

20.0

4.1

15.0

14.7

12.3

8.4

11.6

7.3

8.3

12.6

19.2

19.0

20.1

4.1

9.4

8.2

13.3

27.9

30.7

36.8

13.0

...

...

.6

_

_

7.4

8.9

1.4

14.9

5.3

...

...

 -

6.2

..-

11.2

1.6

.7

2.5

4.1

2.1

8.5

4.1

10.1

5.5

16.9

52.3

24.3

47.8

38.5

18.6

31.1

3.4

12.1

18.6

32.3

24.3

32.6

26.1

11.4

35.9

32.1

38.7

32.6

18.7

38.3

15.3

34.3

30.1

35.6

31.7

38.4

27.6

16.7

7.5

10.6

1.9

1.8

8.2

2.1

.5

5.0

8.7

14.6

14.6

6.1

1.2

6.5

.8

.5

11.6

6.8

6.9

1.9

1.3

9.9

1.4

.6

5.1

.6

9.9

6.2

2.3

3.3

2.2

1.1

.7

31.8

54.1

32.5

49.9

39.0

19.7

39.8

18.0

34.1

33.6

.9

30.8

33.4

41.5

28.3

42.7

39.0

40.6

33.9

34.8

39.7

27.1

41.0

31.4

39.0

42.0

44.8

39.4

23.0

18.7

16.8

44

40

40

40

38

40

38

38

38

47

42

35

38

29

32

48

32

44

47

47

47

32

38

33

38

55

31

35

48

32

38

...

...

...

43

50

45

49

44

_

48

37

40

45

51

52

52

...

40

36

41

61

32

39

51

...

39

...

...

38

30

37

32

32

_

36

28

21

36

41

40

43

25

24

24

44

29

26

41

33

Hypidiomorphic.

Hornfelsed.

Protoclastic.

Xenomorphic.

Hypidiomorphic.

Do.

Do.

Do.

Do.

Xenomorphic

Seriate; xenomorphic.

Xenomorphic; seriate.

Hypidiomorphic.

Protoclastic.

Xenomorphic.

Do.

Do.

Hypidomorphic.

Xenomorphic.

Do.

Protoclastic.

Hypidiomorphic.

Hypidiomorphiccataclastic.

Protoclastic.

Xenomorphic.

Hypidiomorphic.

Xenomorphic.

Protoclastic.

Do.

Do.

Quartz diorite augen gneiss

11

20

26

27

28

32

33

34

35

39

40

42

43

44

46

47

48.2

49.1

48.8

44.2

30.8

36.8

39.7

40.5

42.1

48.2 1.0

45.5 .4

41.6 .9

34.6 .7

43.7 .2

52.4 .6

48.4 1.9

35.8

26.5

21.8

36.1

48.3

36.7

41.1

40.1

45.7

30.4

40.6

34.5

54.7

45.1

27.4

37.0

7.1

3.1

4.0

4.2

7.1

.9

2.9

2.2

_

4.2

3.9

.--

3.6

3.5

...

18.3

23.3

14.6

11.9

25.9

18.1

17.0

7.1

16.8

10.9

16.1

...

7.9

13.2

7.3

8.9

3.0

2.1

1.9

1.9

.6

1.1

1.5

2.2

1.4

2.6

2.7

6.1

3.1

2.8

.2

16.0

24.4

29.4

20.7

20.9

26.5

19.2

19.4

12.2

20.4

13.5

23.0

10.0

11.0

19.6

11.0

37

38

38

45

31

43

45

36

35

33

33

32

33

36

33

42

45

53

49

35

28

35

33

32

35

29

...

38

35

44

24

35

36

28

40

50

38

39

23

49

34

29

38

Protoclastic.

Hypidiomorphiccataclastic.

Hypidiomorphic.

Xenomorphicprotoclastic.

Protoclastic.

Reversed zoning of

plagioclase; hypidiomorphic.

Reversed zoning of

plagioclase; protoclastic.

Protoclastic.

Do.

Reversed zoning of

plagioclase; protoclastic.

Protoclastic.

Reversed zoning of

plagioclase; seriate;

xenomorphic.

Protoclastic.

Do.

Porphyroclastic.

Xenomorphic; protoclastic.

Hornblende quartz diorite gneiss

2

3

6

7

8

10

12

16

25

42.9

44.3

33.5

47.5

41.6

42.7 0.3

37.4 .1

46.7

48.5

23.6

27.1

19.5

6.4

24.8

24.1

24.2

14.7

9.0

...

.-.

6.9

2.4

8.9

...

.8

4.9

...

42.9

21.8

26.9

42.2

18.6

25.6

26.0

21.0

36.8

2.2

6.8

13.2

1.5

6.1

7.3

5.5

12.7

5.7

45.1

28.6

47.0

46.1

33.6

32.9

32.3

38.6

42.5

38

42

55

46

40

58

40

38

49

40

46

...

51

44

60

45

40

65

33

29

36

38

47

33

33

35

Xenomorphic.

Do.

Porphyroclastic.

Hypidiomorphic.

Protoclastic.

Xenomorphic.

Hypidiomorphic.

Xenomorphic.

Do.
14 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 3. Chemical and spectrographic analyses and norms of rock samples from the Dumbell Mountain plutons, central Washington

[For samples 1-5, 7, and 8, Si02 , A1ZO3 , and TiO2 determined colorimetrically; total Fe, MgO, CaO, and MnO determined by atomic absorption; FeO determined titremetrically; Naz O and 

K2 O determined by flame photometer; analysts: G. T. Burrow, Wayne Mountjoy, H. H. Lipp, and Johnnie Gardner. For samples 6 and 9, rapid rock analyses by P. L. D. Elmore, K. E. 

White, and S. D. Botts. Spectrographic analyses by B. W. Lanthorn and K. E. Valentine. <, less than; N.d. -;ot determined; leaders (- - -), below level of sensitivity]

..... i 2 3 4 5 6 7 8 9

Chemical analyses (percent)

Si02 -----------

AlaOs-----------

Fe2 03 ----------

FeO - - -

MgO-----------

PaO

Na2O-----------

K c\

T;r»

P

f\

MnO-----------

H c\

rif\

Total-------

d n

n

o

1

C

o in

----- 7.2

an

----- N.d.

----- .11

----- N.d.

----- N.d.

----- 100

62.4 

17.5 

1.8 

4.20 

3.04 

6.5 

3.85 

.79 

.73 

N.d. 

.10 

N.d. 

N.d.

101

63.8 

17.1 

1.6 

3.14 

2.48 

5.7 

4.06 

1.03 

.56 

N.d. 

.08 

N.d. 

N.d.

100

70.8 

15.4 

1.4 

2.46 

1.46 

5.2 

3.88 

.11 

.45 

N.d. 

.09 

N.d. 

N.d.

101

73.7 

15.0 

.9 

2.79 

1.23 

4.1 

3.52 

.68 

.41 

N.d. 

.06 

N.d. 

N.d.

102

68.9 

14.3 

2.1 

2.6 

1.7 

4.7 

3.5 

.42 

.41 

.21 

.11 

.76 

< .05

100

52.5 

20.9 

2.0 

6.45 

3.67 

11.1 

2.74 

.23 

.93 

N.d. 

.13 

N.d. 

N.d.

101

65.7 

16.2 

1.2 

3.87 

2.63 

7.1 

3.59 

.24 

.71 

N.d. 

.10 

N.d. 

N.d.

101

56.9

17.9 

2.7 

4.2 

3.7 

7.3 

3.4 

.66 

.59 

.24 

.14 

1.5 

< .05

99

Semiquantitative spectrographic analyses (parts per million)

Ba --------------

Be --------------

Co --------------

Cr --------------

CU --------------

Ni -------.----..

Pb ----------.-..

Sc --------------

Sr --------------

V ------------.-.

Y ---------------

Zr --------------

Ga -

Yb --------------

o.nn

on

..... 15

..... 15

on

..... 10

o.n

7nn

..... 150

on

50

o.n

700

20 

30 

30 

20

30 

1,000 

200 

30 

100 

30 

3

700

20 

30 

15 

15 

10 

30 

1,000 

150 

30 

70 

30 

3

150

10 

5 

3 

5

30 

200 

150 

30 

150 

20 

7

300

15 

10 

5 

5

20 

200 

100 

30 

200 

30 

5

30

10 

3 

10

10 

300 

10 

10 

10 

10 

1

200

30 

30

70 

15

70 

300 

300 

30 

30 

30 

3

150

15 

5 

15 

15

30 

500 

150 

30 

30 

15 

5

100 

30 

30 

10 

30

10 

1,000 

10 

10 

10 

30 

1

Norms

q ...............

flh

di-~-~ ------

hy ----- -...

il ...............

Total--------

---- 17.05

o 07

OQ no

Q1 CO

3

/tc

.... 1 1 qq

2

QO

.... 1 07

---- 100.00

16.91 

4.63 

32.26 

27.88 

3.32 

11.04 

2.59 

1.37

100.00

19.40 

6.11 

34.49 

25.51 

2.35 

8.74 

2.33 

1.07

100.00

33.16 

.64 

32.40 

23.99 

1.22 

5.74 

2.01 

.84

100.00

37.40 

3.92 

29.07 

19.86 

6.72 

1.00 

1.27 

.76

100.00

34.25 

2.51 

29.89 

21.84 

6.87 

.17 

3.08 

.79 

.60

100.00

4.75 

1.35 

23.02 

43.76 

9.03 

13.45 

2.88 

1.76

100.00

23.83 

1.40 

29.96 

27.02 

6.34 

8.40 

1.72 

1.33

100.00

12.98 

3.99 

29.40 

32.35 

2.23 

13.22 

4.00 

1.15 

.68

100.00

Plagioclase composition 

52.1 46.4 42.5 42.5 40.6 42.2 65.5 47.4 52.4
PRE-TERTIARY INTRUSIVE ROCKS 15

TABLE 3. Chemical and spectrographic analyses and norms of rock samples from the Dumbell Mountain plutons, central WashingtonContinued

Sample descriptions

1. Composite sample

2. Composite sample

3. Composite sample

4. Composite sample

5. Composite sample

6. Composite sample

7. Hornblende-quartz

8. Hornblende-quartz

9. Composite sample

of gneissic hornblende-quartz diorite; composition of plagioclase about An**, to An48.

of gneissic hornblende-quartz diorite; composition of plagioclase about An3 8.

of gneissic hornblende-quartz diorite; composition of plagioclase about Ans2.

of hornblende-quartz diorite augen gneiss; composition of plagioclase about An45.

of hornblende-quartz diorite augen gneiss; composition of plagioclase about Ansg.

of hornblende-quartz diorite augen gneiss; composition of plagioclase An3g to AtU4.

diorite gneiss; composition of plagioclase about An5o.

diorite gneiss; composition of plagioclase about An3 s.

of hornblende-quartz diorite gneiss; plagioclase of various compositions.

21

Plagioclase

Potassium 

feldspar

EXPLANATION

 52 Gneissic hornblende-quartz diorite 

A12 Hornblende-quartz diorite

augen gneiss 

n 47 Hornblende-quartz diorite gneiss

FIGURE 11. Plot of modes of rock samples from the Dumbell 

Mountain plutons, central Washington, on a quartz-potassium 

feldspar-plagioclase diagram. Sample analyses are given in table 2.

The amount of mafic minerals, mostly hornblende, 

averages about 35 percent but ranges from 10 to 45 percent (table 2).

The microtexture ranges from hypidiomorphic to 

xenomorphic with varying degrees of protoclastic 

modifications. In general, however, the quartz diorite 

gneiss is the least protoclastic of the Dumbell Mountain 

rocks, and foliation seems to be largely a result of

Quartz

Potassium 

Plagioclase 5 35 feldspar

EXPLANATION

 Dumbell Mountain plutons

A2 Bearcat Ridge plutons

D^ Leroy Creek pluton

FIGURE 12. Plot of norms of rock samples from the Dumbell 

Mountain, Bearcat Ridge and Leroy Creek plutons, central 

Washington, on a quartz-potassium feldspar-plagioclase diagram. 

Sample analyses are given in table 3 (Dumbell Mountain), table 5 

(Bearcat Ridge), and table 7 (Leroy Creek).

flowage and of crystallization under stress, but of 

generally insufficient stress to produce the extensive 

protoclasis so evident in the other Dumbell Mountain 

rocks.

The chemical composition of the hornblende-quartz 

diorite gneiss appears to be somewhat more variable 

than is true of the other Dumbell Mountain rocks, 

despite its generally more uniform appearance (table 3).
16 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

UJ

o tc

UJ 

0_

g

UJ

to

UJ

g

X

o

EXPLANATION

o Bearcat Ridge plutons

A Leroy Creek pluton

 Dumbelt Mountain plutons

EXPLANATION

 Seven-fingered Jack and

Entiat plutons 

A Tenpeak and White

Mountain plutons 

o Quartz diorite of High Pass

25

20

C?

15

10

5

co

9,

V

u0

10

§ 

0

5

9,

s

0 

 

*

9 o o

1 1

r ~~

. o

 »* A

1 * | 0 

o Quartz diorite of Cardinal Peak

20

CO

9, IB

5j

10 

10

co 

9, ^5s

u.

1 

~ 

c 0

o » 

1 t °

[- 

 

o 

<(> 0 A

0 

5

OV

u.

0 

10

Q

w 5

10

oto 5

O

0

5

9i a1 

z

0

5

9i

~ »

,

 

o 

~~ 0 0 0 A ~~

 * * 

1 1

r n

o

1 . . A.

0 

10

O

(J

!_ I

0

9 A A ° O

I

- 

 .

A A O O

I Io

 A 

 .A 

0 0

O

I I

 

 A

 A

| 0 0 | 0

_

A 

 0 

O

O

o I

5

9i

~ o o o ~

A «A

o I I

3 T. .... o o . -|

0 -- u 

g !r . * ,.~i g T ^ - io "i

50 60 70 50 

SiO2, IN WEIGHT PERCENT

60 70

FlGURElS. Variation diagrams of major oxides in analyzed rock samples from pre-Tertiary plutons, central Washington.
PRE-TERTIARY INTRUSIVE ROCKS 17

FIGURE 14. Hornblende-quartz diorite gneiss from the Dumbell 

Mountain plutons, central Washington. Thin section shown in 

figure 9.

As is true of all the Dumbell Mountain rocks, the 

hornblende -quartz diorite gneiss is remarkably low in 

K2O for a rock of otherwise unremarkable composition. 

A possible reason for the paucity of K2O is discussed in 

the section on "Composition and differentiation."

HORNBLENDE-QUARTZ DIORITE AUGEN GNEISS

The pluton of hornblende-quartz diorite augen gneiss 

extends south-southeastward from near the outlet of 

Holden Creek to about the junction of Ice Creek and the 

Entiat River, a distance of about 15 km. Unlike the other 

Dumbell Mountain plutons, this one contains some 

screens of hornblende schist and gneiss a kilometer or 

two long, much larger than the small and unmapped 

sheets that occur in the others. Much of the eastern contact of this pluton has been intricately intruded by dikes 

satellitic to the late Eocene Duncan Hill pluton and 

these dikes furnished part of the material that forms the 

contact complex surrounding the northern end of the 

Duncan Hill pluton.

Most of the rock is characteristically an augen gneiss 

(fig. 7), the augen consisting of nearly pure aggregates of 

plagioclase and quartz or mixtures of both; more rarely 

an augen may consist of a single abraded grain of 

plagioclase. Unlike the hornblende-quartz diorite gneiss, 

the foliation of the augen gneiss is swirled in many places 

and attitudes vary greatly over short distances. Inclusions are numerous in the augen gneiss; many show little 

effect of immersion in the quartz diorite magma, but 

others have been almost completely assimilated and are 

barely distinguishable from the surrounding augen 

gneiss. Many are extremely flat and attenuated, particularly on Spectacle Buttes where we found one only 1 

to 3 cm thick and 13 m long. Most of these consist almost 

entirely of hornblende. Great numbers of inclusions have 

dark, hornblende-rich margins from which felsic 

minerals have been almost completely removed (fig. 7) .

Long dimensions of most inclusions parallel foliation of 

the augen gneiss, but some are discordant.

Study of thin sections showed the augen gneiss to be 

mineralogically almost identical to the hornblendequartz diorite gneiss, including the same range of compositions of the plagioclase. The texture, however, differs 

considerably in that the augen gneiss is everywhere 

protoclastic and in most places decidedly so, although 

the range of protoclasis is from extreme to mild. In 

gradational contact zones and where screens and inclusions of metamorphic rock are numerous, textures range 

from metamorphic in the inclusions to protoclastic in the 

intrusive material; in fact, because some of the augen 

gneiss closely resembles some varieties of the host 

metamorphic rocks, only by thin-section examination 

can distinctions be made, or, for that matter, can the 

augen gneiss and metamorphic rocks be distinguished 

from much of the contaminated or granitized rock of the 

gradational contacts. Plagioclase is most profoundly affected by protoclasis, and in many thin sections is the 

only mineral to show the effects of grinding. Quartz 

characteristically forms lentils consisting of a mosaic of 

interlocking grains, but small quantities are interstitial 

or replace earlier minerals, mostly plagioclase. Where 

present, biotite most commonly occurs with the quartz 

lentils. The relationship of quartz lentils and biotite to 

the rest of the rock suggests that these late constituents 

were squeezed or filter pressed when still fluid from the 

mass of crystals being milled during intrusion.

The hornblende-quartz diorite augen gneiss is the 

most siliceous of the Dumbell Mountain rocks (table 3) 

but shares with the other varieties an extraordinarily low 

content of K2O.

GNEISSIC HORNBLENDE-QUARTZ DIORITE

Gneissic hornblende-quartz diorite forms the largest of 

the Dumbell Mountain plutons in the mapped area and 

has an outcrop area at least as large as the other 

Dumbell Mountain rocks combined. Younger Sevenfingered Jack intrusive rock nearly splits the pluton 

lengthwise; the western segment is cut off to the north by 

the Miocene Cloudy Pass pluton, but the eastern segment extends an unknown distance north of the Holden 

quadrangle. To the southeast, the pluton narrows and 

either pinches out or is cut off by the Duncan Hill pluton 

beneath the glacial debris and alluvium in the Entiat 

River valley near the Cottonwood Guard Station.

The quartz diorite is mostly medium grained and gray 

and ranges from massive and nearly nongneissic (fig. 15) 

to strongly gneissic. In many places, layers of highly 

foliated or gneissic rock a few centimeters to a few meters 

thick alternate with layers of nearly structureless rock. 

Swirled foliation is a common feature, probably even 

more so than in the hornblende-quartz diorite augen
18 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

FIGURE 15. Gneissic hornblende-quartz diorite, a less gneissic facies, 

from the Dumbell Mountain plutons, central Washington.

gneiss. Locally inclusions are common, but nowhere are 

they as attenuated as are some of those in the 

hornblende-quartz diorite augen gneiss.

In thin section, gneissic hornblende-quartz diorite is 

seen to be mineralogically identical to other Dumbell 

Mountain rock, except that considerable quantities of it 

contain sodic andesine averaging about An.32 , but 

medium or calcic andesine still predominates. Textures 

range from hypidiomorphic through xenomorphic to 

protoclastic. Much is also cataclastic, especially near 

shear zones. The more gneissic varieties are more highly 

protoclastic, and in the interlayered gneissic and nongneissic rocks, the gneissic layers are protoclastic.

The chemical composition of the gneissic hornblendequartz diorite is apparently more uniform than is the 

composition of the other Dumbell Mountain rocks, but 

the content of K20 is characteristically low (table 3).

BEARCAT RIDGE PLUTONS

The Bearcat Ridge plutons crop out in the Lucerne 

quadrangle between Lake Chelan and Railroad Creek. 

The larger of the two plutons has a length west of Lake 

Chelan of about 18.7 km and a maximum width of nearly 

1.25 km. It is cut off to the north and northwest by the 

Railroad Creek and Cardinal Peak plutons. The smaller 

pluton has a length of about 4.8 km and a maximum 

width west of Lake Chelan of about 1.2 km. How far 

either pluton extends east of the lake, if at all, is 

unknown.

Both plutons are of granodiorite and quartz diorite 

and are roughly conformable to enclosing metamorphic 

rocks but locally crosscut them, particularly where they 

are isoclinally folded. None of the observed contacts,

however, were discordant within the limits of the outcrops examined. The smaller pluton and the prong of the 

larger one that cuts across the headwaters of Bear Creek 

have wedged the host rocks apart and, in fact, may have 

been responsible for the tight and complex folding of the 

host rocks in the area. All contacts are either sharp or 

gradational through a zone only a few centimeters thick. 

In some places, however, most noticeably on the spur 

ridge between Klone and Tumble Creeks, the contact 

was difficult to locate precisely because the highly 

protoclastic, fissile border rocks of the pluton so closely 

resemble the sheared, highly fissile enclosing gneisses of 

similar composition.

Rocks of the Bearcat Ridge plutons are of variable appearance and composition, all are gneissic or foliated to 

some degree, and all are nearly white to dark gray, 

depending on the content of mafic minerals and the 

grain size. Most abundant are medium-grained, gray 

rocks verging on augengneiss (fig. 16). The plagioclase 

forms porphyroclastic eyes or thin lenses, around which 

are wrapped thin folia consisting of aggregates of biotite 

and hornblende crystals. Intermingled with these gray 

rocks are rather large quantities of light-colored gneiss 

that form conformable lenses and anastomosing dikes 

rarely more than several centimeters thick; the dikes intrude more or less aimlessly the darker rocks. Contacts 

between the normal and the light-colored facies are 

gradational, and attitudes of foliation cross the light 

facies without deviation. Foliation, however, is much 

less distinct in the lighter rocks. Dark facies also occur 

but are much rarer than the light facies and seem to be 

more common near contacts. Some of the darker rocks 

are actually more mafic, but most, particularly those 

near contacts, are merely finer grained and lack the

t / 

,.

FIGURE 16. Protoclastic biotite-hornblende-quartz diorite gneiss from 

the Bearcat Ridge plutons, Lucerne quadrangle. Dike is Tertiary 

granodiorite.
PRE-TERTIARY INTRUSIVE ROCKS 19

degree of segregation into felsic and mafic folia of rocks 

farther from contacts.

The larger pluton consists mostly of hornblendebearing rocks that range in composition from biotitehornblende granodiorite to quartz diorite, but some 

hornblende-free rocks also occur. Granodiorite shown in 

figure 17 is typical of the less gneissic rocks. The smaller 

pluton is almost, but not entirely, devoid of hornblendic 

rocks and consists of biotite granodiorite and quartz 

diorite. Figure 18 illustrates a nearly nongneissic facies 

of granodiorite. As a general rule, hornblendic rocks 

seem to be slightly older and are intruded by rocks containing only biotite, but contacts between the two types 

of rock are mostly gradational in places through many 

meters. The field relations suggest that both types were 

mobile simultaneously. Because of the similarity of appearance, the difficulty in recognizing rocks containing 

no hornblende (hornblende is commonly much subordinate to biotite in any case), and the erratic distribution of the two types, no effort was made to separately 

delineate them in either of the two plutons.

Thin-section examination of the rocks reveals many 

characteristics that are common to all rocks in the 

plutons, the most striking of which is the pervasive 

protoclasis that lends to the rocks their gneissic appearance, but there are also some significant differences 

between rock types. Hornblende-bearing rocks contain 

considerable ilmenite and coarse titanite, and plagioclase has an average composition of about An3 3, whereas 

rocks lacking hornblende contain very little titanite, no 

ilmenite, and plagioclase has an average composition of 

about An2o. All the rocks contain varying quantities of 

quartz, biotite, and orthoclase, along with accessory 

magnetite and apatite. North of Graham Harbor Creek, 

near the southwest contact of the smaller pluton, the 

rock not only contains biotite but also considerable

FIGURE 17. Hornblende-biotite granodiorite gneiss from the Bearcat 

Ridge plutons, Lucerne quadrangle.

FIGURE 18. Biotite granodiorite from the Bearcat Ridge plutons, 

Lucerne quadrangle.

muscovite. A little chlorite was seen in all sections as an 

alteration product of the mafic minerals, especially 

biotite, and some epidote occurs in a few thin sections. 

Andesine in the hornblende-bearing rocks and oligoclase 

in the hornblende-free rocks occur as abraded, rounded, 

and commonly fractured porphyroclasts. These 

porphyroclasts may have tails of abraded material 

streaming away from them, but most commonly, the 

abraded material forms a mortar surrounding the 

porphyroclasts. A few porphyroclasts, in most sections, 

show faint oscillatory and patchy zoning, attesting 

thereby to their igneous origin. Myrmekite showing a 

variety of forms is rather common. Quartz occurs as interstitial anhedral grains in the least deformed rocks, 

but by far the greatest amount occurs as thin, lenslike 

folia consisting of mosaics of interlocking crystals; these 

folia commonly occur in the zones of granulated 

plagioclase. Orthoclase, much of it perthitic, is commonly interstitial or is associated with the quartz folia, 

but some partly replaces both granulated and 

porphyroclastic plagioclase. Some of the larger grains of 

orthoclase are traversed by zones of perthite that follow 

lines of distortion in the grains. The amount of 

orthoclase ranges between rather wide limits; some of 

the biotite-hornblende quartz diorites contain less than 1 

percent, whereas some of the leucocratic material may 

contain as much as 50 percent, but most rocks contain 

between 5 and 15 percent. Rocks containing sufficient 

orthoclase to be called granodiorite are at least twice as 

common as the quartz diorites low in orthoclase. The 

distribution of rocks containing more and less orthoclase, however, is haphazard, and in outcrop the rocks 

are indistinguishable. Microcline is rare; accessory 

amounts were seen in only one thin section. The major 

mafic mineral is biotite, and it occurs as folia of anhedral 

shreds that follow planes of granulation. Biotite in all the 

rocks is optically identical, the pleochroic colors ranging
20 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

from straw yellow to dark olive brown. Hornblende, 

where present, usually occurs with biotite, and the 

longer dimensions of the grains are oriented in the plane 

of foliation; in this plane, however, the orientation is 

mostly random, but in a few places a vague lineation is 

apparent. Hornblende is anhedral and pleochroic from 

yellowish green to dark green. Biotite tends to replace 

hornblende, and hornblende adjacent to biotite is 

generally lighter colored. Titanite is a common accessory 

in the hornblendic rocks; much of it forms rhombs as 

long as 1 mm, but some forms irregular rims surrounding 

grains of ilmenite.

The most characteristic feature of the Bearcat Ridge 

rocks is their pervasive protoclastic texture. As a rule, all 

the minerals show some slight distortion, i.e., undulatory extinction in quartz and warping of scattered 

biotite and hornblende grains, but only plagioclase, the 

earliest formed mineral, has everywhere undergone intensive and extensive grinding. No grains have escaped 

abrasion entirely, and many porphyroclasts consist of 

slightly rotated fragments of an original crystal. The undistorted or only slightly distorted later minerals

 hornblende, biotite, quartz, and potassium feldspar

 that grew along planes of granulation, indicate that by 

the time they started crystallizing, the plutons had 

largely come to rest. The leucocratic lenses and dikes 

that are so common throughout the plutons and, indeed, 

cut the enclosing metamorphic host rocks are probably 

the results of this process of squeezing and grinding. The 

plagioclase in these lighter rocks is identical to the 

plagioclase of the surrounding granodiorites and quartz 

diorites and show the same abraded outlines, but they

form a relatively small proportion of these lighter rocks, 

which consist largely of quartz and orthoclase. Thus, the 

still-fluid component that was to crystallize mostly as 

quartz and orthoclase seems to have been filter pressed 

from the crystal mush of the intruding plutons to form 

these leucocratic lenses and dikes. Directed stresses had 

not entirely ceased, however, by the time the leucocratic 

rocks crystallized. This is indicated by the rocks' vague 

foliated texture defined by the parallel orientation of the 

biotite, in places parallel to the walls of the dike but 

elsewhere parallel to the regional attitudes of enclosing 

rock regardless of orientation of dikes.

Modal analyses of the Bearcat Ridge plutons are given 

in table 4, and chemical analyses in table 5. Figure 19 

shows the locations of modally analyzed specimens, and 

figure 20 is a plot on a triangular diagram of these 

modes. A plot of the norms is given in figure 12, and a 

variation diagram of major oxides in figure 13.

LEROY CREEK PLUTON

The Leroy Creek pluton, a mass of gneissic biotitequartz diorite about 10 km long and 2 km wide, extends 

along the west side of the Entiat Mountains from upper 

Rock Creek to upper Phelps Creek. The pluton intrudes 

Dumbell Mountain gneissic hornblende-quartz diorite 

and is in turn intruded by quartz diorites of the Sevenfingered Jack plutons; hence, the ages of 45 and 54 m.y., 

determined on mica (Engels and others, 1976) are much 

too young and indicate heating by later intrusions.

The Leroy Creek pluton consists of fine- to mediumgrained gneissic biotite-quartz diorite (fig. 21). The rock

TABLE 4. Modal analyses of samples of quartz diorite and granodiorite gneiss from the Bearcat Ridge plutons, Lucerne quadrangle

[Leaders (- - - ), not measured or not present]

Sample 

No.

1

2 

3

4

5

6

7

8

9

10

11

12

13

14

15

Plagioclase

54.5

46.4 

53.9

41.8

47.1

55.7

67.6

54.5

55.2

56.8

55.0

55.9

44.2

36.4

50.1

Potassium 

feldspar

0.4

10.6 

9.1

11.8

8.5

7.8

1.7

3.4

6.8

4.1

6.2

13.2

15.7

33.3

12.3

Quartz

18.0

12.8 

14.2

3.2

18.7

19.4

13.8

23.4

18.2

19.2

30.4

21.0

30.2

25.1

30.8

Biotite

11.2

2.8 

9.7

11.0

13.7

6.7

6.8

16.6

9.4

6.2

7.9

9.0

7.6

4.5

6.3

Hornblende

14.5

23.0 

10.8

3.1

10.7

8.2

5.5

1.3

9.7

12.6

_

...

Accessory 

and secondary minerals

1.4

4.4 

2.3

1.1

1.3

2.5

4.6

.8

.7

1.1

.5

.9

2.3

.7

.5

Total 

mafic 

minerals

27.1

30.2 

13.1

15.2

25.7

17.4

16.9

18.7

19.8

19.9

8.4

9.9

9.9

5.2

6.8

Anorthite in 

plagioclase crystals (percent)

Average

40

33 

33

29

32

32

35

32

28

27

25

23

23

22

24

Core

35 

40

33

33

_

32

29

26

27

27

23

Rim

31

26

28

29

_

25

25

23

15

16

18

Remarks

Protoclastic.

Do. 

Xenomorphic.

Protoclastic.

Do.

Xenomorphic; sphene

rimmed with

ilmenite.

Xenomorphic.

Do.

Protoclastic.

Xenomorphic; slightly

protoclastic.

Protoclastic.

Xenomorphic.

Some muscovite;

hypidiomorphic- protoclastic.

Xenomorphicprotoclastic.

Protoclastic.
PRE-TERTIARY INTRUSIVE ROCKS 21

TABLE 5. Chemical and spectrographic analyses and norms of rock \ 

samples from the Bearcat Ridge plutons, Lucerne quadrangles

[For samples 1 and 3, standard rock analysis by E. E. Engleman. For sample 2, SiO2 and A12O3 

determined colorimetrically; FeO determined volumetrically; Fe2O3 , MgO, CaO, and Mn 

determined by atomic absorption; Na2O and K2O determined by flame photometer; 

analysts: Violet Merritt, Wayne Mountjoy, J. D. Mensick, Claude Huffman, H. H. Lipp, G. 

T. Burrow, and G. D. Shipley. Spectrographic analysts: Barbara Tobin, H. G. Neiman, and 

B. W. Lanthorn. N.d., not determined; leaders (- - -), below sensitivity limit; N.p., not 

present]

Sample--------------- 123

Chemical analyses (percent)

Si02 ----------------- 71.25 69.8 65.7

A12O3 ----------------- 15.99 16.2 17.1

Fe2O3 ---------------- .45 3.14 1.12

FeO------------------ 1.06 1.00 2.68

MgO ----------------- .52 .48 1.3

CaO ----------------- 2.44 2.12 4.3

Na2O----------------- 4.79 4.77 4.53

K2O------------------ 2.55 1.83 1.96

H2O+---------------- .29 N.d. N.d.

H2O- ---------------- .02 N.d. N.d.

TiO2 ----------------- .23 N.d. N.d.

P2 05 ----------------- .07 N.d. N.d.

MnO----------------- .04 .04 .076

CO2 ------------------ .00 N.d. N.d.

Cl ------------------- .00 N.d. N.d.

F -------------------- .04______N.d.______N.d.

Subtotal---------- 99.74

LessH2O --------- .02

Total------------- 99.72 99 99

Semiquantitative spectrographic analyses (parts per million)

B -------------------- 20

Ba ------------------- 1,000 500 1,000

Be ------------------- 1

Co ------------------- 15

Cr ------------------- 5 1 50

Cu------------------ 

Ga ------------------- 30 

355

30 20

Nb------------------- 10

Ni ------------------- 20

Pb ------------------- 70 15

Sc ------------------- 5 15 15

Sr ------------------- 1,000 500 1,000

V-------------------- 30 20 100

Y -------------------- 10 10

Yb------------------- 

Zr ------------------- 100 

111

70 50

Norms

q ....---...-.--....-. 27.51 30.00 19.24

or-------------------- 15.13 10.88 11.72

ab ------------------- 40.68 40.59 38.79

an ------------------- 11.40 10.58 20.80

hy ------------------- 2.57 1.20 .66

c--------------------- .120 2.34 7.14

mt ------------------- .65 3.38 1.65

il .................... .44 .83 N.p.

ap ------------------- .17 N.p. N.p.

Total------------- 100.00 100.00 100.00

TABLE 5. Chemical and spectrographic analyses and norms of rock 

samples from the Bearcat Ridge plutons, Lucerne quadrangles 

Continued

Sample------------- 123

Plagioclase composition

21.9 20.7 34.9

Sample descriptions

1. Composite sample of biotite granodiorite gneiss.

2. Composite sample of hornblende-biotite-quartz diorite gneiss.

3. Composite sample of biotite-hornblende-quartz diorite gneiss.

120°30'

5 KILOMETERS

FIGURE 19. Map showing location of modally analyzed samples from 

the Bearcat Ridge plutons, Lucerne quadrangle. Sample analyses 

are given in table 4.

varies considerably in appearance from place to place; 

most of it is rather light colored, but where contaminated with considerable mafic material derived 

from host rocks of hornblende and biotite gneiss and 

schist, it is dark. Some of it is nearly nonfoliated and 

medium grained, whereas at the other extreme rocks are 

so finely foliated as to appear almost schistose. Probably 

the most characteristic feature of the rock is the pervasive swirled foliation. This foliation, defined mostly by 

planar parallelism of biotite flakes, trends generally 

northwest, but at the north end of the pluton, trends are 

northeast more or less parallel to the contact. 

Everywhere, however, are local changes in trends 

swirls on scales ranging from a few meters to many tens 

of meters. As with other gneissic intrusive rocks in the 

area, the foliation is the result of pervasive protoclasis, 

but here the foliation is generally far more highly swirled
22 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Quartz

Piagioclase

.14

35

Potassium 

feldspar

FIGURE 20. Plot of modes of rock samples from the Bearcat Ridge 

plutons, Lucerne quadrangle, on a quartz-potassium feldsparplagioclase diagram. Sample analyses are given in table 4.

FIGURE 21. Gneissic biotite-quartz diorite from the Leroy Creek 

pluton, Holden quadrangle.

than in other plutons, indicative, perhaps, of more irregular movement of the crystal-packed magma during 

intrusion than seems to have been true in other plutons. 

Despite the variability of appearance, the composition 

of the Leroy Creek pluton is rather uniform except for 

the hornblende-bearing rocks at the north end. The 

hornblende-free rocks consist of 48 to 58 percent 

oligoclase, 33 to 37 percent quartz, and 5 to 11 percent

biotite as essential minerals, and epidote, sericite, and 

chlorite in generally small but variable quantities as 

secondary minerals (table 6). Potassium feldspar, 

opaque minerals, titanite, muscovite, and apatite are accessory. In the northern part of the pluton, garnet 

crystals as much as 1 cm across are fairly common.

As with other quartz diorite plutons in the study area, 

the Leroy Creek pluton also contains many inclusions of 

hornblende gneiss and schist and Swakane Biotite 

Gneiss. Relicts of Swakane are less obvious than 

hornblendic inclusions because of the similarity of the 

Leroy Creek gneissic quartz diorite to the Swakane. 

Inclusions of Swakane tend to form ghostlike wisps and 

streaks and larger irregular masses that grade into 

quartz diorite, whereas inclusions of hornblende gneiss 

and schist mostly form long, thin layers having sharp 

contacts with the enclosing quartz diorite. Scattered 

dark, angular, unoriented inclusions do occur, however, 

and are largely restricted to the swirled facies of the rock.

Contacts of the Leroy Creek pluton are mostly rather 

abrupt, the lateral contacts commonly consisting of thin 

zones of lit-par-lit injections. The northwest end is 

marked by a zone of migmatite a few meters thick, and 

here gneissic quartz diorite contains considerable 

hornblende in contrast to the rock elsewhere in the 

pluton. The pluton has had little megascopically discernible effect on the enclosing wall rocks.

Piagioclase is medium oligoclase in the hornblendefree rocks but ranges up to sodic andesine in the 

hornblendic rocks at the north end of the pluton. 

Piagioclase is mostly anhedral and unzoned, but some 

grains are progressively zoned and a few show 

pronounced oscillatory and patchy zoning. Quartz forms 

anhedral interstitial grains, irregular lenses of interlocking grains, and matrices consisting of mosaics of irregular grains in which plagioclase and other minerals 

occur as partly resorbed islands. Nearly all the quartz is 

strained. Biotite occurs as shreds or aggregates of irregular grains; in some thin sections, biotite is mostly 

confined to zones of granulation. The biotite is 

characteristically olive brown and has been analyzed 

previously (Crowder, 1959, table 2). Hornblende forms 

anhedral blades or aggregates of small blades pleochroic 

in shades of light yellowish brown to green. Most 

clinozoisite-epidote is secondary, but in thin sections 

showing the best hypidiomorphic textures, large subhedral crystals, apparently of primary origin, occur 

separately or with biotite. Such clinozoisite-epidote is 

also characteristic of some other plutons in the study 

area.

Textures of rocks in the Leroy Creek pluton range from 

typically hypidiomorhpic to xenomorphic and protoclastic. Some of the rock is slightly recrystallized. Most 

characteristic are xenomorphic textures with subdued 

protoclastic modifications. Piagioclase grains show con-
PRE-TERTIARY INTRUSIVE ROCKS 23

TABLE 6. Modal analyses of samples of biotite-quartz diorite gneiss from the Leroy Creek pluton, Holden quadrangle

[Leade.-s (---), not measured or not present]

Sample

No.

1 

2

3

4

5

6

7

8

9

10

Potassium 

Plagioclase feldspar

40.3 0.2 

47.4

48.7

50.8

48.5

57.2 .2 

53.4

54.3

49.7

41.2

Quartz

48.3 

33.0

36.7

43.8

38.4

33.0 

28.4

38.9

36.6

39.6

Biotite

2.9 

2.2

1.3

9.8

7.1 

3.8

3.6

4.3

1.0

Hornblende

5.4 

13.2

...

.7

...

10.9

...

13.2

Accessory 

and secondary minerals

3.9 

4.2

13.3

4.7

3.3

2.5 

3.5

3.2

9.4

5.0

Total 

mafic 

minerals

12.2 

19.6

14.6

5.4

13.1

9.6 

18.2

6.8

13.7

19.2

Anorthite in 

plagioclase crystals (percent)

Average

28 

30

20

20

23

22 

23

20

22

26

Core

38 

31

27

21

26

27 

30

23

23

31

Rim

16 

26

16

17

21

19 

18

12

15

21

Remarks

Xenomorphic. 

Do.

Do.

Do.

Protoclastic.

Xenomorphic. 

Do.

Protoclastic.

Do.

Xenomorphicprotoclastic.

siderable rounding and some have been broken, and the 

individual fragments have been differentially rotated 

with respect to other fragments. Nevertheless, finegrained comminuted material is mostly rather rare and 

seems to have been resorbed before complete crystallization.

Some of the textures suggest mild recrystallization has 

occurred, but if so, it has been insufficient to destroy the 

swirled foliation indicative of irregular intrusive movements or even to obliterate oscillatory and patchy zoning. Furthermore, there seems little reason to believe 

that granitization was particularly effective in forming 

the pluton, as Crowder (1959) once thought. Repeated 

episodes of large-scale granitization or ultrametamorphism, explaining each successive gneissic pluton 

that otherwise had little effect on the surrounding terrane, seem far less likely than magmas rising 

periodically from the lower crust.

Chemical and spectrographic analyses and norms are 

shown in table 7; locations of modally analyzed 

specimens are shown in figure 22, and a plot of the modes 

in figure 23. A plot of the norms is in figure 12 and a 

variation diagram of major oxides in figure 13.

SEVEN-FINGERED JACK AND ENTIAT PLUTONS

The Seven-fingered Jack and Entiat plutons make up 

a group of intrusions cropping out from the vicinity of 

Hart Lake south-southeastward across the Holden and 

Lucerne quadrangles. The Seven-fingered Jack pluton, 

consisting largely of biotite-hornblende-quartz diorite, is 

the northernmost of these plutons and extends into Ice 

Creek in the Holden quadrangle. The Entiat plutons, 

composing the rest of the plutons, are more variable in 

composition and are directly traceable into the Chelan 

Complex of Hopson (cited in Mattinson, 1972, p. 

3772), and hence they are correlative with that complex. 

Within the two quadrangles, the plutons are closely associated spacially with the Dumbell Mountain and 

Leroy Creek plutons and were considered by Crowder 

(1959) to be genetically related. Mattinson (1972, p. 

3771-3772) also correlated them with these older plutons 

and considered them part of Misch's (1966) 

"Marblemount belt," although he did not rule out 

emplacement during the Jurassic or Early Cretaceous 

(Mattinson, 1972, p. 3378). Although the Seven-fingered 

Jack and Entiat plutons do resemble the Dumbell 

Mountain plutons in many respects, they are compositionally far more diverse, and they not only intrude 

the Dumbell Mountain rocks but contain considerably 

more K^O (tables 3, 8). Ages as determined by Mattinson (1972) are tens of millions of years younger for 

rocks collected from the Chelan Complex. These ages

TABLE 7. Chemical and spectrographic analyses and norms of a 

composite sample of biotite-quartz diorite from the Leroy Creek 

pluton, central Washington

[SiO2 and Al2Oa determined by X-ray fluorescence; total Fe, MgO, and CaO determined by 

atomic absorption; FeO determined volumetrically; Na2O and K2O determined by flame 

photometer; TiOa determined colorimetrically; analysts: P.L.D. Elmore, K. E. White, and 

S. D. Botts. Spectrographic analyses by H. G. Neiman]

Chemical analyses 

(percent)

Semiquantitative

spectrographic 

analysis (parts per million)

SiO2 ------

A12O3 ------

Fe2O3 -----

MgO ------

PaO

Na2O------

K

(-\

rrv/-v

Total ----

----14.0

.... i 24

1 QQ

.... 2 95

- 4 fi4

- - - - 64

1 *\

QO 70

Ba -----------

Cr -----------

Cu-- ------

Mo-----------

cr

V -----------

Y -----------

Zr -----------

Ga- -------

Yb-----------

500 

1.5 

3 

3 

10 

500 

30 

15 

70 

15 

1.5

q --...-.

or---------

hy ........

Total----

O£> f\rj

---- 3.83

QQ 74

----14.82

Q, 1 1

0.9

1 QO

.... 29

---100.00

Plagioclase composition

... 27 2
24 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

121°52'30"

48° | 

10'

121°45'

48° 

05

EXPLANATION

Contact 

2 Sample locality

3 KILOMETERS

FIGURE 22. Map showing location of modally analyzed samples of 

biotite-quartz diorite gneiss from the Leroy Creek pluton, Holden 

quadrangle. Sample analyses are given in table 6.

range from about 100 to 193 m.y. for zircons from samples of these rocks to only 71 to 87 m.y. for sphene from 

the same samples (table 38). Although only one age, a 

Pb207/Pb206 age of 183 m.y. for a medium-grained fraction 

of zircon, was clearly discordant, the Pb207/Pb2u6 ages 

ranging from 100 to 132 m.y. for other samples were 

either concordant or but moderately discordant "within 

the limits of the lead-lead ages" ( Mattinson, 1972, p. 

3778). He considered it likely that these rocks were 

"remobilized" from rocks of the "Marblemount belt," a 

possibility for which little evidence exists. Engels 

(Engels and others, 1976) obtained potassium/argon ages 

of about 60 and 64 m.y. from biotite and hornblende 

from the Entiat pluton, figures that are probably much 

too low because of argon loss. For these reasons, correlations of the Seven-fingered Jack and Entiat plutons with 

the Dumbell Mountain or Leroy Creek plutons are considered erroneous.

The plutons are elongate, narrow masses injected into 

fault zones or zones of structural weakness. None of the 

masses within the mapped area exceeds a thickness of 

about 1.5 km. The largest is the Entiat pluton, consisting of hornblende-biotite- and biotite-hornblendequartz diorite; its length within the mapped area is 

about 16 km, but its total length is not known. The 

Seven-fingered Jack plutons are smaller but more 

diverse in composition, consisting of hornblende-quartz 

diorite and quartz diorite gneiss, hornblende-biotitePiagioclase

Potassium 

feldspar

FIGURE 23. Plot of modes of biotite-quartz diorite gneiss samples 

from the Leroy Creek pluton, Holden quadrangle, on a quartzpotassium feldspar-plagioclase diagram. Sample analyses are given 

in table 6.

and biotite-hornblende-quartz diorite, quartz gabbro, 

diorite, and gabbro. Some of the smaller masses, which 

are merely dikes as little as 30 m or so thick, consist of a 

single rock type. Others, particularly the larger plutons, 

consist of a variety of types, although a single type is 

commonly dominant.

Unfaulted contacts of Seven-fingered Jack plutons are 

mostly sharp where not obscured by later dikes and irregular masses of leucocratic quartz diorite, but locally 

they are gradational through a zone a few meters thick. 

The Entiat pluton, on the other hand, is characterized 

by wild contact complexes, particularly where it cuts 

metamorphic rocks, but the contact is generally sharp 

where intrusive into other plutons. Similar complexes 

characterize the contacts of other quartz diorite plutons 

of different ages in the area; all consist of spectacular 

melanges of various intrusive rocks, inclusions, and 

coarse-grained hornblendite (figs. 24 and 25). In more 

gneissic parts of the complex, foliation laminae wrap 

around inclusions in a manner suggestive of rotation by 

the inclusion because of differential flowage.

BIOTITE-HORNBLENDE-QUARTZ DIORITE

Biotite-hornblende-quartz diorite of the Sevenfingered Jack pluton is mostly a gray, medium-grained 

rock ranging from massive to gneissic (figs. 26, 27). 

Gneissic varieties are erratic in distribution but are
PRE-TERTIARY INTRUSIVE ROCKS 25

FIGURE 24. Coarse- and medium-grained hornblende gabbro from 

contact complex of Entiat pluton, Lucerne quadrangle.

FIGURE 25. Contact complex of Entiat pluton showing pegmatitic 

hornblende gabbro (Hgb), schist (sch), and hornblendite (hdld).

generally more common near contacts; the westernmost 

dikelike mass paralleling the Entiat fault is gneissic 

nearly everywhere. Locally, the large mass between Hart 

Lake and Ice Lakes consists of layers of gneissic quartz

diorite 0.3 m or more thick that alternate with nongneissic rock. Probably the most noteworthy feature of this 

mass, however, is a conspicuous lineation defined by 

closely spaced pencillike mafic streaks and schlieren 

having parallel orientation (fig. 27). In places, the rock 

has a gneissic appearance because of mafic xenoliths 

smeared out in the plane of foliation; angular inclusions 

are common locally.

In thin section, the rock is seen to consist of andesine, 

quartz, and hornblende, and in most specimens, small 

amounts of biotite as essential minerals. Titanite, 

opaque minerals, apatite, and rare zircon are accessory; 

generally small amounts of clinozoisite-epidote, chlorite, 

and sericite occur as secondary products. Andesine 

ranges in average composition from about An38 to nearly 

An50, but most of it falls between An3 s and An45. Crystals 

are subhedral to euhedral and, except where destroyed 

by twinning, show conspicuous oscillatory and patchy 

zoning. In contrast to plagioclase in the Dumbell Mountain plutons, no crystals of which show more than four or 

five oscillations, plagioclase in this quartz diorite commonly shows a dozen or more oscillatory zones. This 

characteristic helps to distinguish rocks of these plutons 

from those of the very similar Dumbell Mountain 

plutons. Quartz is interstitial or replaces andesine and 

hornblende. Hornblende is anhedral to subhedral and 

much of it is zoned, the rims being deeper green than the 

cores. The pleochroic scheme of most of it is X, pale yellow; Y, greenish brown; and Z, dark green or bluish 

green. Cores of some grains contain poikilitic inclusions 

of quartz and smaller amounts of plagioclase. Biotite occurs as irregular flakes or is secondary after hornblende. 

In a few thin sections, clinozoisite-epidote is coarse and 

euhedral and seems to have formed in equilibrium with 

hornblende.

Textures, which in some of the gneissic varieties show 

slight protoclastic modifications, are characteristically 

hypidiomorphic; cracks in crystals of abraded andesine 

are filled with biotite (fig. 28), although most of the rock 

in the westernmost mass is decidedly cataclastic and 

sheared. This mass seems to have been intruded along 

the zone of dislocation marked by the Entiat fault.

HORNBLENDE-BIOTITE-QUARTZ DIORITE

Hornblende-biotite-quartz diorite of the Entiat pluton 

is also a gray rock but is rather more variable in grain 

size than biotite-hornblende-quartz diorite and ranges 

from medium to fairly coarse grained (fig. 29). Locally it 

is gneissic, in places because of protoclasis, elsewhere 

because of alined crystals resulting from flowage. Mafic 

streaks and lenses are common, particularly near contacts. Hornblende-biotite-quartz diorite is microscopically similar to biotite-hornblende-quartz diorite, 

the principal differences being the preponderance of 

biotite over hornblende, generally more sodic
26 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

FIGURE 26. Biotite-hornblende-quartz diorite from Seven-fingered 

Jack pluton, Holden quadrangle.

plagioclase, and the common occurrence of small 

amounts of interstitial potassium feldspar, and in a section or two, enough to classify the rock as granodiorite. 

Characteristic also is considerable titanite as rhombs as 

much as 4 mm long. The textures are hypidiomorphic 

granular with local protoclastic and cataclastic 

modifications.

HORNBLENDE-QUARTZ DIORITE GNEISS

Hornblende-quartz diorite gneiss of the Entiat pluton 

that cuts the southwestern part of the Lucerne 

quadrangle and adjacent parts of the Holden quadrangle 

is a light- to dark-greenish-gray, medium-grained rock 

having a pervasive and highly swirled but not strongly 

accentuated foliation (fig. 30). Light-colored segregation 

dikes and pods are common. Lenticular segregations 

consisting largely of biotite, and other mafic streaks and 

lenses are fairly common and, in places, particularly 

near contacts, angular blocks of amphibolite are 

numerous. Inclusions, except for the angular ones that 

are commonly rotated (fig. 31), are elongated along 

planes of foliation. The rock varies considerably in both 

composition and texture. It consists of calcic oligoclase 

or sodic andesine, quartz, hornblende, and biotite in 

various proportions. Biotite occurs in only accessory 

amounts in most of the rock, but in places it is more 

abundant than hornblende. In lighter colored rocks, 

muscovite is also common. Accessory minerals are 

magnetite, titanite, and apatite. Chlorite and epidoteclinozoisite are secondary. Textures range from 

hypidiomorphic to xenomorphic, variously modified by 

protoclasis and cataclasis (fig. 32).

HORNBLENDE DIORITE AND GABBRO

Hornblende diorite and gabbro of the Seven-fingered 

Jack pluton are confined to the Lucerne quadrangle, 

although small masses of these rocks do occur locally in 

plutons consisting dominantly of the other rock types.

FIGURE 27. Biotite-hornblende-quartz diorite from the Sevenfingered Jack pluton, showing strong lineation defined by pencils of 

mafic-rich material, Holden quadrangle.

The contact complexes do, indeed, consist perhaps 

dominantly of hornblende diorite and gabbro, and along 

the western margin of this diorite-gabbro pluton, the 

contact between the pluton and the complex is 

gradational. The rocks are of varied appearance and 

range from gray to nearly black with a greenish cast and 

from medium to coarse grained, and some are slightly 

pegmatitic. The hornblende diorite is generally of more 

uniform appearance, is gray, medium grained, and 

mostly massive, but some has a slight foliation. Gabbro 

is darker and some is greenish black; grain size, arrangement, and shapes of crystals differ greatly from place to 

place. Some gabbro is rather coarse grained and has a 

panidiomorphic texture; much is medium grained and 

granitoid, but fair quantities are relatively fine grained 

and, in outcrop, are very similar to the pawdite of 

various dikes in the area. The various rock types, including the diorite, are inter gradational and locally 

stirred together in mixtures that look like marble cake.
PRE-TERTIARY INTRUSIVE ROCKS 27

FIGURE 28. Protoclastic hornblende-biotite-quartz diorite from 

Seven-fingered Jack pluton, showing cracks in fractured crystal of 

andesine (A) filled with biotite (B), orthoclase (O), and quartz (Q), 

Holden quadrangle.

Inclusions of various kinds are abundant; among the 

more numerous are knots of hornblendite and clots of 

coarse-grained plagioclase-hornblende rock. Hornblende 

and plagioclase are the only major constituent minerals 

common to all the rocks, but some contain considerable 

biotite and even a few percent of quartz. Plagioclase in 

diorite is calcic andesine and in gabbro is sodic 

labradorite; both oscillating and patchy zoning are common. Orthoclase occurs as a sparse interstitial mineral 

locally, and titanite, apatite, muscovite, and magnetite 

are accessory. Epidote, chlorite, and sericite are secondary. Textures range from xenomorphic to panidiomorphic; both protoclasis and cataclasis are 

prevalent.

CONTACT COMPLEXES

The Seven-fingered Jack and Entiat plutons have the 

largest volume of highly varied contact complexes of any 

intrusive masses in the area. These complexes have the 

same general appearance and contain the same varieties 

of rock types as do the other complexes. Hornblende 

gneiss and schist, inclusions of all orientations, very

FIGURE 29. Hornblende-biotite-quartz diorite from 

pluton, Lucerne quadrangle.

the Entiat

FIGURE 30. Hornblende-biotite-quartz diorite gneiss from the Entiat 

pluton, Holden quadrangle.

coarse grained hornblendite in crystals as much as 15 cm 

long, swarms of dikes and irregular masses of finegrained to pegmatitic hornblende-quartz diorite, diorite, 

and gabbro are mixed together in spectacular melanges. 

The zone extending from Shetipo Creek to Pom as Creek 

is sheared and intruded by swarms of porphyry dikes. 

Mostly, core rocks of the plutons intrude the contact 

complexes, but in scattered outcrops, elements of the 

complex, largely hornblende-quartz diorite and diorite 

but locally gabbro, cut core rocks. In a few places, as for 

example, 1 km south of Larch Lakes, gabbro is chilled
28 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

3^**?!^

I^SCrV % *£«&£> "* lV£

.cT-1 *

FIGURE 31. Rotated inclusions of late Paleozoic gneiss in 

hornblende-quartz diorite gneiss from the Entiat pluton, Lucerne 

quadrangle.

against quartz diorite (fig. 33). In any case, field relations indicate that the rocks of the complexes were certainly at least partly molten when the main masses of 

the plutons were injected. Microscopic examination of 

rocks making up the complexes, particularly the finer 

grained ones, shows that the quartz diorite in them differs little from core rocks of the associated plutons. The 

relation of these contact complexes to the plutons is discussed in a later section entitled "Contact complexes" 

where the general problem of these and contact complexes of other plutons or groups of plutons are considered. It should be stressed, however, that these complexes are devoid of any indication of regional 

metamorphism.

Locations of modally analyzed samples are shown in 

figure 34, modal analyses in table 8, and chemical 

analyses in table 9. A plot of modes is shown in figure 35 

and norms in figure 36. The content of major oxides is 

shown in the variation diagram (fig. 13).

FIGURE 32. Hypidiomorphic and protoclastic hornblende-quartz 

diorite gneiss from the Entiat pluton, Lucerne quadrangle. Note 

slightly rotated fragments of zoned andesine crystal.

LEUCOCRATIC QUARTZ DIORITE AND 

GRANODIORITE

Leucocratic quartz diorite (trondjemite) and granodiorite are the most widespread of the intrusive or 

intrusive-related rocks in the region. Crowd er (1959, p. 

855-862) has described these rocks and their mode of occurrence in detail, and the reader is referred to that 

paper for a more comprehensive treatment of these 

rocks. The interpretation of the genesis and significance 

of these rocks here presented, however, differ in some 

respects to those elucidated by Crowder who believed, at 

that time, that most of the various older intrusive rocks 

formed by granitization and local fusion of the host 

metamorphic rock.

The leucocratic rocks form an extraordinarily complex 

assemblage of dikes, sills, irregular clots, pods, and small 

stocks or plutons in the Swakane Biotite Gneiss and in 

the Seven-fingered Jack and older granitoid intrusives. 

The shape of individual masses is rather strongly dependent on the fabric of the host rock; thus, in foliated 

rocks, lenses and sills parallel to foliation are 

characteristic, whereas irregular dikes and masses form 

in more massive rocks. In many places, bodies of 

leucocratic material are numerous enough to form 

migmatites (fig. 37). In the Swakane, the amount of
PRE-TERTIARY INTRUSIVE ROCKS 29

FIGURE 33. Contact complex of the Entiat pluton, Lucerne 

quadrangle, showing gabbro chilled against quartz diorite.

leucocratic material increases from the southeast to the 

northwest. Inasmuch as the rocks are more deeply 

eroded to the northwest, it may be that the abundance of 

leucocratic rocks in the Swakane is at least partly depth 

dependent. The largest masses of leucocratic rock occur 

east of Pomas Creek in the Lucerne quadrangle. Most of 

the leucocratic quartz diorite and granodiorite is nearly 

white and massive (fig. 38) but in places it is obscurely 

gneissic because of parallelism of mica flakes, mostly 

biotite. Fine-grained and medium-grained rocks are 

most abundant, but pegmatitic varieties are common, 

and all textural varieties are intergradational within 

single masses. The leucocratic rocks consist mostly of 

oligoclase and quartz; the main accessory mineral is 

biotite. Potassium feldspar is almost absent, except 

locally, as in a few dikes on the east side of Rock Creek 

and in pods and pegmatitic masses on the south side of 

Chiwawa Mountain where microcline is sufficiently 

abundant for the rock to be classed as granodiorite. 

Minor accessory minerals are apatite, titanite, opaque 

minerals, and muscovite. Chlorite and epidote replace 

biotite, and sericite replaces oligoclase. Most of the 

oligoclase has a composition of about An2 o, but some is

122°45'

48° 

00'

SEVEN^ 

FINGERED

JACK 

PLUTONS

EXPLANATION

Biotite-hornblende-quartz diorite 

of Seven-fingered Jack plutons

Hornblende-biotite and biotitehornblende-quartz diorite

Hornblende diorite and gabbro

Biotite-ho rnblende-qua rtz

diorite 

Contact complexes and related

melanges

Contact 

Sample locality

;37

5 KILOMETERS

FIGURE 34. Map showing location of modally analyzed samples from 

the Seven-fingered Jack and Entiat plutons, Holden and Lucerne 

quadrangles.

as calcic as Anno. No discernible difference in texture or 

mode of occurrence was apparent between rocks containing medium oligoclase and those containing calcic 

oligoclase. Much of the oligoclase is anhedral or forms 

rounded grains, and is largely unzoned, but some thin 

sections have subhedral crystals of oligoclase that are oscillatorily zoned. Rounded blebs of quartz as inclusions 

are common in oligoclase. Quartz mostly occurs as irregular lenses and folia of interlocking grains that wrap 

around the larger plagioclase grains. Biotite occurs as 

orange-red shreds. Textures are xenomorphic and have 

crystalloblastic appearance generally, but some 

specimens approach a hypidiomorphic texture. 

Protoclasis is fairly common.
30 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 8. Modal analyses of samples of diorite, gabbro, quartz diorite, and quartz diorite gneiss from the Seven-fingered Jack and Entiat

plutons, central Washington

Sample

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

Plagioclase

54.4

53.6

46.3

32.0

58.4

51.8

51.0

53.6

50.1

54.7

54.7

42.2

59.0

52.7

50.7

50.2

49.5

39.2

56.7

57.6

49.1

57.2

55.6

49.8

44.0

58.7

43.3

51.9

53.3

56.0

50.8

47.6

65.2

45.1

43.2

41.2

58.5

45.0

43.6

42.0

48.1

Potassium 

feldspar

0

0

0

0

0

0

0

0

0

0

0

0.2

0

.5

0

0

.6

5.5

0

0

0

1.4

1.0

0

4.2

0

3.4

0

.7

3.5

0

.7

0

3.1

4.0

0

3.1

0

11.3

0

0

Quartz

19.4

17.8

13.6

14.5

16.5

11.6

21.9

19.1

8.9

11.2

11.7

15.9

10.2

7.5

5.8

31.2

22.9

28.7

21.9

18.7

26.5

14.9

20.3

1.9

19.0

9.2

19.9

.4

18.3

15.6

38.7

22.0

17.8

21.9

25.6

22.1

20.6

18.4

17.3

27.1

25.1

Biotite

2.8

10.6

7.9

2.5

0

.2

14.0

4.4

3.3

6.1

6.6

.3

3.5

0

.5

3.9

11.6

13.7

10.4

7.9

3.1

9.5

11.0

.4

20.3

.5

20.7

.6

19.2

11.4

3.3

20.7

5.7

15.2

12.5

18.3

11.7

25.5

9.4

12.8

.4

Hornblende

8.6

16.5

21.5

28.5

12.2

22.3

9.2

20.0

31.8

27.0

24.0

31.0

13.9

27.8

38.4

13.0

4.8

2.1

9.3

13.3

18.3

14.9

6.8

43.0

7.9

22.1

11.1

35.8

3.2

1.7

4.1

6.4

0

8.8

13.3

12.4

4.2

5.2

14.8

16.9

25.2

Accessory 

and secondary minerals

14.8

1.5

.7

22.5

12.9

14.1

3.9

2.9

5.9

1.0

3.0

10.4

13.4

11.5

4.6

1.7

10.6

12.8

1.7

2.5

3.0

5.5

5.3

4.9

4.6

9.5

1.6

11.3

5.3

11.8

3.1

2.6

11.3

5.9

1.4

6.0

1.9

5.9

3.6

1.2

1.2

Total 

mafic 

minerals

26.2

27.6

30.1

53.5

25.1

36.6

27.1

27.3

41.0

34.1

33.6

41.7

30.8

39.3

43.5

18.6

27.0

28.6

21.4

23.7

24.4

29.9

23.1

48.3

32.8

32.1

33.4

47.7

27.7

24.9

10.5

39

17

29.9

27.2

13.7

17.8

36.6

27.8

30.9

25.8

Anorthite in 

plagioclase crystals (percent)

Average

46

46

38

38

41

38

38

42

47

47

40

38

44

43

38

33

34

35

39

35

37

40

39

48

34

36

38

48

40

47

27

39

26

58

38

35

38

39

37

27

30

Core

51

49

43

41

44

44

40

47

0

0

48

50

0

0

55

37

36

39

47

0

42

45

45

64

0

43

41

0

44

0

0

42

38

60

0

0

0

41

47

40

0

Rim

33

33

31

15

38

31

35

38

0

0

33

34

0

0

28

31

27

27

35

0

33

33

31

32

0

31

14

0

19

0

0

36

11

55

0

0

0

35

31

18

0

Remarks

Hypidiomorphic .

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Hypidiomorphic-protoclastic.

Xenomorphic.

Protoclastic.

Do.

Hypidiomorphic .

Do.

Do.

Hypidiomorphic-cataclastic.

Do.

Hypidiomorphic.

Do.

Cataclastic.

Hypidiomorphic-protoclastic.

Hypidiomorphic .

Do.

Do.

Do.

Protoclastic.

Xenomorphic-cataclastic.

Hypidiomorphic .

Xenomorphic-cataclastic.

Do.

Do.

Hypidiomorphic; 6 percent

muscovite

Hypidiomorphic-cataclastic.

Protoclastic.

Do.

Do.

Hypidiomorphic . Do.

Do.

Xenomorphic.

Chemical and spectrographic analyses and norms of 

leucocratic quartz diorite and granodiorite are given in 

table 10, and a plot of the norms is shown in figure 36.

The origin of these enigmatic rocks is not altogether 

clear: some are obviously intrusive, disrupt the enclosing 

host rocks, and contain disoriented inclusions of them. 

Others, particularly the leucocratic rocks in the 

Swakane, seem mostly to have sweated out of the gneiss 

passively by a process of metamorphic segregation. In 

places, dikes of leucocratic quartz diorite or granodiorite 

cut masses of similar material that seem to be 

metamorphic segregations. Contacts of leucocratic rock 

with enclosing gneisses or intrusive rocks are commonly 

sharp, but in the gneissic rocks, particularly the 

Swakane, the adjacent gneiss in most places is enriched 

in mafic constituents as though the felsic constituents 

had migrated from the Swakane Biotite Gneiss. In other 

places, leucocratic material, apparently derived by

metamorphic segregation, became mobile and formed 

crosscutting dikes; a good example is illustrated by 

Crowder (1959, pi. 6, fig. 7). Available evidence suggests 

that although the leucocratic rocks vary little in composition or appearance, some formed by metamorphic 

segregation and others are probably felsic differentiates 

of intrusive rocks. Certainly in many places the two 

processes are so blurred that it seems they were essentially contemporaneous, but the abundance of these 

rocks in the Swakane everywhere and their localized occurrence in the Seven-fingered Jack and older plutons 

strongly suggests a wide difference in age for some of 

these rocks. Mattinson (1972, p. 3778-3779), for example, obtained ages that ranged from 60 to 90 m.y. for 

zircons from pegmatitic material collected from the 

Swakane along the Columbia River, from Misch's 

"Skagit" gneiss, and from a Dumbell Mountain pluton. 

These ages probably are from igneous-derived material.
PRE-TERTIARY INTRUSIVE ROCKS 31

TABLE 9. Chemical and spectrographic analyses and norms of rock 

samples from the Seven-fingered Jack and Entiat plutons, Holden 

and Lucerne quadrangles

[For samples 1 and 2 rapid rock analyses by P.L.D. Elmore, K. D. White, and S. D. Botts. For 

sample 3, SiOs and AUOs determined colorimetrically; Fe2C>3, MgO, CaO, and Mn determined by atomic absorption; FeO determined volumetrically; Na2d and KiO determined 

by flame photometer; analysts: Violet Merritt, H. H. Lipp, G. D. Shipley, and G. T. Burrow. 

Spectrographic analyses by K. E. Valentine and Harriet Neiman. Leaders (---), below sensitivity limit]

Sample--------------- 123

Chemical analyses (percent)

SiO2 ----------------- 57.5 61.8 51.5

A12O3 ----------------- 18.0 17.0 15.7

Fe2O3 ---------------- 2.7 2.1 7.80

FeO------------------ 3.9 3.5 5.9

MgO----------------- 3.6 2.4 6.6

CaO ----------------- 6.9 5.2 8.00

Na2O----------------- 3.8 3.8 3.14

K2O------------------ 1.0 1.7 .39

TiO2 ----------------- .98 .71 0

P2L/5 o ----------------- .oZ do .00 oci nU

MnO----------------- .12 .11 .14

H2Q.................. i.o 1.2 0

CO2 ------------------ .07 .05 0

Total------------- 100 100 99

Semiquantitative spectrographic analyses (parts per million)

Ba ------------------- 100 100 70

Co ------------------- 10 10 20

Cu ------------------- 10 10 30

Ga ------------------- 30 30 15

Ni ------------------- 50

Sc ------------------- 10 10 20

Sr ------------------- 300 300 300

V -------------------- 10 10 300

Y -------------------- 10 10 20

Yb------------------- 

Zr ------------------- 30 

113

100 50

	Norms

q ...--.....---......- n.61 18.07 5.33

or-------------------- 5.97 10.18 2.32

ab ------------------- 32.49 32.55 26.77

an ------------------- 29.44 23.69 27.83

di-------------------- 2.10 .00 9.73

hy ------------------- n.63 9.83 16.62

c--------------------- 0 .35 0

mt ------------------- 3.96 3.09 11.40

il ....--.....----..... 1.88 1.37 .00

ap ------------------- .76 .76 .00

cc -------------------- .16 .11 .00

Total------------- 100.00 100.00 100.00

Plagioclase composition

an ------------------- 47.5 42.1 51.0

TABLE 9. Chemical and spectrographic analyses and norms of rock 

samples from the Seven-fingered Jack and Entiat plutons, Holden 

and Lucerne quadrangles Continued

Sample descriptions

1. Composite sample of biotite-hornblende-quartz diorite.

2. Composite sample of hornblende-biotite-quartz diorite.

3. Hornblende gabbro of contact complex.

Quartz

Plagiociase

Potassium 

feldspar

EXPLANATION

 5 Biotite-hornblende-quartz diorite 

o'B Hornblende-biotite-3nd biotitehornblende-quartz diorite 

A32 Hornblende-quartz diorite gneiss

FIGURE 35. Plot of modes of rock samples from the Seven-fingered 

Jack and Entiat plutons, Holden and Lucerne quadrangles, on a 

quartz-potassium feldspar-plagioclase diagram. Sample analyses are 

given in table 8.

TENPEAK AND WHITE MOUNTAIN PLUTONS

The Tenpeak and White Mountain plutons consist of 

closely similar rocks and are probably connected at 

depth. From north of Glacier Peak volcano, near the 

center of the Glacier Peak quadrangle, the Tenpeak 

pluton extends south-southeast across the southwest corner of the Holden quadrangle and beyond. Along the 

southern border of the mapped area, the pluton has a 

width of about 8 km. The White Mountain pluton forms 

a thick sill-like mass extending from the south-central 

part of the Holden quadrangle southward roughly 8 km, 

about 3 km of which are south of the quadrangle. The 

width is about 4 km. South of the mapped area, both 

plutons have been studied and described by Van Diver
32 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Piagioclase

Potassium

feldspar

EXPLANATION

A' Leucocratic quartz diorite

and granodiorite 

2 Seven-fingered Jack and

Entiat plutons

FIGURE 36. Plot of norms of leucocratic quartz diorite and 

granodiorite samples and rock samples from the Seven-fingered Jack 

and Entiat plutons, Holden and Lucerne quadrangles. Sample 

analyses are given in tables 9 and 10.

(1967) as orthogneiss. He stated (p. 146) that, "It is not 

known whether the igneous parent rock of the White 

River Orthogneiss represents a premetamorphic intrusive later than the deposition of the supracrustal sequence, or whether it is part of the basement on which 

the sequence was laid down." He thought that the 

weight of evidence probably supported a "fault 

emplacement" of the pluton (p. 133), but that at any 

event, the plutons were metamorphosed concomitant 

with the enclosing gneisses. However, the plutons, which 

are about 90 m.y. old (Engels and others, 1976) contain 

fairly numerous inclusions of the host metamorphic 

rocks, and these rocks probably correlate with part of the 

upper Paleozoic metamorphic rocks of the Holden area. 

Van Diver apparently considered the protoclastic 

margins of the plutons to be recrystallized shears related 

to probable tectonic emplacement of the plutons.

The plutons consist of a variety of rocks ranging from 

granodiorite to gabbro and hornblendite, but by far the 

most abundant rock type is quartz diorite. The Tenpeak 

is the more complex of the two plutons and consists of a 

number of separately mapped units that differ

FIGURE 37. Migmatite of leucocratic quartz diorite in biotitehornblende-quartz diorite of the Seven-fingered Jack pluton, Holden 

quadrangle.

FIGURE 38. Leucocratic quartz diorite, Holden quadrangle.

somewhat in composition and appearance. The largest of 

these units, consisting of the same rock type that makes 

up most of the White Mountain pluton, is mostly lightcolored, medium-grained hornblende-biotite-quartz 

diorite. Also common to both plutons are spectacularappearing contact complexes consisting of an extraordinary variety of rocks. The second unit of the Tenpeak 

pluton is a layer nearly 1 km thick that borders the 

northeast side of the pluton. It consists of hornblendeand (or) biotite-quartz diorite flaser gneiss. Separating 

this unit from the main mass of the pluton, the lightcolored hornblende-biotite-quartz diorite, is a unit of in-
PRE-TERTIARY INTRUSIVE ROCKS 33

TABLE 10. Chemical and spectrographic analyses and norms of 

samples of leucocratic quartz diorite and granodiorite, central 

Washington

[For samples 1-3, SiO2 and A12(X determined by X-ray fluorescence; total Fe, MgO, and CaO 

determined by atomic absorption; FeO determined volumetrically; Na2O and KoO determined by flame photometer; TiO2 determined colorimetrically; analysts: J. S. Wahlberg, 

Wayne Mountjoy, and G. T. Burrow. For samples 4 and 5, rapk rock analyses by P.L.D. 

Elmore, K. E. White, and S. D. Bolts. Spectrographic analyses by Harry Bartron and Harriet Neiman. N.d., not determined; leaders (- - -), below limit of detection]

Sample----------- 12345

Chemical analyses (percent)

SiO2 ------------- 74.0 70.00 75.0 74.2 75.9

A12O3 ------- ------ 14.6 16.8 14.0 15.5 14.1

Fe2O3 ------------ .44 .64 .47 -48 .6

FpO 11^ 1 1 Q Sfi Wl Qfl

PaO 9 tio 'J IA Q nn 1 s 9 n

Na2O------------- 5.20 5.76 4.78 3.8 3.2

KzO-------------- .99 .58 .57 3.4 2.1

TiC-2 ------------- .09 .14 .10 .08 .16

P2O5 ------------- N.d. N.d. N.d. .04 .06

MnO ------------- N.d. N.d. N.d. .01 .03

HO -------------- N.d. N.d. N.d. .64 .96

C02 -------------- N.d. N.d. N.d. .05 .05

Total--------- 100 99 99 101 101

Semiquantitative spectrographic analyses (parts per million)

B ---------------- ... 10 10

Rfl cnn ^00 70O 3 OHO *} OOO

Be --------------- ... ... i i

Co --------------- 5

Pr 1^9 9ft

Cu--------------- 3 5 3 10 20

Mo--------------- 3 3

Ni -------------- ... ... ... 5 5

Pb --------------- 10 10 30 20

SC --------------- ... 3

Sr --------------- 1,000 1,500 1,000 400 700

V---------------- 30 30 20 20 40

Zr --------------- 70 70 50 40 30

Ga --------------- 15 15 15 10 10

Norms

n QQ 9O 9C 1f\ Q'? £!~1 Q A QQ A A H9

or---------------- 5.88 3.46 3.39 20.09 12.44

ab --------------- 44.20 49.24 40.68 32.13 27.13

an --------------- 12.91 16.75 14.98 8.35 9.24

hy --------------- 2.71 2.60 2.24 .89 2.55

r 97 PA 17 9^1 ^ 90

mt --------------- .64 .94 .68 .70 .87

U 1 7 97 1 Q 1 ^ *}0

ap --------------- 0 0 0 .09 .14

cc---------------- 0 0 0 .11 .11

Total --------- mono mono mono mono mono

TABLE 10. Chemical and spectrographic analyses and norms of 

samples of leucocratic quartz diorite and granodiorite, central 

Washington Continued

Sample--------- 12345

Plagioclase composition

an -------.-.... 22.6 25.4 26.9 20.6 25.4

Sample descriptions

1. Sample of irregular trondjhemite mass. 

2. Sample of trondjhemite dike. 

3. Sample of leucocratic, veinlike segregations in hornblende gneiss. 

4. Composite sample of leucocratic granodiorite pods in biotite gneiss. 

5. Composite sample of leucocratic granodiorite pegmatite dikes.

terlayered light- and dark biotite-hornblende diorite, 

quartz diorite, quartz diorite gneiss, and flaser gneiss. 

The unit is about half a kilometer thick. Confined to the 

northwestern end of the Tenpeak pluton, in the Glacier 

Peak quadrangle, is a third unit consisting of dark 

biotite-hornblende diorite.

HORNBLENDE-BIOTITE-QUARTZ DIORITE 

AND QUARTZ DIORITE GNEISS

The hornblende-biotite-quartz diorite and quartz 

diorite gneiss composing the bulk of both plutons is 

mostly a light-colored, medium- grained rock in which 

crystals of hornblende as much as 1 cm long and flakes of 

biotite are conspicuous (fig. 39). In the White Mountain 

pluton, small amounts of granodiorite indistinguishable 

in outcrop from quartz diorite also occur. Reddish -amber 

crystals of garnet nearly 1 cm across are locally common 

in the Tenpeak pluton, and rhombs of sphene as much as 

0.6 cm long are characteristic of both plutons. Much of 

the rock is slightly foliated, and most also has a distinct 

lineation defined by the parallel orientation of 

hornblende and scattered elongate xenoliths. In places, 

particularly near contacts, inclusions are plentiful; they 

range from angular, undigested fragments of host rocks 

to vague rounded schlieren that differ little from quartz 

diorite. Contacts of the granodiorite in the Tenpeak 

pluton with the interlayered zone unit are gradational, 

but elsewhere the quartz diorite becomes increasingly 

streaky near most contacts, particularly those that are 

more or less conformable, and here the rock is commonly 

highly gneissic.

FLASER GNEISS

The flaser gneiss borders the entire northeast side of 

the Tenpeak pluton. The rock is fine to medium grained

anrl r-nntainc TwrrVh\rrr»r»ln«t e r\f er»Hir> nnrtaeino pnvplrmpH
34 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

-}

FIGURE 39. Homblende-biotite-quartz diorite from the Tenpeak 

pluton, Holden quadrangle.

by warped folia of biotite. Locally, hornblende crystals 

and mafic streaks define a lineation. Coarse crystals of 

sphene are common, but garnet is rare. The contacts of 

this unit with metamorphic rocks to the northeast are 

almost strictly conformable and range from sharp to 

gradational, but where gradational, the gradational zone 

is fairly narrow and consists in part of lit-par-lit injections. The southwest contact with the interlayered zone 

unit is gradational.

INTERLAYERED ZONE UNIT

The interlayered zone unit consists mostly of alternating lenses and layers of light- and dark-colored 

biotite-hornblende diorite and quartz diorite gneiss, and 

flaser gneiss (fig. 40). Even the lighter colored lenses and

FIGURE 40. Interlayered biotite-hornblende-quartz diorite gneiss and 

hornblende schist of the interlayered unit of the Tenpeak pluton, 

Holden quadrangle.

layers of light-colored gneiss, however, are generally 

darker than the rocks that form the interior of the 

pluton. The lenses and layers of gneiss and flaser gneiss 

range in thickness from a few centimeters to many 

meters; mixed with these are thinner sheets and thin 

wisps of hornblende schist, quartzite, and rare hornblendite. Schist inclusions are locally spotted with 

porphyroblasts of plagioclase. Gneisses are fine to 

medium grained and contain augen of plagioclase surrounded by anastomosing mats of finer grained 

hornblende. Contacts between layers and lenses or different rock types may be either sharp or gradational.

CONTACT COMPLEXES

Contact complexes of the White Mountain pluton are 

very largely confined to the northwest end where it 

trangresses the enclosing metamorphic rocks; those of 

the Tenpeak pluton are confined to the southwest side. 

These complexes are identical, in most respects, to those 

associated with other pre-Tertiary intrusive masses in 

the mapped area and consist of spectacular melanges of 

gabbro, diorite, hornblendite, quartz diorite, pegmatitic 

diorite, and inclusions of metamorphic rocks. Crystals in 

some of the hornblendite and pegmatitic rocks are as 

much as 5 cm long. The main body of quartz diorite 

sharply cuts the contact complex in some places, but 

elsewhere the contact has a stirred appearance that 

strongly suggests that the complex was plastic or molten 

when the quartz diorite was intruded. Locally, drawnout, highly irregular masses of the complex are enclosed 

in quartz diorite.

PETROGRAPHY

Under the microscope, rocks of the various units are 

seen to be rather similar in composition, the principal 

difference between the light and dark colored quartz 

diorites being in the abundance of biotite and 

hornblende. Uncontaminated rocks consist of 45 to 55 

percent sodic andesine, 11 to 25 percent quartz, 8 to 15 

percent biotite, and 0 to 25 percent hornblende as 

primary minerals, and muscovite, apatite, opaque 

minerals, potassium feldspar, and as much as 2 percent 

titanite as accessory minerals. Granodiorites, however, 

contain as much as 15 percent potassium feldspar, 

mostly microcline. Primary, coarse-grained, euhedral 

clinozoisite-epidote is notably abundant and occurs in 

amounts of as much as 7.5 percent.

Plagioclase ranges in composition from Ani8 on the 

rims of some crystals to An53 in the most calcic cores; the 

average composition of plagioclase in most thin sections 

is about Anas. Oscillatory and patchy zoning is fairly 

common, but twinning has destroyed zoning in many 

crystals. Adjacent twin lamellae can differ in composition by as much as 3 or 4 percent of anorthite.
PRE-TERTIARY INTRUSIVE ROCKS 35

Myrmekite is common along granulated zones and adjacent to potassium feldspar. Hornblende is pleochroic in 

various shades of green, and much of it contains inclusions of quartz and less commonly of plagioclase. 

Probably some of the quartz grains are replacements 

rather than inclusions. Hornblende has also been extensively replaced by biotite, in many places, with a separation of fine-grained titanite. Quartz occurs as replacements of earlier formed minerals and as irregular seams 

of interlocking grains; lines of liquid inclusions are 

notably abundant. Much of the coarse-grained, euhedral 

clinozoisite-epidote contains blebs of simultaneously extinguishing quartz in intergrowths identical in appearance to myrmekite (fig. 41). This clinozoisiteFIGURE 41. Intergrowth of clinozoisite-epidote and quartz resembling 

myrmekite, quartz diorite from the Tenpeak pluton, Holden 

quadrangle, cl, clinozoisite-epidote; pi, plagioclase; q, quartz.

epidote, in fact, appears to be a primary mineral growing 

in equilibrium with plagioclase and hornblende. Some 

scattered grains of clinozoisite-epidote have cores of allanite. Primary epidote in the Ellicott City Granodiorite, 

Maryland, has been described by Hopson (1964). 

Dietrich (1961, p. 42-45) indicated that high pressure 

and (or) high content of hydroxyl in magma favors 

development of primary epidote. Small amounts of 

chlorite replace biotite, and sericite sparingly replaces 

plagioclase, commonly as flakes along cleavage planes. 

Garnet and calcite occur in small amounts in a few 

sections.

The textures of the quartz diorite range from 

hypidiomorphic to xenomorphic with barely perceptible 

to extensive protoclastic modifications. Rocks of the 

main body of the two plutons are mostly hypidiomorphic 

and show only minor protoclasis, whereas rocks of the interlayered and particularly the flaser-gneiss units are 

highly protoclastic, and it is protoclasis that lends the 

gneissic appearance to so much of the rocks.

Modal analyses of Tenpeak and White Mountain 

rocks are shown in table 11, and chemical and 

spectrographic analyses and norms in table 12. Locations of modally analyzed specimens are shown in figure 

42, the modes are plotted in figure 43, and the norms are 

shown in figure 44. A plot of the major oxides is shown in 

the variation diagram (fig. 13).

SULPHUR MOUNTAIN PLUTON

Only a small, poorly exposed lobe of the Sulphur 

Mountain pluton extends into the western edge of the

TABLE 11. Modal analyses of samples of quartz diorite gneiss from the Tenpeak and White Mountain plutons, Holden quadrangle

Sample 

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Plagioclase

53.0

36.9

51.0

54.7

48.1

51.0

44.7

42.9

38.1

48.5

32.8

52.1

44.6

49.3

44.8

Potassium 

feldspar

0

0.6

0

0

.2

.1

4.7

0

.2

.4

0

0

0

15.8

.8

Quartz

25.3

36.0

21.0

22.5

19.4

16.4

24.4

20.8

18.5

14.4

5.2

17.8

11.6

25.3

22.8

Biotite

12.4

11.1

11.1

11.6

12.3

.8

14.4

14.0

15.7

14.4

4.7

15.2

15.4

6.7

12.8

Hornblende

3.4

0

14.2

7.6

15.7

22.2

3.7

12.4

18.9

14.6

50.7

0

18.8

0

7.7

Accessory 

and secondary minerals

5.9

15.4

2.7

3.6

4.3

9.5

8.1

9.9

8.6

7.7

6.6

14.9

9.6

2.9

11.1

Total 

mafic 

minerals

21.7

26.5

28.0

22.8

32.3

32.5

26.2

36.3

43.2

36.7

62.0

30.1

43.8

9.6

31.6

Anorthite in 

plagioclase crystals (percent)

Average

31

26

32

34

34

38

26

31

33

30

51

32

33

27

35

Core

41

34

37

50

42

45

34

40

52

50

55

0

41

31

42

Rim

22

17

20

26

33

30

18

28

17

23

43

0

23

8

19

Remarks

Protoclastic.

8.5 percent muscovite;

protoclastic.

Hypidiomorphic.

Do.

Protoclastic.

Hypidiomorphic .

Do.

Do.

Do.

Coarse, euhedral epidote;

hypidiomorphic.

Quartz gabbro of

contact complex;

hypidiomorphic.

Protocluetic.

Subparallel andesine

laths; hypidiomorphic.

Protoclastic.

Hypidiomorphic.
36 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 12. Chemical and spectrographic analyses and norms of 

composite rock samples from the Tenpeak and White Mountain 

plutons, Holden quadrangle

[Standard rock analyses by Dorothy F. Powers. Spectrographic analyses by P. R. Barnett]

--------.--.. i 2

Chemical analyses (percent)

SiO2 ---------

Fe2O3 --------

FpO -

MgO ---------

PaO

Na2O---------

if r\

TT r\ i

H f)

rr|;p\

ID f\

MnO---------

PO

Total-----

CO QC\

1C GO

1 Qfl

Q Qfl

O QC

--------.-__. K no

O HE.

1 QQ

.............. .74

------ 08

.............. .74

00

-.-......-... .11

nn

.---_--.-..- 99 61

Semiquantitative spectrographic analyses (parts

Ba- ------ -

Co -----------

Cr -----------

Cu -----------

fla

Ni -----------

Sr -----------

V ------------

Y ------------

Yb ------

Zr -----------

7OO

............. 7

1C.

............. 15

............. 7

IF;

............. 1,500

ICf)

1C

1 p>

icn

59.67 

16.34 

1.48 

4.78 

3.61 

6.11 

3.43 

1.67 

1.14

.92 

.13

99.65

per million)

700 

15 

70 

15 

15 

15 

15 

700 

150 

15 

1.5 

150

Norms

q ............

ah

di------ 

hy -- - ..

il ............

Total -----

1C OO

8 Q1

QO in

OK Aft

2

OC

9

7fi

1 Q1

1 49

no

inn nn

13.95 

10.02 

29.46 

24.65 

3.45 

13.82 

2.18 

1.77

.05

100.00

Plagioclase composition

A A O 45.5

Sample descriptions

1. Composite sample of biotite-hornblende-quartz diorite (Tenpeak).

2. Composite sample of hornblende-biotite-quartz diorite (White 

Mountain) .

121°00'

EXPLANATION

Dark-colored biotite-hornblende 

diorite and quartz diorite

Hornblende-biotite-quartz diorite 

and quartz diorite gneiss

Hornblende-and (or) biotite-quartz 

diorite flaser gneiss

Interlayered light- and dark-colored 

diorite and quartz diorite gneiss

Contact complex

 Contact

 ^ Sample locality

FIGURE 42. Map showing location of modally analyzed samples from 

the Tenpeak and White Mountain plutons, Holden quadrangle.

Quartz

Plagioclase

Potassium 

feldspar

FIGURE 43. Plot of modes of quartz diorite and quarts diorite gneiss 

samples from the Tenpeak and White Mountain plutons, Holden 

quadrangle, on a quartz-potassium feldspar-plagioclase diagram. 

Sample analyses are given in table 11.
PRE-TERTIARY INTRUSIVE ROCKS 37

Granodiorite of High 

r Pass pluton

Quartz diorite of Cardinal 

Peak pluton

Quartz diorite of 

Tenpeak pluton

'Quartz diorite of White 

Mountain pluton

Plagioclase 35

Potassium 

feldspar

FIGURE 44. Plot of norms of rock samples from the Tenpeak, White 

Mountain, Cardinal Peak, and High Pass plutons, Holden 

quadrangle, on a quartz-potassium feldspar-plagioclase diagram. 

Sample analyses are given in table 11.

Holden quadrangle, but the pluton underlies a considerable area in the northern part of the adjacent 

Glacier Peak quadrangle. In the Holden quadrangle, the 

pluton consists of light- to medium-gray, mediumgrained hornblende-biotite granodiorite and granodiorite 

gneiss (fig. 45). Much of it forms augen gneiss containing 

conspicuous eyes of quartz. Only a few isolated outcrops 

of the rock are nongneissic. Contacts with host rocks are 

variable, sharp in some places, gradational across a few 

meters in others, and in still others consisting of lit-parlit zones of granodiorite and schist or gneiss. The contact 

with the younger High Pass pluton is particularly irregular, for numerous dikes and irregular masses of the 

High Pass extend varying distances into the Sulphur 

Mountain. Inclusions of schist and gneiss are generally 

common near contacts with the metamorphic host rocks. 

The granodiorite at Sulphur Mountain consists of 

oligoclase, quartz, microcline, and biotite as major constituents; most of the rock also contains a few percent of 

hornblende, but it is absent locally. Crowder, Tabor, and 

Ford (1966) reported that considerable clinopyroxene occurs in the pluton in the Glacier Peak quadrangle. 

Sphene occurs in quantities greater than 1 percent, and 

coarse-grained, euhedral clinozoisite similar to that in 

the Tenpeak pluton is a common accessory; apatite is 

rare. Secondary minerals are chlorite, sericite, and finegrained epidote. Both oscillatory and patchy zoning are 

common in the oligoclase. Textures range from 

xenomorphic to hypidiomorphic, and all show conFIGURE 45. Gneissic granodiorite from the Sulphur Mountain pluton, 

Holden quadrangle.

siderable protoclasis; the augen gneiss, in particular, 

shows intense protoclasis.

The age of the granodiorite at Sulphur Mountain 

relative to the Tenpeak-White Mountain rocks on a 

geologic basis is not known, but Engels (Engels and 

others, 1976) obtained a potassium argon Late Cretaceous age of about 70 m.y. for hornblende (table 38) from 

the Sulphur Mountain.

Modal analyses of the pluton are shown in table 13 and 

figure 46.

HIGH PASS AND BUCK CREEK PLUTONS

The closely related High Pass and Buck Creek 

plutons, unlike most of the larger intrusive masses in the 

region, are decidedly tabular, and the Buck Creek, in 

particular, is sill-like. Both masses are in the westcentral part of the Holden quadrangle and together underlie an area of about 20 km2 . The rocks vary considerably in appearance from place to place because of 

grain size and degree of foliation, but the composition is 

fairly uniform, except locally near contacts where considerable reaction with host rocks has occurred. The 

High Pass pluton consists of light-colored, mediumgrained biotite granodiorite and quartz diorite (fig. 47); 

the western part of the mass is mostly massive, but the 

eastern part has a distinct foliation resulting from 

protoclasis and is accentuated by a parallelism of biotite 

flakes (fig. 48) . In the thick part of the mass, east of High 

Pass, the rock becomes progressively coarser grained and 

better foliated upward or from north to south in the 

mass. Foliation is most striking near the south contact of 

the pluton 1.6 km west of Buck Mountain. Here the rock 

is gneissic, and biotite aggregates form thin undulatory 

discontinuous folia that separate irregular layers of 

protoclastically deformed quartz and feldspar 1 to 3 mm 

thick. Much of the Buck Creek pluton is covered by
38 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE13. Modal analyses of samples of hornblende-biotite granodiorite from the Sulphur Mountain pluton, Holden quadrangle

Sample

No.

1

2

3

4

5

6

7

Plagioclase

43.0

45.8

52.1

49.2

51.6

42.6

44.3

Potassium

feldspar

7.6

9.8

13.8

7.6

10.3

9.5

10.6

Quartz

38.3

24.4

18.7

21.8

18.9

24.7

31.4

Biotite

8.6

15.9

11.4

13.4

14.2

13.7

10.9

Hornblende

0.5

.3

.1

3.1

0

.1

0

Accessory

and secondary minerals

2.0

4.8

3.9

4.9

5.0

9.4

2.8

Total

mafic

minerals

11.1

21.0

15.4

21.4

19.2

23.2

13.7

Anorthite in

plagiocls

Average

26

27

25

29

23

21

21

ise crystals (percent)

Core

32

32

30

44

27

25

24

Rim

24

18

17

23

17

16

19

Remarks

Porphyroclastic .

Cataclastic.

Protoclastic.

Porphyroclastic .

Protoclastic.

Do.

Xenomorphic.

Quartz

Pfagioclase

Potassium 

feldspar

FIGURE 46. Plot of modes of hornblende-biotite granodiorite samples 

from the Sulphur Mountain pluton, Holden quadrangle, on a quartzpotassium feldspar-plagioclase diagram. Sample analyses are given 

in table 13.

glacial debris, and the mass exposed on Helmet Butte 

possibly is not connected with the mass northeast of 

King Lake, but the rocks in both localities are identical 

and are indistinguishable from the foliated granodiorite 

and quartz diorite of the High Pass pluton.

The relation of the High Pass and the Buck Creek 

plutons to their host rocks differs considerably. The silllike Buck Creek pluton is emplaced along a zone of dislocation that, in part, followed the contact between the 

Swakane Biotite Gneiss and the much younger 

metamorphic rocks of the Napeequa River area. The 

High Pass pluton, on the other hand, is much more complex, being partly concordant and partly discordant. The 

narrow, southeastern part of the intrusive, in the valley 

of Alpine Creek, occupies the crest of a complex antiform 

(fig. 49). Northwestward, the pluton is a thick, southdipping sheet that both cut out and wedged apart the

FIGURE 47. Granodiorite from the High Pass pluton, Holden 

quadrangle.

metasediments and squeezed and distorted the large 

synform on Chiwawa Ridge.

The contacts of the plutons are mostly marked by litpar-lit zones, but locally contacts are uncomplicated and 

sharp (fig. 50), as are the contacts between layers in the 

lit-par-lit zones. Gradational contacts more than a few 

centimeters thick were not observed; on the other hand, 

considerable pegmatite occurs in the intrusive layers of 

the lit-par-lit zones. In most places, the lit-par-lit zones 

are only a few meters to a few tens of meters thick, but 

the upper contact, south of High Pass, is exceedingly 

complex and hundreds of meters thick. Here, thick dikes 

and sills of granodiorite intrude the gneisses, and large 

sheets of gneiss are entrapped in the granodiorite. The 

contact between the High Pass pluton and the older 

Sulphur Mountain pluton on Triad Creek is also highly 

complex; numerous dikes and irregular masses of High 

Pass rocks cut the Sulphur Mountain and extend varying distances into it. Locally inclusions of gneiss and 

schist are fairly common, especially near contacts.
PRE-TERTIARY INTRUSIVE ROCKS 39

FIGURE 48. Foliated granodiorite from the High Pass pluton, Holden 

quadrangle. A, Oriented across foliation; B, oriented parallel to 

foliation.

The High Pass and Buck Creek plutons consist of 

oligoclase, quartz, biotite, and potassium feldspar as 

primary minerals, and opaque minerals, apatite, zircon, 

and considerable titanite as accessory minerals. 

Clinozoisite-epidote and sericite are invariably present 

and chlorite occurs in most thin sections; less common 

are veinlets of prehnite and calcite. Hornblende and garnet occur locally near the contacts, apparently as unresorbed relicts derived from partly assimilated gneiss. 

Fractures in the granodiorite 1.6 km southwest of High 

Pass contain films of pink stilbite. Oligoclase, mostly as 

grains 1 to 3 mm across and ranging in composition 

between An2 2 and An2e, makes up 50 to 58 percent of the 

normal rock. Some crystals show oscillatory zoning 

within narrow compositional ranges, and patchy zoning 

is common. Myrmekitic intergrowths are also plentiful 

and are most abundant adjacent to potassium feldspar. 

The myrmekite crystallized later than potassium feldFIGURE 49. Granodiorite of the High Pass pluton, Holden quadrangle, in the core of an antiform in upper Paleozoic metasedimentary rocks. Note many sills and dikes of leucocratic quartz diorite in 

the metasediments.

spar and locally replaces it. Quartz in amounts ranging 

from 22 to 30 percent occurs as interstitial grains and as 

interlocking mosaics of grains forming irregular lenticular patches. Curved lines of inclusions, most of which 

appear to be liquid, are characteristic features of quartz. 

Biotite makes up 4 to 10 percent of the rock and occurs 

mostly as irregular shreds, many of which are bent. In 

some thin sections, biotite is most common along and 

oriented parallel to minute zones of granulation; it is 

pleochroic in shades of yellow and cinnamon brown. 

Microcline and lesser quantities of orthoclase occur in 

combined amounts of 5 to 13 percent and irregularly 

replace oligoclase, quartz, and biotite, fill fractures, or 

replace microscopic zones of granulation. Some 

microcline is perthitic, the exsolved plagioclase being 

almost pure albite. Albite of identical composition also 

forms clear, thin rims locally on scattered oligoclase 

crystals, and it seems entirely possible that all the albite
40 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

FIGURE 50. Contact of granodiorite of the High Pass pluton, Holden 

quadrangle, and hornblende schist. Note thin branching sills.

was derived by exsolution from microcline. Of the accessory minerals, only titanite occurs in any quantity or in 

other than minute grains; much of the titanite forms 

rhombs as much as 2 mm long.

Clinozoisite-epidote is the most plentiful of secondary 

minerals and makes up 1 to 5 percent of the rock. 

Crystals are mostly euhedral, as much as 2 mm long, and 

replace both oligoclase and biotite. The habit of the 

mineral is suggestive of a primary rather than a secondary origin; some of it is zoned around cores of allanite. Chlorite sparingly replaces biotite, and sericite

replaces oligoclase. Garnet and hornblende are confined 

to contact zones and are clearly relicts left from partly 

assimilated gneiss.

Textures of the granodiorite and quartz diorite of the 

High Pass pluton vary considerably from place to place, 

depending largely on the degree of protoclasis. The nonfoliated rock is typically hypidiomorphic, whereas the 

highly foliated rock is severely granulated and 

protoclastic; all gradations between the two extremes exist. The Buck Creek mass is less variable because of 

widespread protoclasis.

Modal analyses of the two plutons are given in table 

14, and chemical and spectrographic analyses and norms 

are given in table 15. Locations of modally analyzed 

specimens are shown in figure 51, and the modes are 

plotted in figure 52. The norms are plotted in figure 44, 

and the major oxides are plotted on the variation 

diagram of figure 13.

RIDDLE PEAKS PLUTON

The Riddle Peaks pluton was not investigated in the 

detail that would have been desirable for such an interesting mass of layered gabbro, and undoubtedly many 

features bearing on its emplacement and crystallization 

were either overlooked or not seen. Within the mapped 

area, the pluton is about 3.2 km wide and 6.5 km long, 

and it extends an unknown distance to the north. The 

original size of the pluton probably was considerably 

larger, for it is cut on all sides within the mapped area by 

later intrusions. Large blocks of the hornblende gabbro 

derived from the pluton occur as inclusions in the Cardinal Peak pluton south of Railroad Creek. Rocks of 

mineralogic composition and appearance identical to

TABLE 14. Modal analyses of samples of biotite-quartz diorite and granodiorite from the High Pass pluton, central Washington

Sample

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

Plagioclase

54.5

31.6

57.5

38.5

55.8

57.0

36.5

50.6

53.0

52.8

51.1

50.5

51.7

52.3

52.7

50.1

42.5

Potassium 

feldspar

2.7

26.3

9.5

21.4

4.9

7.7

25.2

9.7

9.2

3.3

7.6

2.0

8.2

12.4

11.6

9.6

10.8

Quartz

29.9

34.1

24.5

31.6

28.4

26.4

29.4

26.5

27.5

29.8

29.1

33.3

27.0

26.9

22.9

24.3

31.4

Biotite

10.6

6.3

5.8

8.3

6.7

6.4

8.3

11.2

7.5

9.9

5.9

11.5

6.5

1.3

7.1

8.9

10.7

Hornblende

0

0

0

0

0

0

0

0

0

0

0

0

0

0

3.4

5.1

.2

Accessory 

and secondary minerals

2.3

1.7

2.7

.1

4.2

2.5

.6

2.0

2.8

4.2

6.3

2.7

6.6

7.1

2.3

2.0

4.4

Total 

mafic 

minerals

12.9

8.0

8.5

8.5

10.9

8.9

8.9

13.2

10.3

14.1

12.2

14.2

13.1

8.4

12.8

16.0

15.3

Anorthite in 

plagioclase crystals (percent)

Average

24

22

20

20

22

25

27

23

24

24

26

26

27

23

26

29

27

Core

27

27

24

27

31

28

33

25

27

27

34

34

29

25

29

31

38

Rim

7

16

11

20

13

19

14

3

21

11

20

18

21

12

20

21

23

Remarks

Xenomorphic.

Protoclastic.

Do.

Hypidiomorphic.

Protoclastic.

Do.

Hypidiomorphic.

Do.

Protoclastic.

Do.

Do.

Do.

Do.

Do.

Hypidiomorphic .

Protoclastic.

Xenomorphic.
PRE-TERTIARY INTRUSIVE ROCKS 41

TABLE 15. Chemical and spectrographic analyses and norms of a 

composite sample of biotite-quartz diorite from the High Pass 

pluton, central Washington

[Standard rock analysis of composite sample by D. F. Powers; spectrographic analyses by P. R.

Barnett]

Chemical analysis 

(percent)

SiO2 ---------

Fe2O3 --------

T~/"I

MgO ---------

CaO

NazO ------

K

r\

H f\-L.

H

f\

Tin

P2 05 ---------

MnO ---------

COz----------

Total-------

- 70.43 

- 16.07 

- .36

1 £.1

- 3 24

- 1.77

- .42 

- .05

00

OQ

no.

- .01

QQ fi°.

ant

Ba 

Be 

Co 

Cr 

Cu 

Ga 

Ni 

Sr 

V -

Zr

Semiquantitative 

spectrographic 

lysis (parts per million)

1 £.00

--------- 1.5

0

--------- 1.5

0,

1C

......... 1,500

..---...- 15

1 ^0

Norms

q -----

ah

hy ---

il -----

Total

Plagiocl

98 99

in nn

on oo

.--..--.15.55

3 CO

00

CO,

CO

-.-..... .21

09

1 00 00

ase composition

OQ 1

1Z1°00'

48° 

04'

120°51'

-Buck Creek 

pluton

0 4 KILOMETERS

FIGURE 51. Map showing locations of modally analyzed samples of 

biotite-quartz diorite and granodiorite from the High Pass and Buck 

Creek plutons, Holden quadrangle. Sample analyses are given in 

table 14.

unlayered parts of the pluton crop out in contact complexes surrounding the Seven-fingered Jack and Entiat 

quartz diorite plutons and, conceivably, there may be 

some tie between these plutons and the Riddle Peaks 

pluton.

Rocks forming the pluton range from nearly black, 

medium- to coarse-grained hornblendites to white, 

hornblende-bearing, medium-coarse-grained anorthosites. Much of the rock is conspicuously layered (fig. 53), 

but the lower part of the mass between Ninemile and

Quartz

Plagiociase

Potassium 

feldspar

FIGURE 52. Plot of modes of biotite-quartz diorite and granodiorite 

samples from the High Pass pluton, Holden quadrangle, on a quartzpotassium feldspar-plagioclase diagram. Sample analyses are given 

in table 14.

FIGURE 53. Layered hornblende gabbro of the Riddle Peaks pluton 

and septum of gneiss in Riddle Peaks, Lucerne quadrangle. Septum 

of gneiss is about 80 m thick.
42 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Tenmile Creeks is only vaguely layered or consists of 

nearly structureless, massive, mesocratic hornblende 

gabbro (fig. 54). Weathered surfaces of the gabbro have a 

rasp-like texture because the calcic plagioclase has dissolved more rapidly than hornblende, and the 

hornblende crystals stand out in relief as sharp angular 

projections.

The contact between the relatively massive, only 

vaguely layered hornblende gabbro and the overlying, 

conspicuously layered hornblende gabbro is gradational 

in most places where it was seen; the layering becomes 

increasingly evident through the distance of a number of 

meters, but in one or two traverses across the contact the 

transition is abrupt, and the lowermost layers of the 

layer unit are as conspicuous as those above. Within the 

layered rock, zones of nearly massive, only vaguely 

layered gabbro many tens of meters thick alternate with 

zones of rhythmically layered rocks of similar thickness; 

thus, there is both a large-scale and a small-scale layering, for the individual rhythmic layers rarely attain a 

thickness of 30 cm. The large-scale layering can be seen 

particularly well in the high parts of Riddle Peaks 

(fig. 53).

Individual layers are remarkably straight, uniform in 

thickness, and continuous; many only a few centimeters 

thick may be traced for several hundred meters, 

although local contortions do occur (fig. 55). Other than 

gravity-stratified layers that resemble graded beds in 

sedimentary rocks and may be similarly used to determine tops of layers, no other pseudosedimentary structures were seen, such as crossbedding, trough layering, 

or unconformities as have been described in other 

layered intrusions (Wagner and Deer, 1939; Bateman, 

1965; Shawe and Parker, 1967; Irvine, 1967).

Layers consist of alternating hornblende-rich and 

hornblende-poor rocks (fig. 56). Hornblende-rich layers 

range from those only slightly enriched in hornblende to 

those of almost pure hornblendite. Such hornblendite

FIGURE 54. Hornblende gabbro from the Riddle Peaks pluton, 

Holden and Lucerne quadrangles.

FIGURE 55. Contorted layers in gabbro of the Riddle Peaks pluton, 

Holden and Lucerne quadrangles. Note nearly pure hornblendite 

layer bordered on each side by a thin layer of anorthosite Scale is 18 

cm long.

FIGURE 56. Layered gabbro from the Riddle Peaks pluton, Holden 

and Lucerne quadrangles.

layers are rarely more than 10 cm thick, but a few are as 

thick as 25 cm. The hornblende-poor or felsic layers, on 

the other hand, nowhere attain the same degree of 

segregation that occurs in the hornblende-rich layers and 

rarely contain less than 10 percent hornblende. Contacts 

between layers may be either gradational or sharp, but 

where sharp the crystals interlock across boundaries. In
PRE-TERTIARY INTRUSIVE ROCKS 43

general, lower contacts of hornblende-rich layers are 

sharp, whereas their upper contacts are gradational. In 

some localities, the grain size in layers also decreases 

upward.

A few layers were seen that are distinguished by grain 

size variations rather than composition; that is, 

relatively fine grained layers alternate with typical 

medium-grained ones. The fine-grained layers were not 

marked by any readily discernible variations in mineral 

proportions, and contacts with layers of normal grain 

size are generally gradational through the space of a fraction of a centimeter or more. Fine-grained layers are 

rarely more than 15 cm thick. In contrast to these finegrained layers, some pegmatitic gabbro containing 

hornblende crystals as much as 2 cm wide and 8 cm long 

was seen in talus blocks, but none was seen in place, and 

the relation of this pegmatitic material to more normal 

types of gabbro is unknown.

Planar lamination (Jackson, 1961, and 1967, p. 22) 

resulting from arrangement of platy crystals with their 

long dimensions in the plane of layering is almost universal in the hornblende gabbro and imparts a somewhat 

gneissic appearance to the rock, whether layered or not. 

Because of the bladed nature of hornblende, the lamination is more prominent in the more hornblende rich 

varieties than in the anorthositic varieties. In the plane 

of lamination, however, the orientation of the crystals is 

random, and no tendency to lineation was observed.

Inclusions, some of them hundreds of meters across, 

are scattered throughout both the layered and unlayered 

gabbro (fig. 53). In the upper part of the pluton from the 

Edil mine northward, screens or great sheets of host-rock 

gneisses are interlayered with the gabbro. In all 

probability, the huge inclusions are but disrupted remnants of screens formed earlier in the intrusive process. 

The larger inclusions and screens or septa of 

metamorphic rocks weather red because of their 

relatively high content of iron sulfide and, hence, are 

readily visible from a distance. Intermixed with the interlayered gabbro and screens of gneiss is a bewildering 

mixture of probable hybrid rocks derived from the interaction and partial fusion by gabbro of various types of 

metamorphic host rocks that range in composition from 

marble and quartzite to hornblende schists. Rocks that 

are not obviously partly assimilated metamorphic 

species are mostly quartz diorite of various compositions, but some are hornblende-quartz gabbros that differ from the normal hornblende gabbros only in containing sodic labradorite instead of medium bytownite plus 

considerable quartz. Conceivably, some of the rocks, especially perhaps some of the irregular masses of very 

coarse grained, somewhat pegmatitic hornblende-quartz 

gabbro, may be differentiates of the normal gabbro. This 

complex zone of screens, gabbro, and mixed rocks is 

further complicated by upper Eocene dikes and irregular

small intrusions that range in composition from quartz 

diorite to quartz monzonite. In fact, from the Edil mine 

both uphill and to the east, nearly every outcrop is of a 

different rock type.

Where intruded by the gabbro, many of the large inclusions split out along planes of foliation and, consequently, are either slab by or lenslike. Many of these 

slabby inclusions have attitudes that are parallel to the 

layering of the gabbro, but others, including most of the 

more blocky inclusions, lie at angles to the layering, and 

hence there is no parallelism between the foliation of the 

inclusions and the planar structures in the gabbro. Of 

the inclusions that were examined, none seemed to disturb the nearest laminae or layers of the gabbro, but 

nowhere was either lamination or layering seen to 

directly contact inclusions. Reasons for this relationship 

are not clear, but the lack of contact may be related to 

the contact phenomena associated with the inclusions. 

Contacts that are parallel to foliation of the inclusions 

are fairly sharp, although a coarsening of the grain size of 

the gabbro adjacent to the inclusions is pronounced, and 

layering and lamination fade. Where gabbro truncates 

foliation of the inclusions, on the other hand, the inclusion frays out into the gabbro; the contact is gradational 

through a considerable distance, the grain size of the 

gabbro is considerably coarser, and lamination and 

layering are nonexistent. In other words, where the gabbro magma had the opportunity to insinuate along 

rather than cut across foliation of all metamorphic rocks 

except marble, progressive assimilation of the inclusion 

by the magma was greatly enhanced and contacts are 

broadly gradational. Marble seems to be completely unaffected by the gabbro, and contacts with it are sharp.

In thin section the normal gabbro, whether layered or 

unlayered and where seemingly uncontaminated with 

digested host rocks, consists of varying proportions of 

bytownite and hornblende and lesser but still considerable quantities of magnetite. Titanite, apatite, interstitial pyrite, and rarely a little biotite are accessory. 

Although most of the rock is fresh, chlorite mostly 

ripidolite replaces some of the hornblende and some of 

the bytownite is either slightly sauseritized or sprinkled 

with small amounts of sericite. In some thin sections, 

scattered seams of epidote, prehnite, and rarely 

orthoclase cut the rock. Plagioclase varies in composition 

somewhat from place to place, ranging from about An?5 

to An,52, but most of it is in the bytownite range. The 

composition seems to be unrelated to vertical position 

within the mass. The plagioclase in some rocks that in 

hand specimen seem identical to normal gabbro may be 

as sodic as Ans2 , but rocks containing such plagioclase 

are associated with partly assimilated inclusions and are 

probably contaminated. Scattered crystals in nearly 

every thin section show a few rather faint oscillatory 

zones, and patchy zoning is fairly common. Thin rims of
44 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

progressively zoned labradorite surround some crystals. 

Bytownite crystals range from anhedral to subhedral. Irregular, poikilitic crystals similar to those described 

from ultramafic layers in the Archean Stillwater 

Complex (Hess, 1960, p. 21 and 113; Jackson, 1961, p. 66 

and 69) are scattered through hornblendite layers. They 

are believed to have grown largely from interstitial liquid 

and commonly contain small inclusions of euhedral 

hornblende. Bytownite replaces hornblende and is lobed 

against it; poikilitic crystals of bytownite in hornblendite, in particular, have grown around hornblende 

grains so that these grains project into bytownite (fig. 

57).

Hornblende forms irregular laths that on surfaces 

parallel to planar lamination form a network that surrounds and encloses bytownite grains. This network 

fabric is rarely evident on surfaces normal to lamination, 

however. Hornblende is pleochroic from light greenish 

yellow brown to dark green and contains innumerable 

Schiller-like inclusions that may be spinel. The inclusions are mostly confined to the interior parts of crystals 

and the borders are clear, suggesting that the latest 

formed hornblende has a slightly different composition.

FIGURE 57. Gabbro from the Riddle Peaks pluton, Holden and 

Lucerne quadrangles, showing poikilitic crystals of bytownite (B) 

that have grown around hornblende (H).

Hornblende was the first mineral to crystallize and 

shows no indication of being uralitic after pyroxene. 

Magnetite may form as much as 5 percent of some thin 

sections and is equally abundant in both hornblendic 

and anorthositic rocks; in fact, it is so abundant that the 

rock is highly magnetic. The magnetic forms small, 

anhedral, interstitial grains and was the last of the major 

constituents to crystallize. Pyrite is relatively abundant 

but there is little or no replacement of silicates by sulfides. Chlorite, having the optical properties of 

ripidolite, deserves special mention among the secondary minerals because of its occurrence as peculiar aggregates resembling a mass of rather stubby worms (fig. 

58). This crystal habit has been called helminth structure (Troger, 1967, p. 598). The helminth-structure aggregates occupy thin seams within the rock or replace 

hornblende. In cross section, individual worms form 

rather rounded hexagons.

Textures range from hypidiomorphic to xenomorphic. 

Hornblende and bytownite are seriate, and in all but 

pegmatitic varieties of gabbro these minerals rarely form 

grains more than 6 mm long. Poikilitic textures occur 

only in hornblendite layers where scattered anhedral 

grains of bytownite have engulfed numerous small 

crystals of hornblende, many of them euhedral. Similar 

poikilitic crystals of plagioclase and other minerals are 

characteristic of layered mafic intrusions (Hess, 1960; 

Brown, 1956; Jackson, 1961).

Because it seems fairly certain the pseudosedimentary 

features in the gabbro formed from a cumulate or 

magmatic sediment, the textures, whether hypidiomorphic or xenomorphic, are a measure of postsettling addiFiGURE 58. Chlorite having helminth structure in gabbro of the 

Riddle Peaks pluton, Holden and Lucerne quadrangles.
PRE-TERTIARY INTRUSIVE ROCKS 45

tion to or growth of originally euhedral grains. Thus, 

where textures are hypidiomorphic, secondary enlargement (Hess, 1939, p. 431; 1960; Brown, 1956, p. 37; 

Jackson, 1961, p. 47-52) was insufficient to fill completely the intercumulus space, and, consequently, 

mutual interference between settled crystals due to 

overgrowths was incomplete; much of the intercumulus 

liquid remained to crystallize as interstitial grains. On 

the other hand, where postsettling enlargement was such 

that the settled crystals grew to occupy virtually all the 

intercumulus space and mutual interference between 

grains was almost complete, the textures are 

xenomorphic. Hess (1939, p. 431; 1960) has attributed 

this process of postcumulus overgrowth and expulsion of 

the original intercumulus liquid to diffusion when 

crystal accumulation is slow, thereby providing an opportunity for settled crystals to interact with the bulk of 

the remaining magma rather than merely with the adjacent intercumulus liquid. The process seems to have 

been markedly effective in the Riddle Peaks gabbros 

because overgrowths have been sufficient to permit extensive interlocking of grains with the attendant 

tendency to xenomorphism; the plagioclase, furthermore, generally does not have the type of zoned rims that 

would be expected were the crystals subject to addition 

only from the intercumulus liquid. The complete lack of 

nonhydrous mafic minerals normally present in gabbros 

suggests an abnormal abundance of water in the magma, 

which may have augmented the process of diffusion and 

transfer of material.

The Riddle Peaks gabbro pluton differs from other 

layered gabbro masses of which I am aware in only one 

major respect, the utter lack of minerals of either the 

pyroxene or olivine groups a lack, incidentally, that is 

almost universally true of the other intrusive rocks in the 

area except for a few small, scattered masses of 

peridotite and serpentine. The role played by these 

anhydrous minerals has been entirely usurped by 

hornblende; biotite is a very minor mineral restricted to 

either pegmatitic or contaminated rocks. It could be 

argued, perhaps, that hornblende has replaced earlier 

mafic minerals, but not a shred of evidence could be 

found that pointed in this direction. The Schiller inclusions are not inherited at least intact from an earlier 

pyroxene because they follow crystal directions in the 

hornblende; no pseudomorphs after earlier crystals exist, 

and the hornblende inclusions in poikilitic bytownite are 

euhedral. Inasmuch as the gabbro consists essentially 

only of hornblende and bytownite in varying proportions, the small-scale layering is entirely rhythmic, and 

no phase contrast exists as in most layered masses.

As has been pointed out by numerous students of 

layered intrusions, most fully by Hess (1960, p. 

133-137), magmatic currents of variable velocities, 

probably convection currents, seem to be the only

satisfactory means of accounting for rhythmic layering. 

Both hornblende and bytownite were precipitated 

together throughout the crystallization of the Riddle 

Peaks mass because no layers are completely devoid of 

either mineral; therefore, ideas based on intermittent 

crystallization due to variations of pressure, gas escape, 

or extrusion of lava seem not to be applicable. As a matter of fact, both hornblende and bytownite precipitated 

at virtually equal rates throughout solidifying of the now 

visible parts of the mass, for the average composition of 

the rhythmic hornblendite and anorthosite pairs differs 

little, if at all, from the unlayered gabbro. Obviously, 

periods of current variability alternated with periods of 

current stability to produce the alternate zones of 

layered and unlayered rock, but I could find no evidence 

pointing to any specific cause for these oscillations.

The relatively even distribution of huge included 

blocks of metamorphic rocks throughout an exposed 

"stratigraphic" thickness of perhaps 2,500 m of layered 

and unlayered gabbro suggests that the specific gravity 

of the inclusions and the magma must have been similar. 

The fact that inclusions of all sizes are mostly surrounded by aureoles of contaminated and hybrid rocks 

also suggests long-continued contact with given volumes 

of magma, for rates of either rising or sinking were insufficient to sweep or scour away these aureoles. Of the inclusions examined, no trace of disturbance of underlying 

layers in the gabbro was detected; further evidence that 

the inclusions were little, if at all, denser than the 

magma. The aureoles were probably more viscous than 

the surrounding magma, which may have been the chief 

factor in inhibiting both layering and planar lamination 

adjacent to inclusions. Intuitively, one would think that 

an inclusion hundreds of feet across, even though of the 

same density as the magma, should have left some trace 

of its progress as it was dragged across the floor of settled 

crystals by magmatic convection currents; no traces 

were seen, but further search could perhaps reveal some.

The remarkably even and generally undisturbed layering and the planar lamination strongly suggest that 

crystal settling at now-visible levels occurred on only 

gently sloping surfaces. The exact position of the surviving gabbro relative to the entire pluton prior to its partial 

destruction by later intrusives is unknown, but the interlayered screens of gneiss along the northeast side of 

the remaining mass suggest that this is either part of or 

near the roof. The flattening of dips from southwest to 

northeast may indicate basining in that direction, but it 

may also merely be the result of postdepositional warping. In any event, the pluton as a whole has been faulted 

and rather steeply tilted northeastward since emplacement. Most of the faults strike northeast, but a large and 

complex northwest-trending breccia zone borders part of 

the pluton east of Fourth of July Basin. The breccia zone 

is largely confined to a screen of gneiss that separates the
46 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

gabbro from quartz monzonite of the Railroad Creek 

pluton; the breccia contains many fragments of quartz 

monzonite but few, if any, of gabbro.

The age of the Riddle Peaks gabbro pluton has not 

been determined. The oldest of the known intrusive 

rocks to cut it are the quartz diorites and granodiorites of 

the Cardinal Peak pluton, probably of Late Cretaceous 

age. The Cardinal Peak probably is not much younger, 

however, than the gabbro. There is little evidence to indicate that the Cardinal Peak was emplaced at any great 

depth and some to suggest only moderate or mesozonal 

depths, as, for example, the plagioclase that shows both 

patchy and some oscillatory zoning both are rarer 

among the older and deeper seated intrusive masses of 

the area.

120°45'

Unlayered 

gabbro

Layered gabbro

FIGURE 59. Map showing location of modally analyzed samples of 

gabbro from the Riddle Peaks pluton, Holden and Lucerne 

quadrangles. Sample analyses are given in table 16.

The location of modally analyzed specimens of gabbro 

from the Riddle Peaks pluton are shown in figure 59. 

Model analyses are given in table 16, and chemical and 

spectrographic analyses are given in table 17.

CARDINAL PEAK PLUTON

The Cardinal Peak pluton, probably of Late 

Cretaceous age, is a mass of highly variable rocks both in 

appearance and composition. It extends a known distance of 30 km from the northeast corner of the Holden 

quadrangle southeastward across the Lucerne quadrangle; its total length is not known. The maximum 

width within the mapped area is about 4 km. One small 

mass of similar rocks cuts the gabbro and gneiss of Riddle Peaks in Fourth of July Basin in the extreme 

northeast corner of the Holden quadrangle. As is true of 

the other narrow, elongate plutons in the area, the Cardinal Peak pluton trends nearly parallel to the strike of 

the enclosing metamorphic rocks but crosscuts them 

locally, particularly downdip.

The rocks of the Cardinal Peak pluton make up a sequence ranging from rather coarse-grained, light-colored 

biotite granodiorite to extremely heterogeneous contact 

complexes containing hornblende gabbro and hornblendite. Three principal units were delineated on the 

quadrangle maps. The largest unit, which makes up the 

bulk of the pluton, consists of rocks ranging from 

hornblende-biotite-quartz diorite to leucocratic biotite 

granodiorite; the second unit is confined to the 

northwesterly part of the pluton and consists of calcic 

hornblende diorite and quartz diorite; the third unit is 

the contact complex, which intermittently rims the 

pluton northwest of Snow Brushy Creek.

TABLE 16. Modal analyses of samples of hornblende gabbro from the Riddle Peaks pluton, central Washington

Sample 

No.

1

2

3

4

5

6

7

8

9

10

11

12

Plagioclase

46.7

45.0

48.8

45.6

42.2

57.7

57.0

44.4

53.0

60.7

75.7

71.1

Magnetite

0

2.6

0

2.1

0

5.0

.2

6.0

0

5.2

2.6

4.4

Quartz

0

0

0

0

0

0

0

0

0

0

.7

0

Biotite

0

0

0.1

0

0

0

0

0

0

0

.2

0

Hornblende

52.4

48.4

50.4

52.3

54.7

37.3

42.2

48.6

42.4

33.9

20.4

24.4

Accessory 

and secondary minerals

0.9

4.0

.7

0

3.1

0

.6

1.0

4.6

.2

.4

.1

Total 

mafic 

minerals

53.3

55.0

57.2

54.4

57.8

42.3

43.0

55.6

47.0

39.3

23.6

28.9

Anorthite in 

plagioclase crystals (percent)

Average

75

67

74

78

73

64

78

60

71

64

58

53

Core

0

0

84

83

77

70

80

70

0

0

71

69

Rim

0

0

68

75

71

60

65

55

0

0

51

47

Remarks

Xenomorphic.

Do.

Do.

Hypidiomorphic.

Xenomorphic.

Do.

Hypidiomorphic; planar

orientation of crystals.

Hypidiomorphic; subparallel horn

blende and plagioclase crystals.

Xenomorphic; parallel

orientation of crystals.

Hypidiomorphic.

Xenomorphic.

Hypidiomorphic .
PRE-TERTIARY INTRUSIVE ROCKS 47

TABLE 17. Chemical and spectrographic analyses of a composite 

sample of hornblende gabbro from the Riddle Peaks pluton, central 

Washington

[Standard chemical analysis by Edythe Engleman. Spectrographic analysis by B. W. 

Lanthorn. Leaders (- - -), below sensitivity limit]

Chemical analysis (percent)

SiC-2 ----------

A1203 ----------

Fe 2O3 ---------

T7«/^

MgO ----------

CaO

Na2O----------

K2O-----------

H r"\_L

H f\

T1C\

P2 05 --------- 

MnO ---------- 

C02 ----------- 

d ------------ 

F ------------- 

Zn ------------ 

Total------

-----..... 45.08

99 fin

0. CO

---------- 5 24

c 40

n

CH

9 P,^

00.

1 CO

------ . OQ

1 °,1

----.-.... .16 

-.----.... .10 

-----..... .01 

-----..... .02 

.......... .05

......... 100.09

Spectrographic

Co -----------

Cr -----------

Cu-----------

Ni -----------

o

Qr

V ------------

Zr -----------

Ga-----------

Yb-----------

analysis (percent)

.... 20

.............. 7

Of)

1C

Or)

i non

onn

90

--------.-20

or)

0.

HORNBLENDE-BIOTITE-QUARTZ DIORITE 

AND BIOTITE GRANODIORITE

Rocks ranging from hornblende-biotite-quartz diorite 

to leucocratic biotite granodiorite form most of the 

pluton and change in both composition and appearance 

from northwest to southeast. At the northwest end of the 

pluton in the valley of Tenmile Creek, the rocks are 

rather dark-gray, medium-grained, massive or foliated 

hornblende-biotite-quartz diorite (fig. 60). South of 

Railroad Creek, however, the rock becomes lighter in 

color, coarser grained, and tends toward a flaser appearance because of moderate protoclasis. Some of these 

rocks contain sufficient potassium feldspar to classify 

them as granodiorite. Southeastward from the vicinity of 

the lakes at the head of Dole Creek, protoclasis intensifies, and the rocks become typical flaser gneisses. In 

the vicinity of Milham Pass, protoclasis is so extreme 

that the rocks superficially resemble dark porphyries; 

rounded, white porphyroclasts (fig. 61) of plagioclase as 

much as 7 mm across are embedded in a black, nearly 

aphanitic groundmass of almost phyllitic texture. South 

of Saska Peak, the rock becomes less protoclastic and 

gradually changes into a light-colored, coarse-grained 

biotite granodiorite flaser gneiss near Cardinal Peak, 

and from Pyramid Mountain southeastward it changes 

into a coarse-grained, leucocratic, nearly massive rock 

showing only incipient protoclasis (fig. 62). In general, 

the foliation resulting from protoclasis parallels the 

structure of the metamorphic host rocks, but at 

numerous localities along the contact the foliation is at a 

small angle to the contact, although parallel to the 

regional foliation of the host rocks or, more commonly, at

i;v t .

# &

ft, ,5 .

: -ei>, " . frypF--*^ i%l^ S- ~

 "-.. ^Jfc^l___

 >*- T^«Mii

* Jv-f . i <**# *

FIGURE 60. Foliated hornblende-biotite-quartz diorite from the 

Cardinal Peak pluton, Lucerne quadrangle.

an angle to the regional foliation or to both the contact 

and the regional foliation. In many places, protoclastic 

foliation is swirled and irregular.

Inclusions are not abundant in this main unit, but 

fragments and schlieren derived from various 

metamorphic rocks and numerous chunks of hornblende 

gabbro from the Riddle Peaks pluton occur locally, particularly near contacts northwest of Saska Peak. Some 

blocks of hornblende gabbro as much as 12 m across were 

seen between the lakes at the head of Dole Creek and 

Railroad Creek. Most inclusions of all kinds show only 

minor effects from immersion in the Cardinal Peak 

magma.

In the area between the lakes at the head of Dole Creek 

and Cardinal Peak where protoclasis is most extreme are 

peculiar spindle- and canoe-shaped masses ranging from 

30 cm to a few meters across and from a few meters to a 

few tens of meters long that are either partly or completely enveloped by sheets or rinds of greenish-gray, 

fine-grained, sheared material, similar to the protoclastic groundmass of the pseudoporphyries of the area. 

The canoe-shaped masses occur in crests of folds in the 

protoclastic foliation, whereas the spindle-shaped 

masses appear to be completely enveloped in rinds of
48 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

FIGURE 61. Quartz diorite from the Cardinal Peak pluton, Lucerne 

quadrangle, showing a pseudoporphyritic appearance resulting from 

extreme protoclasis.

FIGURE 62. Biotite granodiorite from the Cardinal Peak pluton, 

Lucerne quadrangle, showing only slight flaser texture.

sheared material. The interior parts of the masses are 

identical to the rest of the quartz diorites and 

granodiorites. These masses seemingly formed in 

response to differential shearing stresses as the crystal

mush of the pluton was intruded; the spindle-shaped 

masses appear to have behaved much as roller bearings. 

It should be stressed at this point, however, that under 

the microscope, the last minerals to form in the sheared 

rinds, such as oligoclase overgrowths on shattered 

crystals of andesine, -fine-grained hornblende, and 

biotite are mostly undeformed and show no indication of 

having crystallized under differential stress. Some of 

these masses are flat lying, but most dip south at angles 

of as much as 15° parallel to the plunge of elongate 

mineral clusters and elongate grains.

The contacts of quartz diorite and granodiorite with 

both metamorphic host rocks and with other units of the 

pluton are as diverse as the other aspects of the pluton. 

As has been previously mentioned, the northwestern 

part of the pluton is partly rimmed by contact complexes, described below, but the contact between these 

complexes and the main unit shows considerable variation. In many places, the rocks of the main unit seem to 

grade into or are intermixed with the extremely 

heterogeneous rocks of the contact complexes; in other 

places, main-unit rocks cut the complexes, and in still 

others, some rocks of the complexes intrude main-unit 

rocks. Where contacts between quartz diorite and 

granodiorite of the main unit and the calcic hornblende

diorite and quartz diorite were observed, the calcic 

rocks are later, but field relations such as lack of angular 

inclusions of quartz diorite and granodiorite and the 

generally vague contacts between the two rock types suggest they are not much later. Where main-unit rocks are 

in direct contact with metamorphic host rocks, the contacts may be sharp, gradational, or form lit-par-lit zones 

of gneiss and quartz diorite or granodiorite. Such lit-parlit zones should not be confused with the contact complexes, however, which are entirely different. 

Gradational contacts are less common than either those 

that are sharp or consist of lit-par-lit zones. Gradational 

zones between visually unaltered metamorphic rocks 

and igneous rock typical of the pluton are not more than 

several meters thick and generally are much thinner. In 

places, particularly along sharp contacts, the adjoining 

gneisses are much crumpled.

CALCIC HORNBLENDE DIORITE AND QUARTZ DIORITE

Calcic hornblende diorite and quartz diorite are of 

fairly common occurrence northwest of Snow Brushy 

Creek but are rare south of there, and no masses of sufficient size to map were seen. Most of these rocks are 

confined to the periphery of the pluton and commonly 

form one of the major constituents of contact complexes, 

but one sizable, dikelike mass crops out along the crest of 

the ridge between the Entiat River and Klone Creek. 

Other smaller, unmapped masses also occur at interior 

positions within the pluton. The rock is gray and ranges
PRE-TERTIARY INTRUSIVE ROCKS 49

from rather fine grained, where few grains are more than 

1 mm across, to medium grained, where hornblende 

forms blades 5 mm long. Most of the rock is massive and 

structureless, but some has a gneissic appearance 

because of protoclasis. Because of their mineralogical 

and compositional differences and, so far as known, a 

lack of varieties intermediate with main-unit rocks of the 

pluton, the possibility exists that these rocks bear little 

direct relation to the pluton other than a spatial one. 

Most likely, however, these factors are of less 

significance than the close spatial association of the 

rocks with the pluton, the close and intricate 

relationship to the contact complexes, and what locally 

appears to be marble-cake intermixing of main-unit 

rocks and the calcic hornblende diorite and quartz 

diorite.

CONTACT COMPLEXES

Rocks of the contact complexes closely resemble those 

associated with the White Mountain and Seven-fingered 

Jack plutons and are equally heterogeneous and wildly 

scrambled (figs. 63, 64). Because of the extreme 

heterogeneity, proportions of various rock types are difficult to estimate, but most abundant are hornblende 

diorites and gabbros of varied textures that range from 

fine grained to coarsely pegmatitic and have hornblende 

blades 5 to 8 cm long (fig. 63). Each of the textural variations grades into one or more of the others, although 

locally, contacts between types are sharp. Less abundant 

are rocks more typical of the interior of the pluton that 

are intricately interinjected into the more calcic rocks. 

Inclusions of several kinds of gneiss and schist oriented 

in all directions and in various states of assimilation, 

make up a considerable proportion of the complexes (fig. 

64), but probably most characteristic are irregular 

masses of hornblendite a number of centimeters to 

several meters across. The hornblendites range from 

medium grained to very coarse grained, and crystal 

shapes range from stubby to bladed. Many grade outward from pure aggregates of hornblende into gabbros as 

proportions of labradorite increase, but other masses of 

pure hornblendite are sharply bounded. These mixtures 

of rock are cut by anastomosing dikes of the calcic 

hornblende diorite and quartz diorite described in the 

preceding paragraph. Contacts between these dikes and 

the remainder of the complexes may be either gradational or sharp.

Contact complexes in some places intrude metamorphic host rocks with no zone of gradation between 

them, but more commonly the heterogeneous mass of 

material in the complexes grades into the host rocks 

through an increase in the amount of included material, 

which in turn grades into a zone of host rocks cut by 

anastomosing dikes of igneous material.

FIGURE 63. Contact complex of Cardinal Peak pluton, Lucerne 

quadrangle, consisting largely of gabbro. Note large hornblende 

crystals (hbld).

FIGURE 64. Contact complex of Cardinal Peak pluton, Lucerne 

quadrangle, showing inclusions of metamorphic rocks, gabbro, and 

hornblendite in a matrix of quartz diorite.
50 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Origin of the hornblendite inclusions is not well understood. No hornblendite masses other than the thin layers 

in the Riddle Peaks plutons and those in the various 

other contact complexes exist in the region, so it seems 

highly unlikely they could have been torn from such 

masses. More likely, they result from interaction of 

magma and inclusions torn from probably hornblendic 

varieties of metamorphic rocks. Many inclusions of 

hornblende gneiss have rims from which felsic material 

has been removed; complete removal would, of course, 

have produced hornblendite but would not explain the 

coarse-grained nature so typical of most hornblendite inclusions. Perhaps crystal growth resulted from the 

mildly pegmatitic environment in which the complexes 

formed.

PETROGRAPHY

Thin-section examination revealed many differences 

between the major units of the Cardinal Peak pluton, 

but within these units, variations from place to place of 

some magnitude also exist. Differences are most marked 

in hornblende-biotite-quartz diorite and the biotitequartz diorite and granodiorite of the main unit. All 

these rocks contain andesine, quartz, and biotite, but 

only those northwest of Cardinal Peak contain more than 

traces of hornblende. Orthoclase, on the other hand, may 

or may not occur in rocks northwest of here (and mostly 

only in small amounts), but to the southeast it is a constant constituent, in places in sufficient quantity to classify the rocks as granodiorite. Apatite, opaque minerals, 

and titanite are accessory in all thin sections; a little 

clinopyroxene was seen in a few, and a single grain of allanite in one. Most of the rocks are fresh, although small 

amounts of chlorite, sericite, and clinozoisite-epidote occur in all.

Andesine makes up roughly half of the main-unit 

rocks. Northwest of Emerald Peak the average composition is close to An4o, but cores of some grains are sodic 

labradorite. Southeast of Emerald Peak, andesine 

gradually and irregularly becomes less calcic so that 

from the vicinity of Cardinal Peak southeastward the 

average composition is about An, , although cores of 

some crystals are as calcic as those to the northwest. 

Andesine, having crystallized early, nearly everywhere 

shows the effects of protoclasis; grains are rounded, 

abraded, and distorted, and most are cracked into 

groups of individual fragments that are slightly rotated 

with respect to each other. Most porphyroclasts show a 

few oscillatory zones, and patchy zoning is ubiquitous. 

Thin overgrowths of calcic oligoclase have formed on 

many crystals subsequent to distortion and abrasion; 

furthermore, much of the fine-grained plagioclase in the 

matrix between the porphyroclasts is calcic oligoclase.

Quartz in the few nonprotoclastic rocks is interstitial

or replaces the earlier formed andesine, but in the 

protoclastic rocks it forms anastomosing irregular seams 

and lentils of tiny interlocking grains that wrap around 

the porphyroclasts. These aggregates of interlocking 

quartz grains seem to have excluded other minerals in 

the protoclastic matrix so that the matrix does not consist of evenly distributed aggregates of various minerals. 

Orthoclase also is interstitial or forms irregular seams 

that partly replace plagioclase; it is most abundant in 

rocks where chlorite has extensively replaced mafic 

minerals and is commonly associated with chlorite.

Hornblende and biotite differ somewhat in their mode 

of occurrence and relation to protoclasis. Where present, 

hornblende crystallized earlier and generally formed 

larger grains that show the effects of protoclasis but not 

to the extent that andesine does. Much of it, however, is 

in the fine-grained matrix and seems to have formed 

after protoclasis largely ceased. Very few of the larger 

grains retain crystal faces; the fine-grained hornblende 

in the matrix material is decidedly shredlike but little 

deformed. Pleochroic colors mostly range from light yellowish brown to green. Biotite, on the other hand, mostly 

occurs as small, largely undeformed flakes and shreds in 

the groundmass. Some of it is euhedral but most is not. 

It is pleochroic from straw yellow to dark brown.

Textures range from hypidiomorphic granular to intensely protoclastic. In some places, protoclasis grades 

into cataclasis where even the latest formed minerals are 

deformed and shattered.

Calcic hornblende diorite and quartz diorite differ 

mainly in the abundance of quartz, and diorite is far less 

common than quartz diorite. All the rocks contain 

plagioclase, hornblende, and biotite as major constituents and all also contain at least some quartz. 

Orthoclase, titanite, apatite, and opaque minerals are 

accessory, and chlorite and epidote are secondary. Calcic 

andesine usually constitutes from 55 to 65 percent of the 

rock. The average composition of the plagioclase is 

rather difficult to estimate because of the large numbers 

of oscillatory zones, which range from some cores as 

calcic as An70 to rims that are less than An4 o- Patchy zoning is also common, which adds to the risks of estimating 

compositions, but in general the plagioclase probably 

averages An4s to Anso . Crystals are subhedral to euhedral 

and, in many places, have a subparallel alinement 

resulting from flowage.

Quartz is interstitial, but in protoclastic rocks it occurs as irregular lentils of interlocking grains. The accessory orthoclase occurs interstitially or as fine seams that 

cut plagioclase.

Hornblende occurs as subhedral to anhedral blades 

and shreds as much as 4 mm long that are pleochroic in 

shades of light yellowish brown to green. Biotite forms 

anhedral shreds pleochroic from light straw yellow to 

bright reddish brown, a feature that combined with more
PRE-TERTIARY INTRUSIVE ROCKS 51

calcic plagioclase serves to distinguish this rock from 

similar appearing dikes of late Eocene hornblendebiotite-quartz diorite. Much of the biotite replaces 

hornblende, and chlorite replaces small amounts of both 

minerals.

Textures are hypidiomorphic granular generally; some 

thin sections also have flow textures defined by subparallelism of elongate grains. Protoclasis is visible in 

some sections but is nowhere as extreme as in rocks of 

the main units.

Rocks of the contact complex show so many variations 

in thin section that a description of even part of them 

would require a great deal of space to no particular purpose. Many that in outcrop appear to be straightforward 

igneous rocks, in thin section are seen to be hybrid rocks 

containing crystals derived from invaded rocks, as, for 

example, hornblende crystals obviously derived from 

hornblende gabbro of the Riddle Peaks pluton. Most

characteristic and invariably present are gabbroic rocks 

containing sodic labradorite showing both oscillatory 

and extreme patchy zoning, hornblende, biotite, and 

commonly a little quartz, and accessory magnetite, 

apatite, and titanite. The minerals in the gabbros are 

variable in composition and habit. Hornblende is 

pleochroic in yellows, greens, and browns, and many 

crystals are irregularly zoned. Biotite is pleochroic from 

straw yellow to bright brownish red or to very nearly 

opaque muddy brown. Textures range from xenomorphic 

to hypidiomorphic; some rocks show flow textures, and 

others are protoclastic.

Modal analyses of rocks from the Cardinal Peak 

pluton are shown in table 18 and chemical analyses in 

table 19. The locations of modally analyzed specimens 

are shown in figure 65. Modes are plotted in figure 66, 

and the major oxides are plotted in the variation 

diagram (fig. 13).

TABLE 18. Modal analyses of samples of diorite, quartz diorite, and granodiorite from the Cardinal Peak pluton, Lucerne quadrangle

[Leaders (- - -), unable to determine]

Sample 

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

Plagioclase

50.4

44.5

61.3

64.8

54.1

55.9

54.5

59.3

65.2

66.6

54.1

43.3

53.9

53.0

38.6

47.6

52.2

35.6

49.1

54.2

57.3

59.0

64.8

58.5

61.4

61.3

63.2

58.8

Potassium 

feldspar

2.3

.9

1.3

.4

1.9

0

.9

.4

.1

0

0

0

0

0

0

0

5.2

1.4

1.3

0

1.4

1.8

4.5

1.7

2.6

2.6

2.1

0

Quartz

28.3

8.2

23.9

17.5

29.3

17.2

27.1

32.3

15.2

2.3

14.3

19.1

10.2

6.5

4.3

4.0

28.0

28.4

42.7

25.3

21.3

28.5

15.1

18.6

19.7

16.4

15.4

18.0

Biotite

8.8

3.6

6.6

11.7

12.5

7.1

11.2

1.7

0

24

12.1

10.4

8.5

3.2

4.6

1.0

9.1

14.8

5.1

8.3

12.3

8.4

13.0

14.3

7.2

15.5

9.3

1.5

Hornblende

2.6

37.7

2.6

3.5

.8

14.8

4.5

3.6

8.2

20.3

18.0

25.6

26.6

34.0

49.3

44.1

0

17.1

0

8.9

3.6

0

0

5.0

0

0

0

0

Accessory 

and secondary minerals

7.6

5.1

4.3

2.1

1.4

5.0

1.8

1.7

10.3

8.2

1.5

1.6

.8

3.3

3.2

3.3

5.5

2.7

1.8

3.3

4.1

2.3

2.6

6.9

9.1

4.2

10.0

21.7

Total 

mafic 

minerals

18.6

46.4

13.5

17.3

14.7

26.9

16.5

7.0

18.5

31.1

31.6

37.6

35.9

40.5

57.1

48.4

14.6

34.6

6.9

20.5

20.0

10.7

15.6

21.2

16.3

19.7

19.3

23.2

Anorthite in 

plagioclase crystals (percent)

Average

37

38

40

40

41

51

39

40

50

52

50

37

40

47

44

54

33

35

27

34

34

33

33

34

33

34

33

32

Core

43

46

51

43

47

54

50

53

59

...

70

43

44

53

76

...

60

29

43

41

38

39

39

38

41

39

43

Rim

31

23

23

31

34

38

27

37

22

...

40

23

38

30

...

31

...

23

24

31

28

27

17

24

26

23

19

22

Remarks

Protoclastic.

Do.

Do.

Hypidiomorphic .

Protoclastic.

Quartz gabbro in contact

complex; hypidiomorphic.

Protoclastic.

Xenomorphic seriate.

Quartz gabbro in contact

complex; hypidiomorphic.

Quartz gabbro in contact

complex; hypidiomorphic.

Hypidiomorphi c .

Xenomorphic.

Protoclastic.

Do.

Do.

Hypidomorphic.

Porphyroclastic.

Do.

Do.

Protoclastic;

accessory augite.

Hypidiomorphic; protoclastic.

Protoclastic.

Do.

Protoclastic-hypidiomorphic.

Hypidiomorphic.

Do.

Hypidiomorphic-protoclastic.

Hypidiomorphic.
52 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 19. Chemical and spectrographic analyses and norms of 

composite samples of rocks from the Cardinal Peak pluton, Lucerne 

quadrangle

[SiO2 and AUOs determined colorimetrically; FeO determined volumetrically; FegOa, MgO, 

CaO, and Mn determined by atomic absorption; Na2O and I^O determined by flame 

photometer. Analysts: Wayne Mountjoy, J. D. Mensik, Claude Huffman Jr., G. T. Burrow, 

and H. H. Lipp. Spectrographic analyses by Barbara Tobin. N.d., not detected]

Sample -------------------- 1 2

Chemical analyses (percent)

SiO2 ---------------------- 66.9 65.3

A12O3 ---------------------- 16.5 18.5

Fe2O3 --------------------- 1.26 1.38

FeO----------------------- 2.21 2.44

MgO---------------------- .96 .93

CaO ---------------------- 4.1 5.0

Na20---------------------- 4.36 4.55

K2O----------------------- 1.61 1.17

Mn ----------------------- .061 .092

Total------------------ 98 99

Semiquantitative spectrographic analyses (parts per million)

Ba ------------------------ 1,000 700

Co ------------------------ 15 15

Cr ------------------------ 50 7

Cu------------------------ 100 100

Ga------------------------ 50 30

Ni ------------------------ 20 N.d.

Sc ------------------------ 10 15

Sr ------------------------ 1,500 1,000

V------------------------- 100 100

Y ------------------------- 10 15

Yb------------------------ 1.5 1.5

Zr ------------------------ 70 50

Norms

q ...---.----..--.---.---.. 24.25 20.82

or------------------------- 9.71 6.96

ab ------------------------ 37.64 38.72

an ------------------------ 20.76 24.96

hy ------------------------ 5.63 5.86

c .......................... .14 .67

mt ------------------------ 1.87 2.01

Total------------------ 100.00 100.00

Plagioclase composition

an ------------------------ 35.5 39.2

Sample descriptions

1. Composite, protoclastic hornblende-biotite-quartz diorite.

2. Composite, nonprotoclastic hornblende-biotite-quartz diorite.

120°45' 120°30'

FIGURE 65. Map showing location of modally analyzed samples of 

quartz diorite and granodiorite from the Cardinal Peak pluton, 

Holden and Lucerne quadrangles. Sample analyses are given in 

table 18.

Plagioclase

Potassium 

feldspar

FIGURE 66. Plot of modes of diorite, quartz diorite, and granodiorite 

samples from the Cardinal Peak pluton, Holden and Lucerne 

quadrangles, on a quartz-potassium feldspar-plagioclase diagram. 

Sample analyses are given in table 18.
TERTIARY INTRUSIVE ROCKS 53

TERTIARY INTRUSIVE ROCKS

Intrusive rocks of Tertiary age crop out extensively in 

the study area and elsewhere in the northern Cascade 

Range. Those in the study area are of three known ages, 

early Eocene, late Eocene, and Miocene; many additional dikes may be of other ages. The intrusives of 

early Eocene age are volumetrically minor and consist 

of four small stocks in the vicinity of Clark Mountain. 

Plutons of late Eocene age crop out extensively in the 

Lucerne and eastern part of the Holden quadrangles. 

The Miocene intrusions consist of a sizeable batholith, 

the Cloudy Pass, and a number of related plugs and 

masses of intrusive breccia.

Most of the Tertiary intrusions are somewhat elongate 

parallel to the regional trend of the metamorphic host 

rocks, and one, the large upper Eocene Duncan Hill 

pluton, resembles a greatly thickened dike as do so many 

of the pre-Tertiary intrusions. Overall compositions do 

not differ greatly from pluton to pluton but can range 

from gabbro to quartz monzonite within a single mass. 

Granodiorite, however, is most abundant and gabbro the 

least.

EARLY EOCENE INTRUSIVE ROCKS

CLARK MOUNTAIN STOCKS

In the vicinity of Clark Mountain in the southwestern 

part of the Holden quadrangle, four small stocks of 

quartz diorite and granodiorite crop out, no one of which 

underlies an area exceeding 2 km2 . The stocks are, in 

part, structurally controlled and tend to be elongated in 

the direction of host-rock trends. Locally they deflect 

and wedge apart the host rocks, but mostly they cut out 

large thicknesses of them. Contacts almost everywhere 

are sharp, although zones of interlayered intrusive 

material and schist or gneiss several tens of meters 

across occur, particularly where contacts are transgressive as in the area about 3 km east of Clark Mountain. In 

general, granodiorite and quartz diorite have been injected along planes of foliation and commonly wedge 

apart layers of schist and gneiss, but irregular dikes and 

apophyses trangress foliation. Near contacts, the stocks 

contain many inclusions showing various stages of assimilation; some of these resemble autoliths, whereas 

others are disoriented fragments of local wall rock. 

Rarely do the wall rocks show megascopically discernible 

contact effects; even marble, where cut by the intrusives, 

is virtually unmodified. Locally, aplite dikes are abundant in the vicinity of contacts.

In outcrop appearance there is no perceptible difference between granodiorite and quartz diorite; both

-^

FIGURE 67. Hornblende-biotite granodiorite from the Clark 

Mountain stocks, central Washington.

are gray, medium-grained, massive rocks of uniform appearance (fig. 67), although in places an obscure lineation is visible. The rock consists of 45 to 55 percent 

plagioclase, 20 to 26 percent quartz, 13 to 16 percent 

biotite, 0.2 to 10 percent potassium feldspar, and 0 to 2.5 

percent hornblende. Accessory titanite occurs in 

amounts as high as 1.6 percent; apatite, magnetite, and 

zircon are less plentiful. Secondary minerals are 

clinozoisite-epidote, chlorite, and sericite.

Plagioclase crystals are commonly 1 to 3 mm across 

and range in composition from Ani8 on the rims of some 

crystals to An<o in the cores of the more calcic grains. 

The average composition varies little from place to place 

and is uniformly An2 9 to An3 o and thus is either calcic 

oligoclase or sodic andesine. Many crystals show wellformed crystal outlines, and oscillatory zoning is common except in very small grains or where zoning has been 

destroyed by twinning; not uncommonly adjacent twin 

lamellae vary by as much as 3 or 4 percent in composition in sections where zoning has been destroyed. Patchy 

zoning is a common feature. Albite twinning is not as 

common as poly synthetic twinning on the 001 plane. A 

small amount of albite forms discontinuous, thin, clear 

rims on microcline and appears to be the result of exsolution. Myrmekite is also common in sections containing 

considerable microcline, especially on the rims of 

plagioclase crystals bordering microcline. Quartz occurs 

interstitially and as irregular grains; curved lines of tiny 

liquid inclusions occur in larger grains of quartz. Biotite 

occurs as small, irregular shreds and as well-formed 

crystals as much as 3 mm across. Some of the biotite 

replaces hornblende, but the coarser grains are primary; 

much of the fine-grained biotite appears to be later than 

quartz. Orthoclase and microcline commonly occur in irregular grains and as interstitial material. Both are most 

abundant along lines or zones of incipient fracturing and 

replace all other primary minerals. Hornblende is sparse,
54 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

and most is extensively replaced by biotite. Of the accessory minerals, titanite is by far the most abundant and 

commonly occurs in two forms: as rhombs as much as 2 

mm long and as irregular grains in and bordering biotite. 

These irregular grains associated with biotite formed 

during the replacement of hornblende by biotite, apparently because the biotite was unable to accommodate 

as much titanium as was hornblende.

The secondary minerals, clinozoisite-epidote, sericite, 

and chlorite are invariably present, although only 

clinozoisite-epidote occurs in amounts exceeding 1 percent. Most of the clinozoisite-epidote occurs as relatively 

well formed crystals as much as 0.3 mm long that replace 

plagioclase. Not uncommonly, these crystals are concentrated as clusters in the cores of plagioclase crystals. Chlorite replaces biotite, and sericite replaces 

plagioclase.

The texture of the quartz diorite and granodiorite is 

hypidiomorphic granular with protoclastic modifications. Potassium metasomatism is indicated by the 

concentration of potassium feldspar along zones of deformation; in none of the sections examined is potassium 

feldspar deformed or granulated, although adjacent 

plagioclase, quartz, and biotite are crushed and abraded.

Engels (Engels and others, 1976) obtained potassium/argon ages of about 57 m.y. from biotite and 59 

m.y. from muscovite in the Clark Mountain rocks (table 

39).

Modal analyses of rocks from the Clark Mountain 

stocks are given in table 20 and chemical and 

spectrographic analyses and norms in table 21; the major 

oxides are plotted on a variation diagram (fig. 70). Locations of modally analyzed specimens are shown in figure 

68; a plot of the modes is presented in figure 69; and the 

norms in figure 71.

LATE EOCENE INTRUSIVE ROCKS

Intrusive rocks of late Eocene age crop out extensively 

in the Lucerne and eastern part of the Holden 

quadrangle and are common elsewhere in the northern 

Cascades. Within the report area, they range in composiTABLE 21. Chemical and spectrographic analyses and norms of a 

composite sample of biotite granodiorite from the Clark Mountain 

stocks, Holden quadrangle

[Standard rock analysis by D. F. Powers. Spectrographic analysis by P. R. Barnett]

Chemical analysis 

(percent)

SiO2 ---------

Fe2O3 --------

IV-lgV-' 

PaO

K c\

H

/-\ i

H

r~v

P2 05 -------

MnO ---------

£ £ OC

- 16.09 

- .74 

- 3.07 

- 1.53 

4.30 

4.01 

1.93 

- .65 

- .07 

- .74 

.21 

- .06 

.03

99.69

Semiquantitative 

spectrographic 

analysis (parts per million)

Ba

Co 

Cr 

Cu 

Ga 

La 

Ni 

Sc 

Sr 

V -

Y -

Zr

700

q

1 f\

........... 7

........... 15

----------- 30

q

........... 7

i coo

.._--_-__ 70

...-------. 7

ICO

Norms

q ...........

ah

hy ..........

ap

Total ------

oq 91

n

co

Q A OC

1Q Q7

7 Cft

-- .17

1

f\Q

-- 1 49

co

-- .07

- 100.00

Plagioclase composition

O/? 0

tion from quartz gabbro to quartz monzonite, but 

granodiorite is most abundant and quartz gabbro least 

abundant. In fact, the single most characteristic feature 

of upper Eocene and younger rocks is the presence of 

considerable potassium feldspar, a rare constituent in 

older intrusions.

The intrusive rocks form plutons of various shapes and 

sizes, large numbers of dikes, and a volcanic neck. The 

largest of the plutons that project into the mapped area 

is the Duncan Hill pluton, a mass about 48 km long and 

at least 9.6 km wide. This mass and some of the smaller 

ones parallel the strike of the metamorphic host rocks, 

but other masses are irregular and are unrelated to 

regional structural trends.

Some of the masses consist almost entirely of a single 

rock type, whereas others, particularly the Duncan Hill, 

contain rocks of diverse compositions. In a given pluton, 

contacts between rocks of different composition may be 

gradational or they may form complexes of sharply

TABLE 20. Modal analyses of samples of biotite-quartz diorite and granodiorite from the Clark Mountain stocks, Holden quadrangle

Sample 

No.

1

2

Plagioclase

51.3

50.6

Potassium 

feldspar

0.1

.2

Quartz

19.8

23.2

Biotite

10.5

15.7

Hornblenc

12.8

2.5

Accessory

and secondle ary minerals

5.5

7.8

Total

mafic 

minerals

28.8

26.0

Anorthite in

plagioclase crystals (percent)

Average

37

29

Core

40

32

Rim

35

20

Remarks

Hypidiomorphic .

Hypidiomorphic; coarse,

euhedral clinozoisite. 

53.5 8.2 20.7 13.1 .1 4.4 17.6 30 40 18 Hypidiomorphic;

abundant sphene.

52.3 .6 21.1 20.8 0 5.2 26.0 34 42 20 Hypidiomorphic. 

45.3 3.3 25.2 - 1.7 0 11.5 26.2 29 34 27 Hypidiomorphic; coarse,

euhedral clinozoisite.
TERTIARY INTRUSIVE ROCKS 55

121°00'

48' 

02' 

10"

Q

0 2 KILOMETERS

FIGURE 68. Map showing location of modally analyzed samples of 

biotite-quartz diorite and granodiorite of the Clark Mountain stocks, 

Holden quadrangle. Sample analyses are given in table 20.

Quartz

____________________ ____ Potassium 

Plagioclase 5 35 feldspar

FIGURE 69. Plot of modes of biotite-quartz diorite and granodiorite 

samples from the Clark Mountain stocks, Holden quadrangle, on a 

quartz-potassium feldspar-plagioclase diagram. Sample analyses are 

given in table 20.

bounded, separate intrusions. Where order of emplacement within a pluton is determinable, it is usually of increasing silica and alkali content with decreasing age, 

but probably because rocks of different composition were 

simultaneously molten, the orders of intrusion may differ from one locality to another or even in the area of a

o Clark Mountain stocks

 Duncan Hill pluton

D Larch Lakes pluton

X Old Gib volcanic neck

EXPLANATION 

+

201 

CJ

£8 o

Hornblende-biotitequartz diorite 

A Railroad Creek pluton

* Holden Lake Pluton

o Biotite-quartz monzonite

 f 

10 r5 | 

 x

,o

10

 ° X +

50 60 70 

SiO2, IN WEIGHT PERCENT

80

FIGURE 70. Variation diagram of major oxides in rock samples from 

Eocene plutons, Holden and Lucerne quadrangles.
56 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Quartz

Quartz monzonite. Rampart

Mountain pluton 

Hornblende- / 

biotite-quartz / Biotite-quartz 

/ /monzonite

/Granodiorite, Railroad 

* Creek pluton

Dacite, Old Gib 

volcanic neck

Granodiorite, Clark 

Mountain stocks Granodiorite, Larch 

Lakes pluton

Quartz gabbro, Holden Lake pluton

__^ Potassium

Plagioclase 5 35 feldspar 

FIGURE 71. Plot of norms of samples from small Tertiary intrusives,

Holden and Lucerne quadrangles, on a quartz-potassium feldsparplagioclase diagram.

single large outcrop. Relative ages of some of the larger 

intrusions are not determinable because they are not in 

mutual contact, or contacts were not observed; this was 

particularly true of contacts of the Larch Lakes and 

Rampart Mountain plutons with other large masses.

Radiometric ages of late Eocene intrusive rocks are in 

a fairly narrow range; the oldest pluton, the Duncan 

Hill, gave potassium/argon ages ranging from 43 m.y. to 

46 m.y., the 46-m.y. date coming from the granophyritic 

rocks on Stormy Mountain at the shallow, hypabysal 

end of the pluton (Engels and others, 1976). Ore in the 

Holden mine replaces Duncan Hill rocks, and phlogopite 

gangue in the ore is about 44 m.y. old (Engels and others, 

1976). The youngest of the larger upper Eocene plutons, 

the Railroad Creek, yielded ages of about 42 and 43 m.y. 

(Engels and others, 1976). Other late Eocene intrusions 

are in between in that they cut the Duncan Hill and are 

cut by the Railroad Creek. All post-Duncan Hill rocks 

that are exposed in the Holden mine also contain inclusions of ore, whereas ore replaces Duncan Hill and older 

rocks. Sulfides in some of the inclusions had been 

mobilized and sent short veinlets out into the engulfing 

rock.

MINERALOGY

The mineral content of the various rocks is similar. It 

consists of varying proportions of plagioclase, quartz, 

and biotite in all the rocks and either potassium feldspar

or hornblende, or both, in most of them. Mineralogic differences that do occur are detailed in descriptions of individual rock types or plutons.

Commonly, more than half the rock volume in the intrusions consists of plagioclase. It occurs as seriate 

euhedral to anhedral grains reaching maximum lengths 

of about 6 mm in some rocks but not more than 1 mm in 

many. In general, plagioclase was the earliest mineral to 

crystallize and grains tend to larger sizes than other 

mineral grains. Nearly all grains show albite twinning, 

but twinning according to other laws, particularly 

Carlsbad and pericline, is common. Many crystals, particularly those in the smaller masses and dikes, have 

subparallel orientations indicative of flowage. Rounded 

and abraded grains resulting from protoclasis are common, particularly near contacts.

Nearly all plagioclase grains are zoned, and most of 

the larger ones show numerous oscillatory zones, but 

smaller grains commonly show only a few. In some of the 

finer grained rocks, only progressive zoning occurs. 

Oscillatory zoned crystals from some of the coarser 

grained rocks are surrounded by progressively zoned 

sodic rims of irregular and varying widths. The extreme 

range of composition of zoned crystals ranges from 

labradorite in the cores to sodic oligoclase in the rims; 

the average composition is generally medium andesine. 

In many of the younger rocks, the range of composition is 

fairly narrow and averages calcic oligoclase; cores are no 

more calcic than andesine. Plagioclase from most rocks, 

particularly the coarser grained ones, shows extensive 

patchy zoning.

Quartz occurs as anhedral grains as much as 2 mm 

across, as irregular, intricately interlocking aggregates, 

or interstitially. In rocks with protoclastic textures, interlocking aggregates also form anastomosing seams that 

wind about and wrap around abraided crystals of 

plagioclase. Larger individual grains are commonly 

broken and consist of mosaics whose elements are 

slightly rotated so that they do not extinguish 

simultaneously. Most grains, large or small, show undulatory extinction. Curved lines of minute inclusions of 

an unknown mineral or minerals cut across the larger 

grains; liquid inclusions are comparatively rare. Some 

quartz in rocks containing considerable potassium feldspar occurs as myrmekitic intergrowths with sodic 

plagioclase, mostly where such plagioclase is in contact 

with potassium feldspar.

Potassium feldspar is white and ranges in amount 

from 0 in some quartz diorite to as much as 35 percent in 

some quartz monzonite. All is invariably late and 

replaces other primary minerals, particularly plagioclase. It occurs as interstitial, irregular grains or as 

seams, and simultaneously extinguishing amoeboid
TERTIARY INTRUSIVE ROCKS 57

splotches as much as 5 mm across that contain partly 

resorbed crystals of biotite and plagioclase and, less 

commonly, quartz. In some rocks, however, potassium 

feldspar and late quartz appear to have crystallized 

simultaneously. Some of the protoclastically deformed 

rocks contain numerous anastomosing seams of potassium feldspar and quartz that envelope rounded and 

abraded crystals of plagioclase. Most of the potassium 

feldspar is perthitic, and grid twinning indicative of 

microcline is uncommon in all rocks and absent in most.

Biotite is the principal mafic mineral and occurs in 

varying amounts in all the rocks to a maximum content 

of about 20 percent. Most of it is shredlike, and euhedral 

plates are rare. Crystal faces parallel to the basal 

cleavage, however, are generally well preserved and show 

as straight edges in thin section, but faces normal to the 

cleavage are mostly frayed and highly irregular. Biotite 

grains in protoclastic rocks are mostly warped, but some 

biotite seems to have crystallized after protoclasis, and 

grains are undeformed and cut across zones of granulation. Biotite tends to replace hornblende in rocks containing both hornblende and biotite. Characteristically, 

pleochroism is generally extreme and ranges from light 

straw yellow in the X direction to nearly opaque dark 

muddy brown or very dark red in the Z direction. 

Although none of the mineral was chemically analyzed, 

the extreme pleochroism and high index of refraction 

(Ny = 1.66) indicate a high iron content.

Hornblende occurs in all the rocks except the generally 

fine grained biotite granodiorite and quartz monzonite, 

although it is not present in all thin sections of the other 

rock types. Normally, hornblende-bearing rocks contain 

less than 10 percent of the mineral, but a few contain as 

much as 20 percent. It occurs both as prismatic euhedral 

crystals and as ragged grains. Poikilitic inclusions of 

plagioclase and opaque minerals are numerous in many 

crystals, especially the anhedral, ragged ones. Most of 

the hornblende is pleochroic in light shades of yellowish 

green or green, but some ranges from light green to dark 

green or greenish brown. Some hornblende has been 

partly replaced by either biotite or light-colored aggregates of acicular actinolite.

Accessory minerals commonly seen in thin section are 

magnetite, ilmenite, titanite, apatite, allanite, and 

zircon. Magnetite and ilmenite occur in all the rocks as 

scattered, usually irregular small grains, but some ilmenite forms skeletal crystals. Titanite occurs sparingly 

as rhombs as much as 2 mm long or secondary finegrained aggregates replacing biotite. Many thin sections 

contain two or three grains of allanite, some of which are 

2 mm across; some allanite crystals are zoned, the colors 

ranging from reddish orange to brownish red. Apatite is 

fairly common, usually as small stubby prisms. Zircon is 

rare and is almost entirely confined to biotite, in which it 

produces pleochroic halos.

Secondary minerals are chlorite, clinozoisite-epidote, 

actinolite, titanite, and sericite. Of these, chlorite, 

largely negative penninite, is most abundant, commonly 

as an alteration product of biotite and much less so of 

hornblende. Small amounts of clinozoisite-epidote 

replace the more calcic varieties of plagioclase and occasionally hornblende, but the most common alteration 

product of hornblende is nearly colorless (in thin section) 

actinolite. A little sericite was seen in nearly all thin sections, most frequently in the more calcic parts of 

plagioclase crystals.

TEXTURES

Textures of the various late Eocene rocks differ considerably, not only from mass to mass but within a single 

mass. Textures of each of the units shown on the maps 

(Cater and Crowder, 1967; Cater and Wright, 1967) are 

sufficiently distinctive, however, to permit ready field 

identification. The rocks in the smaller masses are 

generally fine grained and some are porphyritic, whereas 

most of the rocks in the Duncan Hill, Railroad Creek, 

and Rampart Mountain plutons are medium grained. 

Grain sizes decrease toward the contacts of some masses, 

but more striking are the streaky and, in places, gneissic 

textures resulting from protoclasis near the margins of a 

few masses and almost throughout the constricted 

northern part of the Duncan Hill pluton.

Normally both fine- and medium-grained rocks are 

hypidiomorphic granular. Directive textures manifested 

by subparallel orientations of tabular crystals are common locally, especially in some of the finer grained rocks. 

Crystals in most of the rocks tend to be seriate, but some 

rocks are equigranular and a few are porphyritic. Grain 

sizes of fine-grained rocks are in the range of 0.1 to 1.0 

mm, and those of medium-grained rocks from 1 to 6 mm; 

phenocrysts of porphyritic varieties are generally 3 to 6 

mm across.

In porphyritic rocks, plagioclase, hornblende, and, less 

commonly, biotite form phenocrysts. The plagioclase is 

euhedral and is the same size and habit as the 

plagioclase in the medium-grained rocks, whereas the 

groundmass plagioclase is subhedral.

Protoclastic textures are common in the larger masses 

and in dikes of biotite granodiorite and quartz monzonite. Granulation ranges from that which is barely 

perceptible under the microscope to the streaked, 

pseudogneissic varieties particularly common in the 

Duncan Hill pluton where granulation is readily apparent to even the unaided eye. The microscope is 

generally needed, however, to discern the late-crystallized minerals that grew across zones of granulation.

Cataclastic modifications of primary textures are 

locally common; these grade into mylonite along fault 

zones.
58 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

ANALYTICAL DATA

The compositions of the various upper Eocene intrusive rocks in the area were determined by 18 complete 

rock analyses using flame-photometric, atomicabsorption, and colorimetric methods for the major oxides. Nine of these were composite samples consisting of 

numerous chips of representative specimens of given 

rock types; the others are of single specimens of typical 

rocks in the various plutons, or of different facies within 

the Duncan Hill pluton. The minor elements were determined by semi quantitative spectrographic analyses. The 

analyses and calculated CIPW norms are given in the 

various accompanying tables and plotted on triangular 

diagrams. As might be expected, plots of the finer 

grained rocks show less scatter than do those of the 

coarser grained rocks.

DESCRIPTION OF ROCKS

The various plutons are described in order of known or 

inferred decreasing age. Only the Larch Lakes and Rampart Mountain plutons are isolated, and so far as is 

known, they are only in contact with each other and 

some dikes, but their general similarity to other upper 

Eocene rocks and their relation to certain dikes strongly 

suggest they are of the same general age, although no 

radiometric age determinations have been made. 

Because the order of emplacement of the rocks, where 

the order is known, is generally the order of increasing 

silica and alkali content, the Rampart Mountain pluton 

is presumed to be slightly younger than the Larch Lakes 

pluton because it contains more of these constituents. As 

is explained later, however, the increase in silica and 

alkalis may be more nearly related, at least for some 

plutons, to the position of a rock in the pluton rather 

than to its position in an emplacement sequence; this is 

more specifically true of the Duncan Hill pluton.

DIKES

Dikes, in many places closely grouped in swarms, are 

particularly numerous east of the Chiwawa River. Some 

of those designated on the geologic quadrangle maps 

without a symbol for geologic system are probably older 

than late Eocene, and those that have undergone 

regional metamorphism are unquestionably older and 

are, in fact, the oldest intrusive rocks in the mapped 

area. Such dikes, however, are rare. In areas where dikes 

are numerous, only a small percentage are shown on the 

maps, but these are selected to show the prevailing strike 

and distribution. Where little doubt existed concerning 

the affinities of late Eocene dikes, they were given appropriate letter symbols such as those given to the 

Railroad Creek pluton, but many of the dikes could not 

be assigned with confidence to any of the larger intrusive

masses. Most dikes are less than 50 m thick, but a few 

are as much as 60 m or more thick.

The dikes consist of a rather wide variety of types; the 

aphanitic types designated on the geologic quadrangle 

maps are particularly diverse. Many that appear nearly 

identical megascopically differ greatly in composition, 

and, conversely, many that appear to be different in outcrop appearance are seen to be of similar composition 

when viewed under the microscope. Spessartite, 

hornblende-quartz diabase or pawdite, porphyritic 

diabase, augite minette, and kersantite have been identified. Nonporphyritic granitoid dikes designated on the 

maps consist of biotite-quartz monzonite and granodiorite, hornblende-biotite granodiorite and quartz diorite, 

and a few consist of alaskite.

PAWDITE

Probably commonest of the dark, fine-grained rocks is 

biotite-hornblende-quartz rock, called pawdite by 

Johannsen (1937, p. 319). From the Chiwaukum graben 

eastward, except for the northeast part of the Holden 

quadrangle, most of the dark, fine-grained dikes are 

pawdite, and they are particularly numerous in and 

around the south end of the Duncan Hill pluton. None, 

however, were seen to cut the Railroad Creek pluton. 

Throughout this area, most of the dikes strike northeast, 

but in the highly sheared contact zone bordering the Entiat pluton, east of Garland Peak and Rampart Mountain, swarms of pawdite and rhyodacite dikes strike 

north-northwest. In the area near the east edge of the 

Holden quadrangle west of Larch Lakes, the Larch 

Lakes pluton invades and forms a sort of migmatite with 

fine- to medium-grained pawdite; the pluton in turn is 

cut by dikes of spessartite that have chilled margins 

against the granodiorite of the pluton, showing thereby a 

considerable time lapse between the intrusion of pawdite 

and spessartite, despite their similarity of appearance. 

Most of the dikes are only a few meters thick, but a few 

are as thick as 8 m. The thinner dikes are aphanitic or 

very fine grained throughout, but the thicker dikes commonly grade from chilled margins of aphantic rock to 

central parts that approach medium grain.

Pawdite ranges from medium-gray, even-granular, 

fine-grained rocks having a salt and pepper appearance 

to those that are nearly black and almost aphanitic. 

Many are porphyritic, having conspicuous blades of 

shiny black hornblende in a fine-grained or aphanitic 

groundmass; this is particularly true of the dikes within 

the Chiwaukum graben and of the sills cutting conglomerate of the Swauk Formation west of the Chiwawa 

River; in these sills shiny black hornblende blades occur 

in a greenish gray aphanitic groundmass. The finer 

grained groundmass and the difference in appearance 

between the pawdite of dikes and sills in the graben and
TERTIARY INTRUSIVE ROCKS 59

those outside it are thought to be due to emplacement at 

shallower depths. Pawdite contains plagioclase, 

hornblende, and quartz as essential minerals in all the 

dikes and biotite in most of them; rather abundant 

magnetite, titanite, and apatite are accessory. Chlorite, 

actinolite-tremolite, epidote, sericite, and calcite are 

secondary. The average composition of plagioclase 

ranges from calcic andesine to bytownite, but in all thin 

sections examined the mineral is characterized by extreme zoning, commonly ranging from bytownite cores to 

albite rims. Hornblende occurs as anhedral to euhedral 

crystals pleochroic in various shades of brown, but in 

some sections the brown hornblende grades outward into 

green and from green into nearly colorless rims. Biotite, 

usually as shredlike grains, may occur in amounts of as 

much as 10 percent in some dikes, but in a few it appears 

to be absent. Quartz, commonly not more than about 5 

percent, occurs in all the dikes as interstitial grains and 

in a few as rounded, resorbed phenocrysts, which are surrounded by halos of green hornblende crystals. The 

degree of alteration varies considerably; some rocks are 

almost entirely fresh, whereas others are so badly altered 

that almost none of the primary minerals remain. Textures also are variable, ranging from hypidiomorphic to 

xenomorphic and porphyritic.

The diaschistic dikes and irregular masses of pawdite 

in and satellitic to the southern end of the Duncan Hill 

pluton strongly suggest that all the pawdite is related to 

that pluton.

KERSANTITE

Kersantite differs megascopically from the finer 

grained varieties of pawdite and some spessartite only in 

the presence of a few small, visible phenocrysts of 

biotite. The dikes are probably rare, although because of 

their close resemblance to other types of dikes, they may 

be more common than was suspected during the course 

of field mapping. Kersantite is a dark-gray, somewhat 

porphyritic rock, in which small phenocrysts (as much as 

1 mm long) of plagioclase and scarce flakes of biotite can 

be detected in a very fine grained groundmass. The rock 

consists mostly of calcic andesine and biotite and minor 

amounts of hornblende and less than 1 percent augite 

and quartz. The phenocrysts of andesine are euhedral 

and show both oscillatory and patchy zoning; the scattered phenocrysts of biotite have partly recrystallized 

around their margins to a felted mass of lighter colored 

biotite and a little magnetite. Scattered grains of partly 

resorbed quartz are surrounded by coronas of tiny green 

hornblende needles; these quartz grains may be 

xenocrysts. The groundmass consists of a mat of small 

andesine laths and shreddy flakes of biotite showing a 

trachytic texture.

AUGITE MINETTE

In the northeastern part of the Lucerne quadrangle are 

a number of very dark greenish gray dikes of minette. 

Most of these strike northeast as do most other dikes, 

but one was seen that had a northwesterly trend. Some 

are very fine grained, and only phenocrysts of biotite are 

visible, but others are medium grained, and biotite, feldspar, and light-green augite are visible. Some grade into 

pegmatitic facies containing biotite and orthoclase 

crystals as much as 2 cm across; miarolitic cavities are 

numerous. Microscopic examination showed the dikes to 

consist largely of biotite, orthoclase, microcline, augite, 

unusual amounts of accessory titanite, magnetite, and 

apatite, and a few grains of hornblende. Sericite, 

epidote, and calcite are secondary. Much of the feldspar 

is perthitic; cores of biotite crystals are considerably 

lighter in color than are the marginal parts. The texture 

is striking; euhedral crystals of the mafic minerals are 

enclosed in an anhedral mass of feldspar grains.

SPESSARTITE

Dikes of spessartite are numerous in two areas, in the 

southwest part of the Lucerne quadrangle and in the 

Holden mine area. The spessartites in the two areas differ somewhat in both appearance and composition. 

Those from the Holden area are uniformly very fine 

grained and nonporphyritic, whereas those from the 

Lucerne quadrangle are more variable and range from 

nearly aphanitic to medium fine grained, and many are 

porphyritic. Both range from dark greenish gray to 

nearly black. The Holden mine spessartite consists 

mostly of brown hornblende and albite in roughly equal 

proportions but contains, in addition, accessory quartz, 

apatite, magnetite, titanite, and, in a few sections, a little primary orthoclase. Biotite is absent. Secondary 

minerals are sericite, calcite, epidote, chlorite, orthoclase, and sulfides. Textures approach panidiormorphic. 

A few of these dikes are crowded with light-green ovoids 

as much as 1 cm across that consist of more or less 

radiate masses of albite laths and some epidote; a few of 

the ovoids have cores of quartz or epidote. Around these 

ovoid bodies, hornblende blades are packed as though 

forced out of the ovoids. Where the dikes cut the Holden 

ore body, they contain more numerous grains of sulfides, 

mostly pyrite, that are commonly associated with 

replacement splotches of chlorite. Some of the 

relationships of the dikes to the ore body, such as an 

enrichment in sulfides, suggest that the dikes were intruded during the end stages of the epoch of sulfide 

mineralization. On the other hand, dikes of biotitequartz monzonite and granodiorite that cut the ore are 

unquestionably younger, are unaltered, and contain inclusions of mineralized rock and sulfides. These siliceous 

dikes are, in turn, cut by spessartite and, hence, are
60 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

older than spessartite; furthermore, some of the spessartite dikes have chilled margins against ore. The increased abundance of sulfides where spessartite cuts ore 

is probably the result of picking up or assimilating some 

sulfides during the course of intrusion as did biotitequartz monzonite and granodiorite.

The spessartite dikes in the southwestern part of the 

Lucerne quadrangle also consist largely of plagioclase 

and hornblende, but the plagioclase is oligoclase rather 

than albite, and a few of the dikes also contain a little 

biotite. All dikes contain a small amount of quartz and 

magnetite and some have interstitial accessory 

orthoclase, but as compared with the Holden spessartites, apatite and titanite are rare. The usual secondary 

minerals sericite, chlorite, epidote, calcite, and 

pyrite occur in varying amounts. Many of the dikes 

have phenocrysts of hornblende as long as 5 mm. Some 

dikes are notably miarolytic, and most of the miarolytic 

cavities are surrounded by bleached zones from a fraction of a millimeter to 3 mm thick in which the 

hornblende has altered to chlorite, but oligoclase is unaltered. Otherwise, textures are similar to those of the 

Holden spessartites.

The relationship, if any, between the two types of 

spessartite dikes is not known. Both types cut other late 

Eocene intrusions and seem to be among the youngest of 

dikes, although none cut either the Old Gib volcanic 

neck (late Eocene) or the early Miocene Cloudy Pass 

batholith and related rocks. However, because of the 

close spacial relation between these dikes and other late 

Eocene rocks, they are believed to be related to them.

OTHER FINE-GRAINED, DARK DIKES

Sparsely scattered over the area are dark, fine-grained 

rocks having the composition of diabase or diorite. They 

consist of varying proportions of andesine or labradorite 

and hornblende, but a few contain a little clinopyroxene. 

Some appear to be similar to the diabase and finegrained diorite that characterize the contact complexes 

bordering various plutons, but the affinities of others are 

unknown. Most have not been affected by regional 

metamorphism, but a few have been recrystallized to 

form amphibolite dikes.

HORNBLENDE DIORITE OF UPPER ROCK CREEK

In the upper part of the Rock Creek watershed and adjacent areas are dikes of hornblende diorite that rather 

closely resemble the pawdite dikes and may, in fact, be 

related to them. These dikes range from perhaps 20 cm 

thick to one nearly 1.6 km long and 100 to 130 m thick; 

many are highly irregular and have amoeboid shapes. 

The rocks in the larger masses range from black and very 

fine grained in the chilled margins to mesocratic and

relatively coarse grained in the central parts where 

euhedral hornblende needles are as long as 7 mm. The 

thinner masses are dark and fine grained throughout. In 

the larger masses, coarser grained rocks of the central 

parts of the dikes have intruded the chilled border rocks 

and torn off fragments of them.

The hornblende diorite consists mostly of hornblende 

and andesine with 2 to 3 percent biotite and a little accessory quartz, orthoclase, and apatite. Sericite, 

chlorite, and actinolite are secondary. Hornblende, the 

most abundant mineral, is euhedral and brown, but in 

the coarser grained varieties it is zoned, the borders of 

many crystals ranging from light green to nearly 

colorless. Unlike the otherwise rather similar pawdite 

dikes, the average composition of the plagioclase is 

andesine, and the compositional range of the normally 

zoned crystals is narrower, ranging from calcic andesine 

to oligoclase. Quartz occurs either interstitially or as 

myrmekitic intergrowths with oligoclase. A very small 

amount of late orthoclase locally replaces plagioclase or 

forms granophyric intergrowths with quartz.

GRANITOID DIKES

Scattered through the area are numerous, rather lightcolored, generally nonporphyritic, fine- to rather coarsegrained dikes of granitoid textures. The dikes range in 

composition from alaskite to quartz diorite, but most are 

quartz monzonite and granodiorite. Some of the dikes 

are clearly related to various larger plutons; thus, dikes 

designated as granitoid rocks in the southeast part of the 

Glacier Peak and adjacent parts of the Holden 

quadrangles are probably satellitic to the Tenpeak 

pluton. Others possess mineralogic and textural 

characteristics that relate them broadly to late Eocene 

plutons, but many that cut the metamorphic rocks, 

although unaffected by metamorphism, have no clear affinities. In general, none of the granitoid dikes have 

chilled borders, although some of those believed to be of 

late Eocene age are finer grained near their margins. On 

the other hand, many contain patchy-zoned plagioclase 

suggestive of transport through a considerable range of 

temperature-pressure conditions. Most of the gneissic 

dikes that might thereby suggest a premetamorphic age 

are seen under the microscope to have protoclastic rather 

than crystalloblastic or metamorphic textures and, 

hence, were intruded following regional metamorphism.

The dikes consist of varying proportions of andesine or 

oligoclase, quartz, potassium feldspar, and biotite. 

Hornblende occurs in many but nearly everywhere in 

lesser quantities than biotite. Most show only minor alteration to sericite, chlorite, and epidote, but in a few, 

relatively little of the original components remain.
TERTIARY INTRUSIVE ROCKS 61

DUNCAN HILL PLUTON

The Dune an Hill pluton, the oldest, probably the 

largest, and certainly the most intriguing of the late 

Eocene intrusions in the general area differs markedly in 

a number of respects from the other Tertiary plutons 

and, for this reason, was investigated in reconnaissance 

beyond the mapped quadrangles. The pluton has a 

length of about 48 km, extending from Buckskin Mountain in the Holden quadrangle to Stormy Mountain 

about 23 km southeast of the Lucerne quadrangle. It is 

tadpole shaped and tapers from a width of about 9.6 km 

at its so-called head on Stormy Mountain to a width of a 

little more than 1 km at its so-called tail on Buckskin 

Mountain. The outcrop area is about 260 km2 .

The Duncan Hill pluton rather closely parallels the 

northwesterly trend of its host rocks, as do the older 

plutons in the area, but it cuts across them downdip. 

The north half of the pluton intrudes the west limb of a 

southeast-plunging antiform of upper Paleozoic 

metamorphic rocks. Southward, the relation of the 

pluton to host rocks is less clear because exposures are 

poor and the structure of the host rocks is less well 

known. Unlike other plutons in the area, the Duncan 

Hill pluton not only is compositionally zoned along its 

length the rocks grading from hornblende-quartz 

diorite in the northern part to rocks as silicic as rhyolite 

porphyry at the south end on Stormy Mountain but it 

also exposes rocks ranging in depth zones from 

mesozonal in the northern part to hypabyssal in the 

southern. In a few places and most conspicuously in the 

vicinity of Fern Lake, the rock consists of intrusive complexes and marble-cake mixtures of hornblende-biotitequartz diorite and granodiorite (fig. 72).

The great vertical range of exposure in the pluton is 

the result of differential uplift since intrusion. The 

north-trending northern Cascade Range uplift transects 

the northwest-trending pluton, and the north end of the 

pluton nearer the center of the uplift, where uplift was 

greatest, is much more deeply eroded than the south end 

on the east flank, where uplift and depth of erosion are 

only moderate. The amount of tilting since the Miocene 

is evident locally from the dip of Miocene basalt flows 

that cap some of the ridges near the southeast end of the 

mass, and much, possibly more, uplift occurred between 

intrusion of the pluton and extrusion of basalt. Some of 

the discussion of the shallow southeast end of the pluton 

is based on unpublished information contributed by C. 

A. Hopson of the University of California, Santa Barbara, to whom I am particularly indebted.

The contact relations of the pluton to its host rocks 

differ radically along its length. The northwest part of 

the pluton is mantled by a complex similar to those associated with many of the older plutons and consists of 

hornblendite, hornblende gabbro, diorite, quartz diorite,

FIGURE 72. Marble-cake mixture of biotite-quartz diorite and 

granodiorite in Duncan Hill pluton at Fern Lake, Lucerne 

quadrangle.

dikes of various compositions, and inclusions of host 

rocks. The complex is particularly thick and extends 

nearly 5 km beyond the discordant northwest end of the 

core of the pluton where intrusive material had an opportunity to insinuate itself along foliation planes of the 

metamorphic rocks. The complex thins southward on 

both sides of the core; on the southwest side it is 

traceable nearly to Cottonwood Guard Station, but on 

the northeast side, a mappable complex extends only to 

the North Fork of the Entiat River, although a few thin 

lenses occur as far south as South Pyramid Creek. South 

of where the contact complexes pinch out, the contact, 

where exposed, is generally fairly sharp; hornfels, 

migmatites, or thin granitized zones in the host rocks are 

at most only a few tens of meters thick. At the southern 

end of the pluton, for example, south of sample 42 (fig. 

76), the contact is almost knife sharp, and the pluton 

had a minimal effect on the host rocks.

Quartz diorite makes up nearly all the main body of 

the pluton north of Snow Brushy Creek and occurs 

sparingly throughout most of its length. North of Snow 

Brushy Creek, the rock is gray, medium grained, and 

somewhat gneissic (fig. 73). The pervasive gneissic or 

foliated fabric of the rock resulted from protoclasis and is 

strongest near the contacts; south of Snow Brushy 

Creek, where quartz diorite occurs sparingly, the rock is 

nonprotoclastic and, hence, nonfoliated.

Quartz diorite consists of andesine, quartz, biotite, 

and hornblende, but hornblende may be locally absent. 

Magnetite, ilmenite, titanite, apatite, allanite, zircon,
62 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

FIGURE 73. Protoclastic hornblende-biotite-quartz diorite near the 

north end of Duncan Hill pluton, Holden quadrangle.

and rare xenotime are accessory. Orthoclase occurs 

sparingly as tiny veinlets or as late replacements of 

plagioclase. Plagioclase shows both oscillatory and 

patchy zoning; cores are as calcic as An6o and rims as 

sodic as Ano. In a given thin-section slide, the average 

composition of crystals can range from An:i:! to An/tn. 

Hornblende is light yellowish brown in the X direction to 

green and brownish green in the Z direction; color in 

much of the hornblende is splotchy, and in some grains 

the rims tend to be greener. Biotite is pleochroic from 

yellow to reddish brown or nearly opaque muddy brown. 

Quartz forms irregular lenses and streaks of interlocking 

grains. Textures range from hypidiomorphic to 

thoroughly protoclastic; plagioclase and hornblende are 

commonly bent, broken, and abraded, but the later 

quartz and biotite are either undistorted or only slightly 

so. Modal composition of quartz diorite ranges from 45 to 

55 percent andesine, 10 to 35 percent quartz, 13 to 20 

percent biotite, and 0 to 15 percent hornblende; 

orthoclase, where present, rarely exceeds 1 percent 

(table 22). Southward the mafic minerals, particularly 

hornblende, decrease irregularly and potassium feldspar, 

mostly perthite, increases.

The bulk of the Duncan Hill pluton consists of either 

granodiorite or quartz monzonite, but of the two rocks, 

granodiorite is considerably more abundant. Although

granodiorite occurs sparingly north of Snow Brushy 

Creek, the creek's drainage basin roughly marks the 

transitional zone from quartz diorite to granodiorite. 

Within this zone, a distinction between quartz diorite 

and granodiorite for much of the rock would be impossible except in thin section, but, in general, rocks containing visible hornblende are likely to be quartz diorite. 

Granodiorite and quartz monzonite are light-colored, 

massive, medium-grained rocks in which books of 

euhedral biotite are conspicuous (fig. 74). Both consist of 

oligoclase or andesine, quartz, orthoclase or perthite, 

biotite, and locally a little hornblende. Titanite, opaque 

minerals, allanite, a little zircon, and, rarely, muscovite 

are accessory. Alteration products are saussurite and 

chlorite, but neither are abundant. Plagioclase shows 

both oscillatory and patchy zoning; oscillatory zones in a 

single grain are numerous and range in composition from 

Anio to Anr,r,; larger grains have thick, progressively 

zoned rims of sodic oligoclase. The average composition 

ranges from medium oligoclase to medium andesine, but 

rocks containing andesine are much more abundant. 

Some orthoclase is not visibly perthitic, but most of it is. 

Potassium feldspar is late and mostly replaces 

plagioclase; in some thin sections the potassium feldspar 

forms a mesostasis that extinguishes simultaneously 

over wide areas. Quartz mostly forms irregular interstitial grains or splotches that have replaced earlier 

formed minerals. Biotite and hornblende differ little 

from that in quartz diorite except that biotite in nonprotoclastic rocks is mostly euhedral. Modal compositions range between wide limits, but in granodiorite, 

plagioclase usually constitutes about half the rock, 

quartz about one-quarter, and potassium feldspar, 

biotite, and hornblende in varying proportions make up 

the rest. In quartz monzonite, plagioclase, quartz, and 

potassium feldspar occur in roughly equal proportions; 

biotite is present in amounts ranging between 5 and 15 

percent, and hornblende is absent.

Textures of granodiorite and quartz monzonite are 

typically hypidiomorphic, modified in places by minor 

protoclasis. Protoclastic textures are fairly common near 

the contacts as far south as Cottonwood Guard Station, 

but south of there they seem to be virtually absent. In 

the interior of the pluton, protoclastic textures occur 

sparingly as far south as Duncan Hill but no farther.

The hornblende-biotite-quartz diorite and granodiorite of intrusive complexes and marble-cake mixtures, such as those around Fern Lake (fig. 72), differ 

somewhat in outcrop appearance and in microscopic texture, but they are mineralogically practically identical. 

The quartz diorite is somewhat finer grained, darker, 

and slightly more foliate than the granodiorite, and in 

thin section a flow structure is indicated by a subparallel
TERTIARY INTRUSIVE ROCKS 63

TABLE 22. Modal analyses of samples of biotite- and hornblende- biotite-quartz diorite and granodiorite from the Duncan Hill pluton,

Holden and Lucerne quadrangles

[Leaders (---), unable to determine]

Sample

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

Plagioclase

50.1

50.9

46.2

55.1

64.1

46.7

53.3

21.9

55.1

58.6

65.9

47.9

59.2

52.2

50.6

42.7

54.1

52.5

61.2

62.3

39.9

51.7

49.1

47.2

62.2

50.7

41.0

53.1

48.6

62.3

61.9

39.2

41.9

33.5

52.3

43.8

36.1

33.2

24.9

24.7

29.8

25.7

Potassium 

feldspar

1.1

.5

4.1

0

.2

.7

.7

32.8

0

0

0

3.6

.2

7.6

3.1

9.1

.9

8.0

1.6

1.7

15.6

4.8

9.2

14.7

.1

11.1

13.7

4.6

14.5

.1

17.6

19.3

16.5

24.7

13.5

18.7

24.2

25.1

42.7

35.8

35.6

39.7

Quartz

34.0

25.2

35.4

29.3

15.1

19.8

31.4

38.9

8.7

17.1

11.3

7.9

13.8

25.1

32.6

41.8

24.5

26.0

19.1

16.2

21.4

21.1

25.1

21.8

15.7

30.6

36.3

30.1

28.1

15.7

13.4

28.7

31.8

31.1

21.4

19.6

23.5

26.5

28.8

34.1

29.7

30.2

Biotite

14.1

18.3

13.5

14.1

12.0

19.7

12.9

6.2

20.1

15.8

13.4

14.4

20.7

13.8

13.6

2.1

20.3

10.3

15.4

11.0

18.1

19.1

13.9

15.1

17.1

7.3

8.9

9.9

7.7

17.1

5.0

12.0

8.7

9.9

11.6

15.6

16.1

15.1

3.2

5.2

4.2

4.3

Hornblende

0

4.6

0

.1

7.3

11.3

1.5

0

15.3

8.3

8.2

23.3

5.5

0

0

0

0

3.0

1.1

7.9

3.9

3.0

2.3

0

4.4

.1

0

.8

.3

4.4

1.0

0

.7

.5

.5

1.6

0

0

.1

0

0

0

Accessory 

and secondary minerals

0.7

.5

.8

1.4

1.3

1.8

1.4

.2

.8

.2

1.2

2.9

.6

1.3

.1

4.3

.2

.2

1.6

.9

1.1

.3

.4

1.2

.5

.2

.2

.5

.8

.4

1.1

.8

.4

.3

.7

.7

.1

.1

.3

.2

.7

.1

Total 

mafic 

minerals

14.8

23.4

14.3

15.6

20.6

0

14.8

6.5

36.2

24.3

22.8

50.6

26.8

15.1

13.7

6.4

20.5

13.5

18.1

19.8

23.1

22.4

16.6

16.3

22.0

7.6

9.1

11.2

8.8

21.9

7.1

12.8

9.8

10.7

12.8

17.9

16.2

15.2

3.6

5.4

4.9

4.4

Anorthite in 

plagioclase crystals (percent)

Average

40

43

40

38

28

40

40

...

43

38

37

37

35

35

35

28

36

39

37

37

38

37

35

37

37

33

32

36

28

37

36

32

31

33

40

33

32

33

24

25

19

15

Core

45

48

45

44

38

61

...

...

50

...

51

...

45

...

63

57

...

39

37

39

40

54

50

44

52

44

55

48

33

27

25

29

Rim

30

28

28

31

21

27

...

...

27

...

...

...

27

...

20

...

22

15

...

20

18

20

...

19

17

19

15

18

13

15

15

8

16

7

7

Remarks

Protoclastic.

Do.

Do.

Do.

Do.

Do.

Porphyroclastic.

Hypidiomorphic; some

slight mortar texture.

Hypidiomorphic.

Hypidiomorphic ;

slight granulation.

Protoclastic.

1.9 percent sphene.

Near contact;

moderately protoclastic.

Do.

Do.

Do.

Hypidiomorphic.

Slightly protoclastic.

Rather fine-grained;

hypidiomorphic.

Hypidiomorphic.

Somewhat protoclastic.

Rather fine grained;

subparallel plagioclase crystals.

Hypidiomorphic.

Near contact;

somewhat protoclastic.

Seriate; hypidiomorphic.

Hypidiomorphic.

Do.

Do.

Do.

Hypidiomorphic; seriate.

Hypidiomorphic.

Coarse grained; hypidiomorphic.

Hypidiomorphic.

Do.

Do.

0.2 percent allanite;

hypidiomorphic.

Hypidiomorphic .

Hypidiomorphic-porphyritic.

Contains mordenite

veinlets.

Plagioclase, progressively

zoned; hypidiomorphic -

miarolytic.

Xenomorphic;

progressively zoned plagioclase.

Calcic cores of

plagioclase sericitized.
64 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

FIGURE 74. Biotite granodiorite from the Duncan Hill pluton at south 

edge of the Lucerne quadrangle.

arrangement of andesine laths. The granodiorite contains a little more perthitic orthoclase than the quartz 

diorite, and both differ from the normal granodiorite of 

the general area in that the biotite is shredlike rather 

than euhedral. Examination of thin sections confirms 

the impressions gained from examination of outcrops 

that the quartz diorite had not solidified when invaded 

by granodiorite. Many andesine crystals in both rocks 

are bent, broken, and abraded, but the perthitic 

orthoclase that partly replaces andesine in both rocks is 

undeformed. The intrusive complexes are probably 

slightly younger than the main mass of granodiorite in 

this part of the pluton inasmuch as inclusions typical of 

the main mass containing euhedral books of biotite are 

common. These inclusions are rounded and have blurred 

borders but otherwise show no effects from immersion in 

magmas of the complex. No intrusive contacts between 

the complexes and the main mass of granodiorite were 

observed.

Near the south end of the pluton surrounding and 

below Stormy Mountain, the rocks are miarolytic 

biotite-quartz monzonite and granite (fig. 75) that grade 

upwards into quartz latite and rhyolite porphyry and 

downward and northward into granodiorite and quartz 

monzonite. These gradations are gradual, and except for 

later dikes, no intrusive or abrupt contacts between rock 

types exist. Above an altitude of about 1,450 m on 

Stormy Mountain, the rocks are miarolytic, some of

FIGURE 75. Miarolytic biotite-quartz monzonite from the Duncan 

Hill pluton on Stormy Mountain, central Washington.

them strikingly so, for they contain almost 10 percent 

voids; below this altitude, the rocks are nonmiarolytic.

The miarolytic quartz monzonite and granite vary 

considerably in appearance; the rocks lower down are 

light colored, massive, medium grained, and contain 

books of euhedral biotite so characteristic of the 

granodiorite and quartz monzonite that make up the 

bulk of the pluton. Higher up the slopes of Stormy 

Mountain, the rocks become increasingly porphyritic 

and finer grained. In thin section, the textural differences are greater than are differences in outcrop appearance, although compositions are fairly uniform. 

Above an altitude of about 1,700 m on the southwest 

spur of Stormy Mountain, the rocks are conspicuously 

granophyric; below that altitude, the textures more 

nearly resemble those of normal granodiorite and quartz 

monzonite. The granophyric rocks tend to be more 

porphyritic and the nongranophyric rocks more 

granitoid. Chemically and mineralogically, they are virtually identical (sample 8, granophyre, and samples 10 

and 11, quartz monzonite, table 23).

A vast array of dikes and irregular masses of biotitehornblende-quartz diorite, lamprophyres, pawdite, and 

aplite characterize the south end of the pluton, particularly near the contacts and as satellitic dikes extending far out into the host rocks. The granophyric core 

rocks are somewhat later than the dark rocks and cut 

them in most places. Both composition and texture are 

highly variable.

All the rocks at higher altitudes in the vicinity of 

Stormy Mountain, except for the dikes, consist of 

perthite, quartz, oligoclase, a little biotite, and very 

rarely hornblende. In outcrop, it is impossible to distinguish between rocks having the composition of quartz 

monzonite and those of granite. All the feldspar, except 

the exsolved albite in the perthite, is clouded with 

numerous, highly birefringent, unresolvable inclusions. 

Generally the clouding is of uniform intensity through-
TERTIARY INTRUSIVE ROCKS 65

out the feldspars, and most of the minute inclusions are 

oriented along crystal directions of the feldspar. The 

oligoclase only rarely shows any zoning except progressive. A few oligoclase crystals have cores that have been 

saussuritized, and for a few where it was possible to 

determine the composition those cores are sodic 

labradorite, but for most crystals, the composition 

ranges between An3 3 in the core and An8 on the rims; the 

average composition is about An24 . Biotite is partly 

altered to opaque minerals, and much of it greenish or 

mottled in brown and green colors. Some of the 

miarolytic cavities are partly filled with mordenite. The 

pervasive cloudy feldspars and partly altered biotite 

strongly suggest much deuteric activity, perhaps associated with degassing of the pluton.

The intricate intermixture of diverse igneous rocks, 

hornfels, and varied inclusions forming the contact complex around the north end of the pluton is probably best 

described as an agmatite. The igneous rocks in this 

agmatite are mostly either hornblende gabbro or quartz 

diorite, but intermediate varieties exist. The gabbroic 

parts of the complex are commonly sharply bordered, irregular masses, but the more granitic rocks may have 

either sharp or gradational contacts with any of the other 

rocks. Much of the igneous part of the complex, particularly the more felsic rocks, shows a pronounced 

streakiness resulting from strong protoclasis. Inclusions 

in the complex range from sharply bordered angular 

fragments of metamorphic rocks showing little effect 

from their sojourn in the igneous material to shadowy, 

rounded xenoliths with gradational borders. Many inclusions consist of slightly older igneous rocks in dikes of 

younger ones. Common also are masses of coarse-grained 

hornblendite as much as several meters across; these are 

commonly veined and seamed by dikelets of gabbro, 

diorite, or quartz diorite.

Although age sequences of various igneous rocks in an 

outcrop may be consistent, different sequences may occur in another outcrop, indicating that the rocks were for 

the most part nearly simultaneous injections, an impression that is heightened by the marble-cake mixtures of 

rocks in some outcrops. Much of the rock in the complex 

closely resembles rocks in nearby plutons, some of which 

are older and some younger than the Duncan Hill. Thus, 

some of the gabbro in the complex is practically identical 

to the nearby and older hornblende gabbro of the Riddle 

Peaks pluton. The small amounts of granodiorite and 

quartz monzonite in the complex apparently are later 

and closely resemble some of the post-Duncan Hill rocks 

in the area; however, the quartz diorite is probably from 

the Duncan Hill.

Most of the rocks in the contact complex are fairly 

fresh, although locally plagioclase is partly saussuritized, and mafic minerals are altered to chlorite. Uncontaminated hornblende gabbro consists of roughly

equal proportions of plagioclase and hornblende with accessory opaque minerals and apatite. Plagioclase shows 

both oscillatory and patchy zoning, the zones ranging 

from rims as sodic as An^ to cores as calcic as Ans$; the 

average composition ranges between calcic labradorite 

and sodic bytownite. Textures are either xenomorphic 

or hypidiomorphic; protoclastic modifications are 

common.

Quartz diorite in the contact complexes differs 

somewhat from most of the quartz diorite of the core but 

consists of plagioclase, quartz, biotite, and, in some 

places, hornblende as essential minerals. Opaque 

minerals, titanite, apatite, and a little allanite are accessory. Plagioclase is andesine, much of it showing both oscillatory and patchy zoning; zones range from about An2 5 

on rims to An55 in some cores. Quartz may constitute as 

much as 25 percent of some of the rock and occurs either 

as a replacement of earlier formed minerals or as irregular folia, consisting of mosaics of interlocking grains. 

Textures range from hypidiomorphic to highly protoclastic; the decidedly protoclastic rocks are either 

streaky or strongly foliate. Seams of orthoclase are common in much of the quartz diorite and occur in some of 

the gabbro. Hybrid rock consisting of intricate mixtures 

of both gabbro and quartz diorite contain all the 

minerals common to the parent species; most striking is 

the occurrence of both bytownite and andesine in a 

single thin section in addition to plagioclase intermediate to these two extremes. Where not abraded by 

protoclasis, sodic rims on calcic plagioclase tend to be 

thicker in hybrid rock than in uncontaminated gabbro. 

All the hornblende, whether in gabbro, quartz diorite, 

hybrid rocks, or inclusions, is optically similar and is 

pleochroic in various shades of green. In some thin sections, the hornblende has been partly replaced by actinolite or biotite or both. Biotite is a late mineral in all 

the rocks, and even in some of the highly protoclastic 

varieties commonly shows little of the distortion or 

grinding that is so prevalent in plagioclase and 

hornblende. Alteration to chlorite is common only 

locally and may be related to other later small intrusions 

in the area, satellitic dikes of which cut the Duncan Hill 

pluton.

Inclusions range from little-changed blocks of host 

rocks to vague schlieren that differ little from the enclosing gabbro or quartz diorite. Most striking, however, are 

masses of hornblendite that may be several meters 

across. The hornblendite is coarse grained; the crystals 

commonly attain a length of 3 cm or more. The origin of 

the hornblendite is in doubt. The hornblende is optically 

similar to hornblende in the enclosing igneous rocks, and 

perhaps the hornblendite is merely made over from 

hornblende gneiss and schist inclusions brought up from 

depth that had spent a long time immersed in the 

magmas.
66 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 23. Chemical and spectrographic analyses and norms of rocks from the Duncan Hill pluton, central Washington

[For samples 1, 2, 4, 5, and 7, SiO2 , A1 2O), CaO, and K2O determined by X-ray fluorescence; 

total Fe and MgO determined by atomic absorption; FeO determined volumetrically; Na2O 

determined by flame photometer; TiO2 determined by Tiron-colorimetric method; and PjO-, 

determined colorimetrioally. Analysts; Violet Merritt, G. T. Burrow, J. P. Cahill, G. D. 

Shipley, and J. S. Wahlberg. For samples 3 and 6, SiO2 and Al 2O t determined 

colorimetrically; Fe2O3 , MnO, Zn, MgO, and CaO determined by atomic absorption; Na2O 

and K2O determined by flame photometer; FeO determined volumetrically. Analysts: G. T.

Burrow, J. D. Mensik, Claude Huffman Jr., Wayne Mountjoy, and H. H. Lipp. For samples 

8-11, SiO2, Al2 Oi, Fe 2O,, CaO, and K2O determined by X-ray fluorescence; FeO and TiO2 

determined volumetrically; MgO and Na2O determined by atomic absorption; and P2 O, 

determined colorimetrically. Analysts: G. T. Burrow, Johnnie Gardner, and S. D. Shipley. 

Spectrographic analyses by H. G. Neiman, Barbara Tobin, and L. A. Bradley. N.d., not 

determined. Leaders (---), below sensitivity level]

..... i 2 3 4 5 6 7 8

9'

10 11

Chemical analyses (percent)

SiO2 -----------

M2 03 ------

Fe2 O3 ----------

FpO

MgO -----------

PaH

Na2 O-----------

K2 0------------

T;r»

P

/-\

MnO-----------

Zn -------------

Total-------

CT\ n

..... 1 Q7

A."\A.

o 90

c 7

A. 1Q

1 c

----- .95

on

----- N.d.

----- N.d.

----- 99

63.0 

15.9 

1.52 

4.40 

2.47 

5.5 

3.57 

2.0 

1.03 

.41 

0.15 

N.d.

100

63.0 

17.3 

.76 

4.45 

1.6 

5.2 

3.56 

2.13 

N.d. 

N.d. 

.36 

.009

99

66.4 

16.0 

.73 

3.06 

1.33 

3.6 

3.73 

2.8 

.64 

.24 

N.d. 

N.d.

99

68.3 70.0 

15.5 16.4 

.53 .49 

2.13 2.53 

1.13 0.81 

3.6 3.6 

3.90 3.86 

2.6 2.40 

.44 N.d. 

0.17 N.d. 

N.d. .055 

N.d. .006

98 100

72.0 

14.4 

.60 

1.86 

.97 

2.6 

3.67 

3.3 

.42 

.14 

.081 

N.d.

100

73.9 

13.9 

.71 

.80 

.16 

.90 

3.83 

5.3 

.12 

.08 

.02 

.004

100

74.2 

13.2 

1.11 

.62 

.09 

.7 

3.43 

5.6 

.12 

.08 

.05 

N.d.

99

75.4 

13.1 

.76 

.58 

.11 

.6 

3.30 

5.7 

.07 

.08 

N.d. 

N.d.

100

74.2 

12.8 

.52 

.52 

.08 

.8 

3.50 

5.5 

.06 

.08 

N.d. 

N.d.

98

Semiquantitative spectrographic analyses (parts per million)

Ra

Be -------------

Co -------------

Cr -------------

Cu-------------

La -------------

Nb-------------

Ni -------------

Pb-------------

Sc -------------

Sr -------------

V --------------

Y --------.--...

Zn -------------

rj

TP

fia

Li--------- -----

Yb-------------

Nd-------------

----- 700

----- 1.5

----- 15

OA

..... 7

----- 10

..... 7

----- 70

----- 15

700

100

1 ^

1 ^O

QA

----- 1.5

700 

1.5 

15 

30 

20 

50 

10 

7 

200 

15 

500 

100 

15

150 

30 

1.5

1,500

50 

50 

30

20

20 

700 

150 

15

70 

20 

2

1,500 

1.5 

7 

15 

10 

70 

10

20 

15 

500 

70 

15 

150 

150

20

1.5 

70

700 1,000

10 7 

30 15

7 5

7 10

150 70 

15 7 

500 500 

70 70 

15 10 

500 300 

30 70

15 15 

1.5 1.5

1,000

20 

30 

10

10

20 

700 

150 

15

70 

20 

2

1,000 

1.5

7 

15

7

10

70 

7 

300 

30 

15

150 

20 

2

700 

1.5

10 

3 

100

20 

50 

70 

10 

30

150 

200 

30 

50 

3

1,000 

1.5

5

20 

5 

70

15 

70

20 

50 

1.5

500 

1.5

7 

1

15 

70 

10 

70

20 

50 

1

Norms

q ..............

ah

ati

di--------------

hy - -. -

il ..............

fl Q1

qc 97

94. f\f\

----- 1.07

----- 10.13

----- 0

O 0.7

1 01

QQ

18.52 

11.82 

30.20 

21.46 

2.59 

10.27 

0 

2.21 

1.96 

.97

16.85 

12.73 

30.45 

25.22 

.73 

12.90 

0 

1.12 

0 

0

23.53 

16.79 

32.01 

16.53 

0 

7.38 

.88 

1.07 

1.23 

.58

25.96 27.44 

15.62 14.16 

33.55 32.59 

17.03 17.83 

0 0 

5.66 6.36 

.14 .91 

.78 .71 

.85 0 

.41 0

30.33 

19.49 

31.02 

11.97 

0 

4.79 

.40 

.87 

.80 

.33

29.18 

31.40 

32.48 

3.95 

0 

1.12 

.42 

1.03 

.23 

.19

31.63 

33.35 

29.24 

2.97 

0 

.34 

.42 

1.62 

.23 

.19

33.14 

33.78 

27.99 

2.46 

0 

.60 

.61 

1.11 

.13 

.19

31.60 

33.20 

30.24 

3.04 

.40 

.44 

0 

.77 

.12 

.19

Total ---------... innnn inn nn innnn mnnn innnn mnnn innnn mnnn innnn mono innnn
TERTIARY INTRUSIVE ROCKS 67 

TABLE 23. Chemical and spec trographic analyses and norms ofrocks from the Duncan Hill pluton, central Washington Continued

Sample 10 11

Plagioclase composition

41.0 41.6 45.3 34.1 33.7 35.4 27.9 10.8 9.2 8.1 9.2

Sample descriptions

1. Hornblende-biotite-quartz diorite; north of Cool Creek.

2. Composite sample of hornblende-biotite-quartz diorite; Borealis Ridge.

3. Composite sample of hornblende-biotite-quartz diorite; Snow Brushy Creek.

4. Biotite granodiorite; Fern Lake.

5. Biotite granodiorite; Duncan Hill.

6. Composite sample of biotite granodiorite; ridge north of Crow Creek.

7. Composite sample of biotite granodiorite; Shady Pass road froml.5 to 3 km south of Lucerne quadrangle.

8. Miarolytic biotite-quartz monzonite granophyre; about 2.5 km northeast of Stormy Mountain.

9. Miarolytic biotite-quartz monzonite; 1.25 km southeast of Stormy Mountian, altitude 1,900 m.

10. Biotite-quartz monzonite, slightly miarolytic; 3 km southwest of Stormy Mountain, altitude 1,600 m.

11. Biotite-quartz monzonite; 5 km southwest of Stormy Mountain, altitude 1,450 m.

The composition and zoning of plagioclase provides 

considerable information on the course of differentiation 

in the pluton and imposes certain restrictions on the possible processes of differentiation. The most notable compositional change that takes place in plagioclase is a 

progressive decrease in average anorthite content from 

north to south in the pluton. On the other hand, except 

for the hypabyssal rocks at the south end of the pluton, 

the range of composition of cores of individual crystals 

remains virtually the same throughout its length; 

southward, however, the rims of crystals become increasingly thick and sodic. The plagioclase in quartz 

diorite north of Snow Brushy Creek has an average composition of medium andesine, commonly between An38 

and An4o; the cores of larger crystals are sodic labradorite 

(An5o to Anss), but the rims are rar-ely more sodic than 

An3 3. Plagioclase from rocks south of Snow Brushy Creek 

is sodic andesine and ranges in composition from about 

An33 to An37 , becoming more sodic to the south. The rims 

are as sodic as Ani8 , but the cores are similar to those in 

the plagioclase from quartz diorite to the north. 

Plagioclase in the hypabyssal rocks in the Stormy Mountain area is oligoclase, having a composition of about 

An2 4j rims are as sodic as An?, and few cores are more 

calcic than An30.

Zoning of plagioclase crystals occurs in two contrasting styles, one confined to the hypabyssal rocks, the 

other to the rest of the pluton. Plagioclase in the hypabyssal rocks is progressively zoned; almost no crystals 

show either oscillatory or patchy zoning, and the rare 

ones that do are highly sericitized and show evidence of 

extensive resorbtion. Plagioclase from the remainder of 

the pluton typically shows both oscillatory and patchy

zoning. Plagioclase in granodiorite and quartz monzonite is mostly rimmed by progressively zoned 

oligoclase. The width of these progressively zoned rims 

increases southward along the length of the pluton. 

Andesine in quartz diorite north of Snow Brushy Creek 

has no such rims or very thin ones.

The lack of oscillatory and patchy-zoned plagioclase 

crystals in the hypabyssal rocks is in marked contrast to 

the plagioclase crystals in the hypabyssal rocks in the 

nearby Miocene Cloudy Pass batholith and points to 

some marked differences in the late histories of the two 

intrusions; these are discussed later in the section on 

"Composition and differentiation."

Modal analyses of rocks from the Duncan Hill pluton 

are given in table 22 and the sample locations are shown 

in figure 76; modes are plotted in figure 77. Chemical 

analyses and calculated norms for various rocks in and 

related to the Duncan Hill pluton are given in table 23, 

appear on the variation diagram of figure 78, and are 

plotted on a traingular diagram in figure 79. The variation diagram illustrates well two rather striking features 

of the pluton: first, the uniformity of composition of the 

quartz diorite at the north end and the hypabyssal rocks 

at the south end of the pluton, and second, the wide 

variability of the rocks in between. The progressive 

changes in composition that occur along the length of the 

Duncan Hill pluton, aside from a few minor exceptions 

such as the small intrusive complexes in the vicinity of 

Fern Lake, are almost imperceptibly gradational and 

almost certainly are a reflection of vertical rather than 

lateral zoning. The differentiation processes responsible 

for the compositional zoning are discussed later in the 

section on "Composition and differentiation."
68

120°45'

INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

120°30'

Biotite-hornblende-quartz diorite,

pawdite, lamprophyre, and aplite

of Duncan Hill pluton 

Quartz diorite, granodiorite, and

quartz monzonite of Duncan Hill

pluton 

Duncan Hill contact zone

Granodiorite of Larch Lakes pluton

Quartz monzonite of Rampart

Mountain plutons

Modally analyzed samples of 

tables 22, 24, and 26

Chemically analyzed samples of 

table 23. Circled number is 

sample number in table 23

FIGURE 76. Map showing location of chemically and modally analyzed samples of Duncan Hill, Larch Lakes, and Rampart Mountain

plutons, central Washington.

LARCH LAKES PLUTON

Cropping out in the Larch Lakes cirque and on the 

ridge to the west, Lucerne quadrangle, is the biotite 

granodiorite of the Larch Lakes pluton. The pluton, an 

irregular mass nearly 2 km across in greatest dimension, 

intrudes the Entiat pluton, but its absolute age and relation to other dated intrusions are not known. Its close 

resemblance to known late Eocene intrusions and the 

fact that it cuts pawdite dikes and is cut by types of 

dikes that cut the plutons dated as late Eocene but not 

the Miocene Cloudy Pass batholith indicates that it, too, 

is late Eocene. 

Rocks of the Larch Lakes pluton are light gray, usually
TERTIARY INTRUSIVE ROCKS 69

Quartz

Plagioclase

Potassium 

feldspar

FIGURE 77. Plot of modes of rock samples from the Duncan Hill 

pluton, central Washington, on a quartz-potassium feldsparplagioclase diagram. Sample analyses given in table 22.

fine grained, homogeneous, and massive, but locally 

they are medium grained (fig. 80). They range in composition from quartz diorite to quartz monzonite, but 

most are granodiorite. Some show a slight foliation 

because of the parallel orientation of biotite flakes, and 

locally vague clusters of biotite crystals define a faint 

lineation in the plane of the foliation. Wherever 

observed, contacts are sharp and commonly transect the 

foliation of the host rocks.

Thin-section examination shows rocks of the pluton to 

consist of vary ing proportions of andesine, quartz, potassium feldspar, and biotite as primary minerals, and 

titanite, apatite, and opaque minerals as accessory constituents. Chlorite, sericite, and clinozoisite-epidote are 

secondary. Textures are hypidiomorphic granular and 

tend toward subparallel arrangements of andesine laths 

in some thin sections. The subhedral to euhedral crystals 

of andesine are strongly zoned and many show both oscillatory and patchy zoning. The range of composition of 

various zones in some crystals is as great as Anis to An45 , 

but the average composition in the biotite-quartz monzonite is about An32 and in the quartz diorite is between 

Ans? and An4o. Quartz and potassium feldspar are interstitial; most of the potassium feldspar is slightly 

perthitic orthoclase but a little microcline was seen in 

one or two sections. Biotite occurs as reddish brown, 

highly pleochroic, anhedral shreds, much of it showing a 

rude alinement. Chlorite replaces a little of the biotite, 

and sericite and clinozoisite-epidote replace the

a.

E

CD 

CO

20, 

9,16

10

0

5

O

£

X

o

2 

CO

O

9,to 

Z

0

H

60

in to co^-

"5. "5. "5. "5. "5. "Q.'Q.'Q.

E EEEEEEE

CD CD CD CD CO CO CO CO

CO CO CO CO CO COCO CO

70 80

SiO2 , IN WEIGHT PERCENT

FIGURE 78. Variation diagram of major oxides in rock samples from 

the Duncan Hill pluton, central Washington.

andesine, but the amounts of these minerals are small as 

the rocks are largely unaltered.

Locations of modally analyzed specimens are shown in 

figure 76. Modal analyses (fig. 81; table 24) indicate that
70 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Quartz

Albite Potassium feldspar

FIGURE 79. Plot of norms of rock samples from the Duncan Hill 

pluton, central Washington, on a quartz-potassium feldsparplagioclase diagram. Sample analyses are given in table 23. Isobaric 

lines mark position of the quartz-feldspar boundary at various water 

pressures. Arrows show position of ternary eutectic.

FIGURE 80. Biotite granodiorite from the Larch Lakes pluton, 

Lucerne quadrangle.

the compositions of rocks in the Larch Lakes pluton occupy two distinct fields, one near the border between 

quartz diorite and granodiorite and the other near the 

middle of the quartz monzonite field. The chemical 

analyses (table 25) were made of specimens selected 

from the quartz diorite-granodiorite grouping. The differences between these rock types is scarcely apparent in 

hand specimen, and the two varieties were not 

separately mapped. A plot of the norms of the pluton is 

shown on figure 71.

The Larch Lakes pluton has removed and displaced its 

host rocks, which show no tendency toward being 

shouldered aside. The lack of inclusions or foundered 

blocks of host rocks in the pluton suggests that stoping 

was not particularly efficacious in providing space for 

the pluton.

RAMPART MOUNTAIN PLUTON

The Rampart Mountain pluton, cropping out between 

Rampart Mountain and Larch Lakes, is about 3 km long 

and about 1 km wide. It trends north-northwest more or 

less parallel to the trend of enclosing host rocks, cuts the 

Entiat pluton, and is in turn cut by porphyritic dikes. 

The north end of the pluton is in contact with the Larch 

Lakes pluton, but where observed it was impossible to 

determine which cut the other. The observed contact is 

gradational through a distance of 2 to 30 cm, and the 

faint foliation in both rocks is parallel to the contact. 

Neither rock includes fragments of the other, and the 

general appearance of the contact suggests that 

regardless of which was older, it was probably still partly 

molten when intruded by the younger.

The rocks in the Rampart Mountain pluton consist of 

light-gray, medium-grained, massive biotite granodiorite and quartz monzonite nearly identical to some of 

the more alkalic rocks of the Larch Lakes pluton (fig. 

82). Some of the rocks are vaguely foliated because of the 

alinement of biotite flakes. Most of the rock is 

probably quartz monzonite, but the differences between 

quartz monzonite and granodiorite are not detectable in

TABLE 24. Modal analyses of samples of granodiorite from the Larch Lakes pluton, central Washington

[Leaders (- - -), unable to determine]

Sample

No.

43

44

45

46

47

Plagioclase

46.0

36.5

46.4

53.1

36.3

Potassium 

feldspar

11.2

28.3

7.4

5.2

28.1

Quartz

32.4

27.0

32.1

27.2

29.1

Biotite

8.9

6.5

13.3

13.5

4.7

Accessory 

and secondary minerals

1.5

1.5

.8

1.0

.8

Total 

mafic 

minerals

10.4

8.0

14.1

14.5

5.5

Anorthite in 

plagioclase crystals (percent)

Average

40

32

40

37

40

Core

35

60

51

Rim

15

20

17

Remarks

Fine grained; hypidiomorphic.

Fine grained; hypidiomorphic.

Subparallel andesine

crystals; fine grained.

Fine grained; hypidiomorphic.

Subparallel andesine

crystals; fine grained.
TERTIARY INTRUSIVE ROCKS 71

TABLE 25. Chemical and spectrographic analyses and norms of a 

composite sample of biotite granodiorite from the Larch Lakes 

pluton, central Washington

[SiO> and Al>Oi determined colorimetrically; Fe2Oi, MgO, CaO, and MnO determined by 

atomic absorption, FeO determined volumetrically; NajO and K>O determined by flame 

photometer. Analysts: Wayne Mountjoy, J. D. Mensik, Claude Huffman, Jr., G. T. Burrow, 

H. H. Lipp. Spectrographic analyses by Barbara Tobin]

Chemical analyses 

(percent)

Si02 ----------69.5

A1 2 03 ----------16.7

Fe2 03 --------- .31

FeO ----------- 2 33

MgO ---------- .63

CaO ---------- 3.0

Na2 0---------- 3.96

KZ 0----------- 3.01

MnO---------- .06

Total ------- 100.00

Semiquantitative 

spectrographic 

analysis (parts per million)

Ba --------- 1,000

Co--------- 10

Pr 1^

Cu--------- 3

Ga--------- 20

Sc --------- 10

Sr --------- 700

V ---------- 70

Y---------- 15

Yb--------- 1.5

Zr --------- 70

Norms

q .............25.85

or.. ........ ...17.87

an 14 Q 1^

hy .---...----- 5.73

r - - - 1 4Q

mt 4^

Total ------ -100.00

an ------------30.8

outcrop. Contacts of the pluton with rocks other than the 

Larch Lakes pluton are sharp but irregular, and near the 

contact in some places, particularly on the west flank of 

Rampart Mountain, stoped blocks of host rocks are 

numerous and many dikes of biotite-quartz monzonite 

project short distances into the enclosing rocks.

The granodiorite and quartz monzonite of Rampart 

Mountain pluton consist of roughly equal amounts of 

oligoclase and quartz and more variable amounts of 

potassium feldspar. Biotite makes up 5 to 12 percent of 

the rock and muscovite 1 to 4 percent. Titanite, apatite, 

allanite, and magnetite are accessory. Epidote and 

sericite (some of the sericite is coarse enough to be called 

muscovite) replace both biotite and oligoclase, particularly the more calcic cores of oligoclase; chlorite and 

magnetite are alteration products of biotite.

Oligoclase is subhedral to anhedral, and shows oscillatory or progressive zoning and also patchy zoning. Some 

crystals are bordered by myrmekite where they are in 

contact with potassium feldspar. The oligoclase has an 

average composition of about An2 e; the extreme range of 

composition within zones of a single crystal are from 

Anir, on the rims to An:!2 in the cores, but commonly the 

range is only from about An2o to An2 8. Quartz is interstitial or forms aggregates of small, interlocking grains. 

The potassium feldspar is either interstitial or forms irregular grains 2 or 3 mm across that enclose partly 

resorbed oligoclase crystals. Potassium feldspar mostly 

shows the grid twinning of microcline, but some is untwinned and presumably is orthoclase. In some crystals, 

parts are twinned and the rest untwinned. Untwinned 

material, whether making up either a part of or an entire

Quartz

Piagioclase

Potassium 

feldspar

EXPLANATION 

 41 Larch Lakes pluton 

&45 Rampart Mountain pluton

FIGURE 81. Plot of modes of rock samples from the Larch Lakes and 

Rampart Mountain plutons, Holden and Lucerne quadrangles, on a 

quartz-potassium feldspar-plagioclase diagram. Sample analyses are 

given in tables 24 and 26.

FIGURE 82. Biotite-quartz monzonite from the Rampart Mountain 

pluton, Holden and Lucerne quadrangles.

crystal, is perthitic, whereas feldspar showing grid twinning is either nonperthitic or only slightly so. Biotite occurs as irregular, somewhat shreddy crystals that vary 

considerably in pleochroic characteristics; in some thin 

sections, the biotite is pleochroic in shades of brown, and 

in others, it is from light straw yellow to deep, almost
72 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

opaque muddy brown. The relatively abundant 

muscovite in these rocks is unique among the late 

Eocene intrusives. It ranges from fine-grained sericitic 

material that is obviously secondary to flakes 1 mm 

across, some of which may be primary.

Epidote occurs in two distinct forms, that which 

replaces oligoclase and forms irregular small grains or 

granular masses, and that associated with or replacing 

biotite, which forms rather large, euhedral crystals as 

much as 1 mm or more across. One crystal of allanite 

was seen that was mantled by a thick overgrowth of 

epidote in crystal continuity. Chlorite is mostly negative 

penninite.

Textures are hypidiomorphic and seriate. Some sections show a vague subparallel arrangement of oligoclase 

grains suggestive of flowage. A slight tendency to 

protoclasis is apparent in a few sections.

Modal analyses are shown in fig. 81 and table 26, and a 

chemical analysis of a composite of a number of chips of 

typical rock is shown in table 27.

The Rampart Mountain pluton mostly removed the 

intruded rock, but the south end of the pluton on the 

west flank of Rampart Mountain thrust aside the enclosing rocks to some degree, and the prevalance of stoped 

blocks of these rocks suggests stoping was also effective 

in making room for the pluton.

OLD GIB VOLCANIC ROCKS AND 

ASSOCIATED DACITE PORPHYRY

Old Gib volcanic rocks and associated dacite porphyry 

were formerly thought to be correlative with the 

petrographically and chemically almost identical chilled 

rocks associated with the Miocene Cloudy Pass batholith 

(Cater, 1960), but a radiometric potassium/argon age by 

Joan Engels in 1967 indicates these rocks are 44 million 

years old and, hence, temporal equivalents of the other 

upper Eocene rocks of the area. The Old Gib rocks crop 

out in the southeastern part of the Holden quadrangle 

and are confined to the Chiwaukum graben, which 

downdropped prior to emplacement of the Cloudy Pass 

batholith but after or during emplacement of Old Gib

rocks which is probably why erosion did not completely 

remove them long ago. The amount the graben has been 

downdropped, relative to rocks outside the graben, cannot be measured, but unquestionably it must have been 

thousands of feet. Presumably the present exposed part 

of the Old Gib volcanic neck was fairly close to the surface at the time the neck formed because the rocks are of 

typical volcanic aspect and show columnar jointing. On 

the other hand, rocks of nearly if not exactly the same 

age, less than 2.8 km away but east of the graben the 

Larch Lakes and Rampart Mountain plutons have 

typical plutonic affinities rather characteristic of rocks 

emplaced at depths at least approaching the mesozone, 

that is, lack of chilled borders, miarolytic cavities, 

granophyric textures, or finer grained or porphyritic 

satellitic dikes.

The partly eroded volcanic neck on Old Gib Mountain 

is about 2.5 km long and about 1 km wide. It is elongated 

in a north-northwesterly direction parallel to the Entiat 

fault and the foliation of the enclosing rocks. Identical 

rocks also crop out near the floor of the Chiwawa River 

valley, west of Old Gib Mountain, but neither the shape 

of these masses nor their true size are known because 

they are largely concealed by glacial deposits. On Old 

Gib Mountain, cliffs of dacite porphyry in which vertical 

to steeply outward plunging, generally poorly defined 

columns a few meters across are visible locally, rise 

abruptly 300 to 450 m above the lower slopes underlain 

by metamorphic rocks (fig. 83). From some vantage 

points, the neck has a typical pillar-like form. The neck 

is devoid of fragmental or vesicular material, except for 

the remnants of a beveled Pelean spine exposed on the 

summit of the mountain. The lack of layered or bedded 

pyroclastic material, the nearly vertical contacts 

between volcanic and metamorphic rocks, and the 

generally poorly defined columnar joints suggest that 

none of the presently remaining neck was actually above 

ground level when the volcano was active. The dacite on 

Basalt Peak about 3.2 km south of the mapped area is 

identical to the dacite of the Old Gib neck and crops out 

at about the same elevation. The fact that Willis (1953,

TABLE 26. Modal analyses of samples of quartz monzonite from the Rampart Mountain pluton, central Washington

[Leaders (- - -), unable to determine]

Sample

No.

48

49

50

51

52

Plagioclase

29.4

30.6

32.8

43.6

37.8

Potassium

feldspar

26.9

28.0

23.5

12.0

11.1

Quartz

34.8

27.4

33.8

24.8

30.5

Biotite

4.9

6.3

9.0

10.2

10.5

Accessory

and secondary minerals

4.0

7.7

.9

9.4

10.1

Total

mafic

minerals

8.9

14.0

9.9

19.6

20.6

Anorthite in

plagioclase crystals (percent)

Average

25

25

26

26

26

Core

27

27

...

32

Rim

20

20

15

Remarks

Orthoclase and microcline; protoclastic.

Some tourmaline; protoclastic.

Hypidiomorphic.

Hypidiomorphic; coarse-grained,

euhedral epidote.

Hypidiomorphic; coarse-grained,

euhedral epidote.
TERTIARY INTRUSIVE ROCKS 73

TABLE 27. Chemical and spectrographic analyses and norms of a 

composite sample of biotite-quartz monzonite from the Rampart 

Mountain pluton, central Washington

[SiO2 and Al2O.i determined colorimetrically; Fe2C>3, MgO, CaO, and MnO determined by 

atomic absorption; FeO determined volumetrically; NazO and K2O determined by flame 

photometer. Analysts: Wayne Mountjoy, J. D. Mensik, Claude Huffman Jr., G. T. Burrow, 

and H. H. Lipp. Spectrographic analysis by Barbara Tobin]

Chemical analysis 

(percent)

GiO r?Q o

A12O3 ----------15.4

T7_ /~\ r?£?

FeO----------- 1.57

MgO ---------- .53

PaO 9 °,

Na2O---------- 3.81

K o Q r\i

MnO ---------- .06

Total------- 101

Se miquantitative 

spectrographic 

analysis (parts per million)

Ba -----------1,000

Cr ----------- 10

Cu----------- 10

Ga----------- 20

Cf> 7

Sr ----------- 500

V ------------ 70

Y ------------ 10

Yb----------- 1

Zr ----------- 70

Norms

q .... .-..

ah --

hy - -

Total------

- - 35.54

n

en

qo ni

U QQ

Q CC

-- 1 fiQ

-- 1.10

inn nn

Plagioclase composition

OC 1

FIGURE 83. Columnar joints in Old Gib volcanic neck and 

crosscutting basaltic dike, Holden quadrangle. Thickness of dikes 

about 4 m. Trees are less than 3 m high.

p. 793) believed these rocks formed a laccolith rather 

than a flow lends support to the supposition that the 

remaining rocks were below ground level when 

emplaced.

The contact of the neck and the enclosing gneiss is 

visible in only a few places, but in these it is sharp and is 

either vertical or dips steeply inward. The porphyry adjacent to the contact is chilled and contains scattered 

small inclusions of gneiss. Both gneiss and pr rphyry are 

slightly sheared and altered along the contacts and the 

porphyry has a vertical streakiness. Locally, the contact 

is slickensided as though the neck had moved upward as 

a solid pillar. No dikes were observed to radiate from the

neck, although dikes believed to be related are common 

in nearby faults and shear zones. The northeast edge of 

the neck is faulted against gneiss and quartz diorite; the 

fault has been active both before and after the neck was 

intruded, for numerous small, unmapped dacite 

porphyry dikes have been intruded along the fault zone, 

and some of these have been sheared by post-intrusion 

movements along the fault.

The root of the Pelean spine near the center of the 

neck has an outcrop area about 200 m by 150 m but it is 

no longer preserved as a distinct topographic feature. 

The contact between the spine and the surrounding 

porphyry is a vertically fluted, slickensided surface that, 

in many places, dips steeply inward. Caught in the spine 

along the contact are scattered fragments of metamorphic and granitoid rocks that have been faceted and 

striated by dragging along the walls so that they look like 

glaciated pebbles. Some of the rocks in the spine possess 

a strong vertical sheeting that probably resulted from 

shear stresses that developed as the highly viscous lava 

moved upward (fig. 84). Parts of the spine have been 

shattered by explosions so that rocks range from fairly 

large masses of unbrecciated massive porphyry to 

thoroughly brecciated material containing scattered 

fragments of gneiss and granitoid rocks ripped from the 

walls of the conduit at depth. Solfataric emanations 

have altered some of the breccia to limonite-stained 

clay. Surrounding the spine are a few concentric, steeply 

dipping dikes that differ little from the rest of the 

porphyry. Gently dipping dikes of amygadaloidal basalt 

also cut the volcanic neck, but these are probably unrelated to the porphyries.

The Old Gib volcanic rocks, including the mass near 

the river west of Old Gib Mountain, Basalt Peak just 

south of the Holden quadrangle, and related nearby 

dikes, are medium-dark-greenish-gray, conspicuously 

porphyritic dacites and labradorite andesites. Most of

FIGURE 84. Vertical sheeting in Pelean spine in Old Gib volcanic 

neck, Holden quadrangle.
74 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

the rock, particularly in masses west of Old Gib Mountain, is dacite and contains phenocrysts of sodic 

labradorite or calcic andesine, quartz, hornblende, 

biotite, and pseudomorphic nontronitic material; these 

are embedded in a greenish, fine-grained but 

holocrystalline groundmass. The labradorite andesite 

differs from dacite only in the lack of quartz phenocrysts. 

The phenocrysts of sodic labradorite, or calcic andesine, 

are euhedral and oscillatory zoned; zones within a single 

crystal may range from An??, to An.ss. Many of these 

crystals are veined by albite. Most of the quartz crystals 

are rounded and resorbed, but a few are doubly terminated unresorbed pyramids. Fresh hornblende is rare 

as most of it has altered to fine-grained aggregates of 

chlorite, green nontronitic material, and lesser quantities of titanite and magnetite. Some of the hornblende 

and its alteration products preserve the outline of pyroxene crystals, but no unaltered pyroxene was seen. Biotite 

as brown euhedral crystals is fairly common in some 

localities but absent in others. Stilbite is common, some 

of it occurring along and wedging apart cleavage plates 

of biotite as does rare prehnite. The groundmass is a very 

fine grained aggregate of andesine, quartz, nontronite, 

and magnetite. Most plagioclase grains in the groundmass are equidimensional, have irregular indistinct 

borders, and contain numerous mafic inclusions, but 

some are lathlike and arranged in flow lines. In addition 

to andesine is considerable clear, fine-grained albite that 

replaces earlier formed minerals. The greenish color of 

the groundmass is due to chlorite and nontronite.

Chemical and spectrographic analyses and norms of 

dacite from Old Gib Mountain are given in table 28. The 

major oxides are plotted on a variation diagram (fig. 70) 

and the norms are plotted on figure 71.

JOINTING IN VOLCANIC NECK

Well-defined curved columns, not to be confused with 

the columns previously mentioned, several centimeters 

to 1.5 m across but mostly less than 1 m, are common in 

the marginal porphyry. At the contact, these are 

horizontal and, hence, nearly normal to it, but within 3 

to 5 m they bend upward to steep or nearly vertical attitudes. Farther inward these columnar joints die out, 

and the rock is irregularly jointed.

The growth of these curved columns poses a problem, 

for, as a rule, columns in volcanic rocks grow normal to 

isothermal surfaces (Waters, 1960; James, 1920). They 

grow in this direction because a mass of cooling magma 

is free to move or shrink normal to a cooling or isothermal surface (a contact, for example), whereas there is no 

freedom of movement parallel to this surface unless fracturing occurs. However, it is difficult to visualize how 

isothermal surfaces could curve sharply enough at the

Chemical anal 

(percent)

SiO2 ---------

Fe2O3 --------

FeO----------

MgO ---------

CaO ---------

K n

H f^-i.

H

r\

T1:*"*

P

r\

MnO---------

Total-------

ysis

-64 46

1 f~* 1C

- 2.10 

- 2.08 

- 1.75 

- 3.93 

- 3.82 

- 1.52 

- 1.68 

- 1.08 

- .38 

- .13 

.10 

.59

99.77

Semiquantitative 

spectrographic 

analyses (parts per million)

Ba 

Co 

Cr 

Cu 

Ga 

Ni 

Sc 

Sr 

V -

Y -

Yb 

Zr

1 C

7OO

........... 7

q

1C

........... 7

q

1 *>

7flf>

........... 70

1C

1 C

........... 70

Norms

q ...........

ah

hy --------

il ...........

ctp

Tntfll

q 9C

qq qq

 t c 07

fi 1Q

O CO

q 14

qo

-- 1.17

1 nn nn

Plagioclase composition

--32.4

TABLE 28. Chemical and spectrographic analyses and norms of a 

composite sample of dacite from the Old Gib volcanic neck, Holden 

quadrangle

[Standard analysis by D. F. Powers. Spectrographic analysis by Harry Bastron and P. R.

Barnett]

depths at which the columns probably formed around 

the base of Old Gib volcanic neck to account for the 

bending of the columns. Hunt (1938) offered an explanation for curved columns in volcanic necks that seems 

adequate to explain the phenomena he described when 

he pointed out that "At any given point, fracturing may 

be along either of two sets of planes, one dipping outward 

toward the sides of a pipe, the other dipping inward. The 

set dipping outward is favored by cracks extending 

downward from the surface because contraction is 

greater toward the sides than toward the center of the 

pipe." This mechanism, however, seems inadequate to 

explain the curved columns in the Old Gib volcanic neck 

because these formed at considerable depth, remote 

from the upper cooling surface, and the joints die out not 

many meters from the contact into irregular fractures. 

Obviously, columnar joints will grow normal to the surface of greatest tensile stress, a surface which normally is 

parallel to isothermal surfaces. But a column of magma, 

the molten core of which is moving as the marginal parts 

are solidifying and freezing to the walls of the conduit, 

develops dynamic stresses in these marginal parts, 

which are at angles to the thermal stresses resulting from 

cooling. Under these circumstances, columnar joints will 

not form normal to isothermal surfaces but to a surface 

of maximum tensional stress that will be some resultant 

plane; such joints would curve down if, at the time of 

their formation, the magma is moving up. It seems 

likely, however, that the magma was moving up at the 

time the marginal columns in the Old Gib volcanic neck 

formed, and if this is true, then the columns are curved 

in a direction opposite to what they should be if they are
TERTIARY INTRUSIVE ROCKS 75

strictly tensional features. What seems to be a 

reasonable and possible explanation is that these 

columns started in the normal manner because of tension resulting from cooling, but that they were then extended partly because of continued tensional stresses 

resulting from continued cooling and partly because of 

shear stresses resulting from movement of the magma. 

Furthermore, they would curve to conform to direction of 

maximum shear and would therefore bend upward. 

Those joints more or less radial to the neck would continue as tensional fractures, whereas those more or less 

concentric to the walls of the neck would become shear 

fractures.

INTRUSIVE BRECCIA

On the east side of the valley at the head of Klone 

Creek are outcroppings of an intrusive breccia. Along the 

southwest side of the largest outcrop of breccia, 

hornblende-biotite diorite is exposed, but contacts with 

the breccia were not seen, and the relation of the breccia 

to other rocks is not known. Possibly the intrusive breccia may be related to the Cardinal Peak pluton, but the 

nature of the hornblende-biotite granodiorite forming 

much of the matrix of the breccia strongly suggests a 

kinship with the late Eocene intrusions. Some of the 

granodiorite closely resembles biotite-quartz monzonite 

and granodiorite, and some resembles the hornblendebiotite-quartz diorite. The intrusive breccia consists of 

blocks and lenses of various types of gneiss engulfed in 

granodiorite, and the whole is cut by much leucocratic 

granodiorite. The blocks and lenses of gneiss have a rude 

parallelism and trend N. 30°-70° E. and dip east at 

moderate angles. Much of the breccia and some of the 

porphyry dikes that cut it are badly shattered.

HORNBLENDE-BIOTITE-QUARTZ DIORITE

Hornblende-biotite-quartz diorite crops out extensively in the northwest quarter of the Lucerne 

quadrangle and the adjacent parts of the Holden 

quadrangle. Most of the bodies are dikes a few meters to 

a few tens of meters thick, but two masses, one on 

Ninemile Creek and the other south of Entiat Meadows, 

are 1.5 km or more across, and a third at the mouth of 

Tenmile Creek is nearly 1 km wide. Numerous dikes 

branch from these larger intrusions, and many of 

these especially where they intrude the Cardinal Peak 

pluton are rather low dipping. In many places, the 

hornblende-biotite-quartz diorite is closely associated 

with biotite-quartz monzonite and granodiorite, which it 

resembles in outcrop appearance, but wherever crosscutting relations could be determined, the quartz diorite is 

generally older and commonly occurs as inclusions in 

quartz monzonite and granodiorite. In the vicinity of the

lower part of Ninemile Creek where biotite-quartz monzonite intricately intrudes the quartz diorite, however, 

the quartz diorite appears to have been at least still 

partly molten when the quartz monzonite was intruded. 

In the Holden mine, dikes and irregular masses consisting of intricate intermixtures of the hornblendebiotite-quartz diorite unit and the biotite-quartz monzonite and granodiorite unit containing abundant inclusions of gneiss, schist and ore are of common occurrence 

in Duncan Hill rocks (fig. 85).

Hornblende-biotite-quartz diorite is a gray, commonly 

foliated rock ranging from very fine grained (grains 

mostly 0.1 mm across or less) to fine medium grained 

(grains as much as 1.5 mm across) (fig. 86); some is distinctly porphyritic, containing phenocrysts of andesine 

and biotite about 5 mm across. Grain size seems to bear 

little relation to the size of intrusion; the larger masses 

are rather fine grained throughout but vary somewhat 

from place to place; dikes are more variable and include 

both the finest and coarsest grained rocks. Probably the 

most characteristic feature is a pervasive foliation 

resulting from the parallelism of biotite flakes. This 

foliation, which ranges from nearly imperceptible to 

strong, is a flowage feature and usually parallels the 

nearest contacts, but in some places it is swirled.

Contacts with older rocks are sharp in most places or 

gradational through only a centimeter or two, but where 

the hornblende-biotite-quartz diorite invades hornblende gabbro of Riddle Peaks the contact is highly irregular, although sharp. Near the contact with 

hornblende gabbro, the quartz diorite contains abundant inclusions of gabbro, but inclusions of other rocks, 

such as quartz diorite and granodiorite of Cardinal Peak,

FIGURE 85. Intermixed hornblende-biotite-quartz diorite (qd), 

biotite-quartz monzonite (qm), and inclusions of biotite schist(s), 

showing various stages of alteration, at the Holden mine, Holden 

quadrangle. Width of photographed area about 1 m.
76 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Fioi'RE 86. Hornblende-biotite-quartz diorite in the Holden mine, 

Holden quadrangle.

or of metamorphic rocks, are rare. Where the 

hornblende-biotite-quartz diorite has been intruded by 

later rocks, particularly the biotite-quartz monzonite 

and granodiorite, the contacts are complex and irregular. 

East of Ninemile Creek is an intrusive contact between 

the Railroad Creek pluton and the hornblende-biotitequartz diorite. Here the Railroad Creek pluton has 

numerous irregular dikes in the quartz diorite, and the 

Railroad Creek rocks have a streaky appearance owing to 

protoclasis that parallels the contact.

Thin sections of hornblende-biotite-quartz diorite 

show the rock to consist of 50 to 60 percent plagioclase, 

20 to 30 percent quartz, 7 to 15 percent biotite, 0 to 8 percent hornblende, and generally less than 1 percent potassium feldspar. Titanite, allanite, and apatite are accessory. Andesine, having an average composition of about 

An4o, is the predominant plagioclase, but in some rocks,

otherwise indistinguishable, the plagioclase may have an 

average composition as sodic as An:i2 , and in the mass 

centering around Ninemile Creek, much of the 

plagioclase is sodic labradorite and the rock is a quartz 

gabbro. Plagioclase is strongly zoned; some crystals 

range from cores of Anfio to rims of An-2o. Scattered 

crystals occurring as phenocrysts in the slightly 

porphyritic varieties have patchy zoning and numerous 

oscillatory zones, whereas the crystals in the groundmass 

show fewer oscillatory zones but very strong progressive 

zoning. Quartz is either interstitial or occurs as an aggregate of interlocking, sutured grains. Orthoclase is rare 

and interstitial. A little myrmekite borders some of the 

orthoclase grains where they are in contact with 

plagioclase. Biotite occurs as highly pleochroic shreds 

ranging from light straw yellow to dark, almost opaque 

muddy brown. Hornblende is either anhedral or subhedral; most of it is pleochroic in shades of green, but 

some, especially that in some of the gabbroic facies, is 

nearly colorless and only slightly pleochroic. Alteration 

products are rare in most rocks, but some of the mafic 

minerals are chloritized, and most sections contain a little epidote.

Textures are typically hypidiomorphic and commonly 

have a fairly strong alinement of plagioclase laths, 

biotite flakes, and hornblende needles, suggestive of 

flowage. Much of the rock is slightly porphyritic and is 

characterized by a few scattered phenocrysts of euhedral 

plagioclase.

Modal analyses (table 29; fig. 87) show that these 

rocks vary in composition more than most of the late 

Eocene intrusive rocks. Chemical analyses are shown in 

table 30, and the norms are plotted in figure 71. Locations of modally analyzed specimens are shown in figure

TABLE 29. Modal analyses of samples of late Eocene hornblende-biotite-quartz diorite, central Washington

Sample 

No.

9

11

12

21

22

23

42 

43

44

45

46

Plagioclase

52.2

56.4

56.2

50.5

54.0

54.7

52.2 

61.8

61.2

57.6

53.8

Potassium 

feldspar

0.3

.4

.7

1.4

.3

1.6

.3 

.1

1.6

0

2.5

Quartz

32.2

29.5

33.1

29.4

25.7

27.3

32.2 

18.8

19.1

22.9

26.4

Biotite

14.7

10.8

2.6

13.5

13.0

11.3

14.7 

12.9

15.4

16.1

13.4

Hornblende

0.3

2.7

1.1

5.0

5.9

3.6

.3 

6.0

1.1

2.8

2.7

Accessory 

and secondary minerals

0.3

.2

6.3

.2

1.1

1.5

.3 

.4

1.6

.6

1.2

Total 

mafic 

minerals

15.3

13.7

10.0

18.7

20.0

16.4

15.3 

19.3

18.1

19.5

17.3

Anorthite in 

plagioclase crystals (percent)

Average

43

41

37

40

40

37

38 

38

37

40

37

Core

60

60

55

56

52

43

51

42

47

54

43

Rim

20

22

22

23

21

23

21 

29

20

30

23

Remarks

Hypidiomorphic.

Do.

Subparalled mineral

alinement; hypidiomorphic.

Slightly porphyritic.

Subparallel mineral

alinement; hypidiomorphic.

Hypidiomorphicprotoclastic.

Hypidiomorphic. 

Subparallel mineral

alinement; hypidiomorphic.

Subparallel andesine

laths; hypidiomorphic.

Subparallel mineral

alinement; hypidiomorphic.

Subparallel mineral

alinement; xenomorphic.
TERTIARY INTRUSIVE ROCKS 77

TABLE 30. Chemical and spectrographic analyses and norms of a 

composite sample of late Eocene hornblende-biotite-quartz diorite, 

central Washington

[SiC>2 and Al2Os determined colormetrically; Fe2O.i, MgO, CaO, and Mn determined by 

atomic absorption; Na2O and K2O determined by flame photometer; FeO determined 

volumetrically. Analysts: Violet Merritt, H. H. Lipp, G. D. Shipley, and G. T. Burrow. 

Spectrographic analysis by Harriet Neiman]

Chemical analysis 

(percent)

SiO2 --

A12O3 --

Fe2O3 -

FeO---

MgO--

PaO

Na2O--

K c\

MnO--

Total

...---.-14.4

........ 4.45

Q C

2

1 £

Q QO

3 QQ

-------- 1.41

-------- 08

inn nn

am

Ba 

Co 

Cr

Cu 

Ga

Ni 

Pb 

Sc 

Sr 

V -

Y -

Yb 

Zr

Semiquantitative 

spectrographic 

lysis (parts per million)

cno

1 C

Qf)

1 C

. --.-......-20

............. 10

............. 10

............. 20

.............700

............-150

------------- 20

------------ 2

.....---.....100

Norms

q ...........

ah

hy ..........

Total------

OQ CO

OQ no

-- 19 48

- 8 9Q

1 C

-- 6.46

100 00

Plagioclase composition

--40.4

RAILROAD CREEK PLUTON AND ASSOCIATED ROCKS

The Railroad Creek pluton occupies the northwest 

part of the Lucerne quadrangle, adjacent parts of the 

Holden quadrangle, and extends an undetermined but 

probably short distance farther north. It has a maximum 

width of about 6.5 km. Identical rocks believed to connect with the pluton under Bearcat Ridge crop out 

between Bear Creek and Lake Chelan; smaller masses 

crop out west of Mirror Lake and on the ridge north of 

the head of Little Creek. Satellitic dikes and small irregular masses are widely scattered over much of the 

northern part of the Lucerne quadrangle.

The Railroad Creek pluton, consisting largely of 

granodiorite, is elongate roughly parallel to the strike of 

the foliation of the host rocks, and locally the contact is 

concordant, but in most places the contact cuts across 

the foliation or layering at various angles. In general, 

contacts are sharp, but the characteristics of the contact 

and the border rocks near the contact vary from place to 

place. East of Domke Lake, the contact is sharp, the 

granodiorite is massive, and the enclosing gneiss appears 

to be unaffected. In most places, however, the 

granodiorite becomes increasingly foliated as the contact 

is approached, and a few meters of the adjacent host 

rocks are somewhat granitized. In many places, the host 

rocks near the contact are interlayered with and cut by 

numerous dikes of granodiorite. Particularly complex is 

the contact between the Railroad Creek pluton and the 

hornblende gabbro north of Riddle Peaks. Here a septum 

of hornblende gneiss separating the hornblende gabbro 

from the pluton is intricately riddled with dikes of

Quartz

Piagiociase 35

Potassium 

feldspar

FlGURF, 87. Plot of modes of hornblende-biotite-quartz diorite 

samples from Holden and Lucerne quadrangles on a quartzpotassium feldspar-plagioclase diagram. Sample analyses are given 

in table 29.

granodiorite, some of which extend into the hornblende 

gabbro. Abundant inclusions of both gneiss and 

hornblende gabbro occur in the granodiorite near the 

contact. Inclusions are also numerous in many other 

places near the contact, but are generally rare nearer the 

center of the pluton. At no place were seen contact complexes characterized by coarse hornblendite similar to 

those bordering some of the older hornblende-quartz 

diorite plutons. The pluton widens at depth; the 

southwest contacts dip outward, whereas the northeast 

contact is nearly vertical and dips steeper than the 

enclosing gneisses.

Contacts of dikes and small masses related to the 

Railroad Creek pluton are sharp, and margins of some of 

the smaller dikes are chilled. The contact of the large 

dike on Ninemile Creek locally forms lit-par-lit zones.

There has been some tendency for the pluton to force 

or shoulder aside the host rocks; gneisses adjacent to the 

contact are crumpled, but for the most part the pluton 

seems to have made room for itself by some other means 

as is evident near Lucerne Mountain and near Bear 

Creek, where enclosing rocks were removed or destroyed. 

Undoubtedly, stoping was one means by which the 

pluton made room for itself, but the scarcity of inclusions of country rocks, except locally near contacts, suggests the process was not a major factor. Replacement 

and granitization fusion seem to have played even a 

smaller role in solving the pluton's room problem at 

least to the depth presently exposed.
78

48° 

15'

INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

120° 45'

EXPLANATION

Hornblende-quartz gabbro. Copper 

Peak and Holden Lake plutons

Granodiorite and quartz monzonite 

Railroad Creek pluton

Biotite-quartz monzonite and 

granodiorite

Hornblende-biotite-quartz diorite

 Contact

 16 Sample locality

 //_=

FIGURE 88. Map showing location of modally analyzed samples from late Eocene plutons, central Washington.

The rocks of the pluton vary both in composition and 

in texture. Most of the rock is granodiorite but also included are quartz diorite and quartz monzonite. Quartz 

monzonite, in particular, is conspicuous because it forms 

lighter colored, irregular masses that in some places cut 

the somewhat older granodiorite; elsewhere quartz monzonite grades into granodiorite as does quartz diorite. 

The typical granodiorite and quartz diorite are indistinguishable in outcrop and are light gray and 

medium grained (fig. 89). Most of the rock is massive 

and structureless, but near contacts, some is foliated and 

commonly contains more hornblende than elsewhere. 

The quartz monzonite is texturally similar but is light 

gray to white, and some is stained because of oxidized 

pyrite, a rather common constituent mineral in much of 

the quartz monzonite. No attempt was made to separate 

the different kinds of rock on the map because of their 

generally gradational nature, the mapping time limitations, and dense brush, but the impression was that distribution of rock types was erratic.

The rocks of the Railroad Creek pluton contain 

variable amounts of plagioclase, quartz, potassium feldspar, biotite, and hornblende; titanite, apatite, and 

zircon are accessory. Chlorite, sericite, epidoteclinozoisite, and opaque minerals are alteration 

products. Other minerals found in some specimens are

FIGURE 89. Biotite granodiorite from the Railroad Creek pluton, 

Lucerne quadrangle.
TERTIARY INTRUSIVE ROCKS 79

muscovite, allanite, and pyrite. Most of the rocks are 

hypidiomorphic granular, but near the contacts some of 

the rocks are protoclastic. Plagioclase occurs as irregular 

to euhedral grains from a fraction of a millimeter to as 

much as 3 mm across. Most of the larger grains are oscillatorily zoned, and many show patchy zoning; the extreme observed range of composition was from Anifi on 

the rims of crystals to An in the core, but the usual 

range was about An2 o to An4 o. Average composition of 

plagioclase in most of the quartz diorite and granodiorite 

was about An:{ 7, but in some of the leucocratic quartz 

monzonite, the average composition was An2 r>. Calcic 

cores of crystals in some sections are clouded with 

sericite. Nearly all grains show albite twinning, and 

combined Carlsbad-albite twinning is common; twinning according to other laws, particularly pericline, occurs but is less common. Grains of plagioclase that are in 

contact with orthoclase are mostly rimmed by 

myrmekite.

Most of the potassium feldspar is orthoclase, but some 

microcline occurs in a few sections. Most of the 

orthoclase is microperthitic. All the potassium feldspar 

is anhedral and is either interstitial or replaces earlier 

formed minerals.

Quartz is also late and either replaces other minerals 

or is interstitial. Much of it occurs as irregular mosaics of 

grains having interlocking, sutured borders; but single 

interstitial grains and myrmekitic intergrowths are 

numerous. Nearly all the quartz, except for that in myrmekite, is strained and shows flamboyant extinction.

Biotite is the most abundant of the mafic minerals and 

in some thin sections, the only primary mineral. Much of 

it occurs as irregular anhedral shreds, but faces of many 

crystals parallel to cleavage are well defined. Locally, 

particularly near the contacts, the biotite flakes are subparallel and impart a foliation to the rock. The 

pleochroic formula is generally X, light ye1 low; Y = Z, 

reddish-brown. Some of the biotite has partly altered to 

chlorite. Small amounts of hornblende are present in 

most sections, but generally only rocks near the contacts 

contain more than 1 or 2 percent. Crystals form elongate 

anhedra that have been partly resorbed, or they may be 

euhedral and show well-formed six-sided sections. Some 

show replacement by biotite. Most hornblende is 

pleochroic in various shades of green. In the pass at the 

head of Riddle Creek, hornblende in rocks near the contact are pleochroic from yellowish brown to bluish green. 

This hornblende may be relict from the invaded gabbro; 

in fact, much of the hornblende commonly present near 

contacts may be the result of contamination.

Titanite is the most conspicuous of the accessory 

minerals but is less common than in many other plutons 

of the area. Most of it occurs as typical diamond-shape

grains as much as 2 mm long, but some is anhedral. A 

grain or two of allanite was seen in a few sections, but it 

is far less common than in the Duncan Hill pluton. Tiny 

scattered needles of apatite are ubiquitous. Grains of 

zircon much less than 1 mm across are common in 

biotite flakes where they are bordered by pleochroic 

halos.

Most of the Railroad Creek rocks are fairly fresh, and 

none are badly altered. In most thin sections, however, a 

little of the biotite has altered to chlorite, and less commonly, calcic cores of plagioclase show some dusting 

with sericite. Occasional granular aggregates of 

clinozoisite replace plagioclase, and epidote replaces 

mafic minerals. Pyrite replaces biotite in some of the 

light-colored quartz monzonite.

Larger dikes and irregular intrusive masses related to 

the Railroad Creek pluton closely resemble rocks in the 

pluton, but smaller dikes and masses are eenerallv finer 

grained or slightly porphyritic (fig. 90). Some have 

chilled, fine-grained margins. A greater range of compositions occurs in the dikes than in the main pluton. Some 

of the dikes in the Riddle Peaks area are rather fine 

grained, nearly white, and contain only 5 to 7 percent 

dark minerals and yet have no potassium feldspar and 

hence are quartz diorites. These have hypidiomorphic, 

seriate textures. Other dikes of similar appearance in the 

same area have almost xenomorphic textures and contain nearly equal amounts of plagioclase and potassium 

feldspar. Most of these are foliated because of alined 

biotite flakes.

Modal analyses (table 31; fig. 91) indicate a considerable spread in composition. Location of modally 

analyzed specimens are shown in figure 88. Chemical 

and spectrographic analyses and norms are given in 

table 32, and a plot of the norms in figure 71.

1

FIGURE 90. Porphyritic biotite-quartz diorite dike rock from the 

Railroad Creek pluton, Lucerne quadrangle.
80 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 31. Modal analyses of samples of granodiorite and quartz monzonite from the Railroad Creek pluton,

Lucerne quadrangle

[Leaders (- - -), unable to determine]

Sample

No.

13

14

15

16

17

18

19

20

24

28

29

30

31

32

33

38

39

40

41

47

48

49

Plagioclase

52.7

43.7

65.7

35.4

59.4

31.3

39.2

38.6

45.9

44.0

36.4

55.6

52.0

46.0

48.0

54.3

54.1

40.9

51.2

31.6

37.5

59.3

Potassium 

feldspar

7.3

1.5

0

26.0

3.2

32.1

4.7

18.0

15.0

8.8

12.0

4.4

11.2

6.4

9.3

13.1

12.9

20.4

17.3

26.1

20.6

4.3

Quartz

23.3

36.4

25.9

27.7

20.6

32.7

40.9

32.3

27.1

27.2

26.3

27.0

30.8

38.1

28.7

21.1

23.4

32.3

26.4

39.8

32.2

28.6

Biotite

0.3

7.5

6.7

3.6

13.9

3.3

14.2

10.7

11.2

16.9

23.3

10.0

5.3

9.0

8.2

17.3

8.4

5.7

4.8

1.8

9.2

7.6

Hornblende

1.9

10.5

.6

6.4

2.5

0

.8

0

0

2.1

1.0

1.8

.4

.3

3.9

3.7

.6

0

0

0

0

0

Accessory 

and secondary minerals

14.5

.4

1.1

.9

.4

.6

.2

.4

.8

1.0

1.0

1.2

.3

.2

1.9

.5

.6

.7

.3

.7

.5

.2

Total 

mafic 

minerals

16.7

18.4

8.4

10.9

16.8

3.9

15.2

11.1

12.0

20.0

25.3

13.0

6.0

9.5

14.0

21.5

9.6

6.4

5.1

2.5

9.7

9.8

Anorthite in 

plagioclase crystals (percent)

Average

35

38

38

36

32

_

37

38

28

_

40

Core

38

40

48

40

...

58

40

41

...

 .

48

Rim

25

23

33

18

.-.

17

20

18

16

TABLE 32. Chemical and spectrographic analyses and norms of a 

composite sample of biotite granodiorite from the Railroad Creek 

pluton, Lucerne quadrangle

[SiC>2 and AbOs determined colorimetrically; Fe2C>3, MgO, CaO, and MnO determined by 

atomic absorption; FeO determined volumetrically; NasO and K2O determined by flame 

photometer. Analysts: Wayne Mountjoy, J. D. Mensik, Claude Huffman Jr., G. T. Burrow, 

and H. H. Lipp. Spectrographic analyses by Barbara Tobin]

Chemical analysis 

(percent)

SiO2 ----------70.1

A12O3 ----------15.6

Fe2O3 --------- .34

FpO - - - . 91^

MgO ---------- .66

Cat) "3 1

Na2O---------- 3.91

K2O----------- 2.50

MnO ---------- .05

TVrfnl Q8

Semiquantitative 

spectrographic 

analysis (parts per million)

Ba --------- 1,000

Co--------- 10

Cr --------- 20

Pn C

Ga --------- 30

Ni --------- 10

Sc --------- 10

Sr --------- 500

V---------- 100

V Ifi

Yb--------- 1.5

Zr ----------- 150

Norms

q .............28.95 

or---------.---15.01

V f\n £*(\

an ------------15.63

hy ------------ 5.47

mt ------------ .50

Total ------- 100.00

an ------------31.7

COPPER PEAK AND HOLDEN LAKE PLUTONS

The Copper Peak and Holden Lake plutons are shown 

on the geologic map of the Holden quadrangle (Cater 

and Crowder, 1967) as of questionable Miocene age. 

They were so considered because of their general lack of

Quartz

Plagiociase

Potassium 

feldspar

FIGURE 91. Plot of modes of granodiorite and quartz diorite samples 

from the Railroad Creek pluton, Lucerne quadrangle, on a quartzpotassium feldspar-plagioclase diagram. Sample analyses are given 

in table 31.

similarity to other late Eocene rocks, their rather close 

resemblance to the labradorite quartz diorites of the 

Miocene Cloudy Pass batholith, and the fact that dikes
TERTIARY INTRUSIVE ROCKS 81

satellitic to the Copper Peak pluton in the Holden mine 

are postore, whereas the ore is genetically related to the 

Duncan Hill pluton. Later investigation, however, indicated that in places these plutons are cut by the late 

Eocene biotite-quartz monzonite and granodiorite and, 

hence, are older, but because the quartz gabbro of the 

plutons cuts ore, the plutons are also late Eocene.

The Copper Peak and Holden Lake plutons consist of 

hornblende-quartz gabbro, a rock that also forms 

numerous dikes and an elongate mass about 2.5 km east 

of Holden Lake. Largest of the intrusions is the Holden 

Lake pluton north of Holden Lake, which has a width of 

about 1.5 km and extends from an unknown distance 

north of the quadrangle more than 2 km into it. The Copper Peak pluton crops out on the north side of Copper 

Peak and is a little more than 1.5 km long and about 0.5 

km wide, although dikes of the rock are widespread as 

much as 1.5 km farther west.

Contacts of all masses, except in the two larger 

plutons, are sharp, but in these two, contacts are either 

sharp or consist of spectacular contact complexes. 

Complexes associated with the Copper Peak pluton are 

particularly spectacular because much of the pluton intrudes the intricate melange of rocks constituting the 

contact complex surrounding the northwest end of the 

Duncan Hill pluton. Here, unfortunately, exposures are 

rather poor, the brush dense, and it was impractical to 

attempt to unravel the incredibly complicated mixture 

of rock types. Hornblendite, gabbro, diorite, quartzbearing rocks, partly assimilated gneisses, and all possible gradations between rock types are stirred together in 

chaotic jumbles. The contact complex bordering the 

southwest side of the Holden Lake pluton is well exposed, however, and here the hornblende-quartz gabbro 

intrudes its own contact complex, and the contact 

between the two is sharp. Where visible elsewhere, the 

hornblende-quartz gabbro grades into its bordering complex. At contacts of gabbro and hornblende-quartz 

diorite gneiss, the host gneiss loses its foliation, the grain 

size coarsens, and the rock becomes compositionally 

heterogeneous. Irregular dikes and masses of mostly 

leucocratic gabbro engulf blocks of host rocks or 

penetrate them as lit-par-lit injections. Many of the 

thinner dikelets of leucocratic gabbro contain a central 

layer of coarse hornblende crystals. Examination of thin 

sections shows that minerals of the host rocks in the 

complex have reverted to the same compositions as those 

of the minerals in the injected igneous material, 

although the crystalloblastic texture of the nonigneous 

material is retained.

Hornblende-quartz gabbro is a medium-grained, gray, 

massive rock, in which plagioclase, hornblende, quartz, 

and varying quantities of biotite are visible to the unaided eye (fig. 92). The rather sizeable mass east of 

Holden Lake contains more biotite than hornblende but

FIGURE 92. Hornblende-quartz gabbro (finer grained) cut by biotitequartz monzonite (coarser grained) from the Holden Lake pluton, 

Holden quadrangle.

is otherwise identical to the rest of the quartz gabbro. 

The rock within a given mass or within different masses 

varies little in appearance, except in the contact complexes that border parts of the two larger plutons. In thin 

section, the texture is seen to range from xenomorphic to 

hypidiomorphic. The plagioclase is labradiorite, mostly 

having an average composition of about Aneo, but some 

crystals are as low as An5s, and others as high as An6r,. 

Many of the grains show a few oscillatory zones, but the 

compositional range is rather small, mostly less than 10 

percent variation in anorthite content. Patchy zoning is 

ubiquitous. Sericitic alteration of plagioclase is fairly 

common, particularly in the more calcic cores of grains. 

Hornblende is distinctive; it occurs as mottled lightolive-green and light-brown, irregular, anhedral grains 

and shreds. Much of it has altered to fine-grained mats 

of actinolite or, in places, chlorite. Biotite occurs as 

separate grains and as replacements of amphibole; the 

pleochroism is very strong and ranges from nearly 

colorless light straw yellow to deep, bright red. 

Magnetite, which commonly makes up about 5 percent 

of the rock, is generally closely associated with biotite 

and may have separated as hornblende altered to biotite. 

Quartz is interstitial. Orthoclase is rare and occurs only 

along tiny seams and fractures in the rock. Apatite and 

titanite in varying amounts are accessory.

Modal analyses of hornblende-quartz gabbro are given 

in table 33 and a chemical analysis in table 34. The 

modes are plotted in figure 93 and the norms in figure 71.
82 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 33. Modal analyses of samples of hornblende-quartz gabbro from the Copper Peak and Holden Lake plutons, Holden quadrangle

Sample

No.

1

2

3

4

5

6

7

8

Plagioclase

64.3

62.3

61.4

51.5

58.0

54.7

55.3

37.0

Potassium

feldspar

0

0.3

0

0

.2

.1

0

1.6

Quartz

4.4

5.4

5.6

11.9

18.8

18.9

5.6

5.5

Biotite

3.1

1.2

8.9

11.3

16.3

14.7

1.2

.6

Hornblende

22.1

15.5

20.7

22.2

6.2

6.3

35.5

34.5

Accessory

and secondary minerals

6.1

15.3

3.4

3.1

.5

5.3

2.4

20.8

Total

mafic

minerals

31.3

32.0

33.0

36.6

23.0

26.3

39.1

35.9

Anorthite in

plagioclase crystals (percent)

Average

54

54

58

52

57

56

56

56

Core

70

70

75

58

64

65

77

78

Rim

41

33

42

35

26

9

28

16

Remarks

Hypidiomorphic .

Do.

Hypidiomorphic; subparallel

plagioclase crystals.

Hypidiomorphic .

Hypidiomorphic -cataclastic.

Hypidiomorphic; subparallel

plagioclase crystals.

Hypidiomorphic .

Do.

TABLE 34. Chemical and spectrographic analyses and norms of 

quartz gabbro from the Holden Lake pluton, Holden quadrangle

[Standard rock analysis by E. S. Daniels]

Chemical analysis 

(percent)

o */~\

AlaOs---------

Fe2O3 --------

T?n r\

MgO ---------

r-,,n

Na2O---------

K

r\

H o_i_

H c\

T'JO

P2 05 ---------

MnO ---------

CO2 ----------

F ------------

Subtotal----

Total ------ -

CO Of?

- 18.91

- .72

c 01

- 4.01

Q f\C

_ o qc

cc

- 1.17

09

9 ^1

12

02

- .01

- .06

100.07 

no

100.04

Semiquantitative 

spectrographic 

analysis (parts per million)

Ba

Co 

Cr

Cu 

Ga

Ni 

Sc 

Sr 

V -

Y -

Zr

............ .500

..... 20

en

en

............. 20

1C

on

700

.............200

on

en

Norms

q ----- 

nVi

hy - 

bi-----

tn-----

fr -----

hl-----

Total

Plagiocl

Q 36

OC Q"7

----.---31.84

------.-15.97

-------- 2 11

-------- .77

.------. 4 Q1

........ 27

nc

n°.

.......100.00

ase composition

--------54.2

BIOTITE-QUARTZ MONZONITE AND GRANODIORITE

Biotite-quartz monzonite and granodiorite crop out 

more or less coextensively with hornblende-biotitequartz diorite, but unlike the quartz diorite, occur as far 

south as Fern Lake. The two units seem to be closely 

related, but biotite-quartz monzonite and granodiorite 

are somewhat younger. In many places in the Lucerne 

quadrangle, the two units are so intricately scrambled 

that separate mapping was impractical, and areas of 

such mixed rocks are shown as being underlain by the 

dominant type; thus, masses labeled as biotite-quartz 

monzonite and granodiorite in the Sevenmile Creek 

drainage, in places, are almost half quartz diorite. The 

intrusive relations between the two units are particularly 

well displayed in the roadcut near the east edge of the

Quartz

Plagioclase

Potassium 

feldspar

FIGURE 93. Plot of modes of hornblende-quartz gabbro samples from 

the Copper Peak and Holden Lake plutons, on a quartz-potassium 

feldspar-plagioclase diagram. Sample analyses are given in table 33.

Holden quadrangle east of Holden. In many places, 

however, distinguishing between the two units in 

isolated outcrops is difficult because of their locally very 

similar appearances.

The largest of the intrusions of biotite-quartz monzonite and granodiorite crops out east of Wilson Creek 

and has a spectacular array of dikes of various sizes that 

follow a system of flat joints; these dikes are most 

numerous in the Cardinal Peak pluton. Similar flat dikes 

are also satellitic to the mass between Tenmile and 

Ninemile Creeks but are less common. Where the rock 

intrudes the Duncan Hill pluton, it forms highly irregular small masses that were not separately mapped. 

These are particularly abundant in the contact complex
TERTIARY INTRUSIVE ROCKS 83

at Buckskin Mountain and between Anthem Creek and 

Fern Lake.

The biotite-quartz monzonite and granodiorite are 

mostly fine- to medium-grained, light-gray to nearly 

white rock, the quartz monzonite tending to be lighter 

because of generally less biotite (fig. 94). Most of the 

rock has a pronounced foliation due to alined biotite 

flakes. Some rocks are slightly porphyritic. Foliation is 

mostly parallel to the attitudes of the dikes, but, surprisingly, some dikes have a foliation parallel to that of 

the regional foliation, regardless of the trend of the dikes 

themselves. Pitcher and Berger (1972) described similar 

oblique foliation in dikes cutting the Donegal pluton 

and ascribed the obliquity to movement of the dike walls 

relative to each other. The general aspect conveyed by 

these relations in the quartz monzonite and granodiorite, 

however, is that of rocks that have been regionally 

metamorphosed and recrystallized to the regional alinement. Microscopic study quickly dispels this erroneous 

assumption, however, because the texture of both the 

quartz diorite and the slightly younger dikes that cut it is 

typically protoclastic. Euhedral crystals of plagioclase 

showing numerous oscillatory zones are broken and 

abraded, and late quartz, orthoclase or perthite, and 

biotite have crystallized along shearing planes that 

paralleled the regional metamorphic fabric of the area. 

Some of the biotite has been warped by still later movement. At one locality, west of Gopher Mountain, a dike 

of biotite granodiorite cuts the quartz diorite of the 

Duncan Hill pluton up to, but not beyond, the contact 

between the quartz diorite and the enclosing 

clinopyroxene-biotite-quartz schist; beyond the contact, 

a fracture continues in the schist along the projection of 

the dike. All these rocks, the quartz diorite, the dike, and 

the schist, have a parallel foliation.

Contacts with older rocks are either sharp or

1felfc*l*&i

** % 

^^

Jtitg-#* ^^

TipIlTplllflWlj

.,* * - *** ^.i *^ ^ 2

FIGURE 94. Biotite-quartz monzonite, north of Railroad Creek, 2 km 

east of Holden, Lucerne quadrangle.

gradational through a few centimeters; with the 

hornblende-biotite-quartz diorite, or Duncan Hill 

pluton, the contacts are commonly not only sharp but 

highly irregular, and near such contacts, inclusions of 

the older rock are numerous. Where the quartz 

monzonite-quartz diorite contact is exposed in the roadcut 1.5 km east of Holden, the quartz monzonite contains pyrite-bearing inclusions of hornblende gabbro of 

Riddle Peaks. The pyrite occurs along chlorite-filled 

fractures confined to the gabbro. The quartz monzonite 

adjacent to these inclusions is nearly devoid of mafic 

minerals, whereas the inclusions are bordered by 

selvages of biotite a fraction of a centimeter thick; some 

of these selvages are slickensided. The contacts of quartz 

monzonite and quartz diorite are mostly gradational 

through the space of a millimeter or two, but the quartz 

diorite is otherwise unaffected by the quartz monzonite. 

Dikes of biotite-quartz monzonite and granodiorite 

farthest from the main large mass on the east side of 

Wilson Creek are notable for their generally gradational 

contacts; these are best seen underground in the Holden 

mine. Here, many of these dikes are bordered by maficfree zones of quartz and feldspar, and in places these, in 

turn, are bordered by mafic-rich layers in the enclosing 

gneiss and schist that form a sort of "basic behind." 

Where these dikes are parallel to the foliation of the 

gneiss and schist, the contacts are generally sharper and 

the mafic-free borders are narrower than where dikes 

transgress the foliation. The contacts of transgressive 

dikes are extremely irregular, and felsic border material 

insinuates and replaces the foliated host rocks away from 

the dikes for varying distances along planes of foliation. 

Some dikes consist of little but felsic material and seem 

to have formed almost entirely by replacement. Many of 

these replacement dikes can be seen to emanate from 

dikes of biotite-quartz monzonite and granodiorite, and 

some, in fact, cut and replace the parent dikes. Of particular interest is the fact that in the Holden mine these 

dikes are postore inasmuch as they contain inclusions of 

the ore and in places seem to have remobilized the adjacent sulfides to a small extent. The sulfides form tiny 

veinlets in the otherwise completely fresh dikes that 

show no other sign of having been subjected to mineralizing solutions.

As seen in thin section, the biotite-quartz monzonite 

and granodiorite resemble the hornblende-biotite-quartz 

diorite, except for the relative abundance of potassium 

feldspar. Most of the plagioclase has an average composition of about An2 2, but locally the average composition of plagioclase is about An32. As with the quartz 

diorite, the range of composition within crystals is large, 

from An55 in the cores of some to Ani5 in some rims. 

Orthoclase, much of it perthitic, constitutes nearly 30 

percent of some specimens and occurs either interstitially or as a mesostasis that encloses and replaces
84 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

plagioclase. Myrmekite is common along borders 

between orthoclase and plagioclase. Quartz is interstitial 

or forms lenticular aggregates of interlocking, sutured 

grains. Biotite occurs as highly pleochroic (light straw 

yellow to dark muddy brown) ragged shreds. Primary 

muscovite was seen in a few thin sections, and relatively 

coarse secondary muscovite as blades 0.1 mm or more in 

length replaces plagioclase in most thin sections. 

Titanite, allanite, zircon, and apatite are accessory. 

Secondary minerals other than muscovite are chlorite, 

epidote, and pyrite.

Textures are either hypidiomorphic or, unlike 

horn blende-biotite-quartz diorite, protoclastic. The 

hypidiomorphic varieties commonly show flow-oriented 

features and are texturally identical to the quartz 

diorite. Plagioclase crystals of protoclastic rocks are 

broken and abraded, but most of the later minerals 

potassium feldspar, quartz, and biotite are undeformed, although scattered biotite flakes are bent.

Modal analyses indicate that variations in composition are relatively minor (table 35; fig. 95). Chemical and 

spectrographic analyses and norms are given in table 36, 

and the norms are plotted in figure 71.

POST-LATE EOCENE INTRUSIVE ROCKS

DIKES OF BIOTITE DACITE AND RHYODACITE

A few dikes of gray, fine-grained, slightly porphyritic 

dacite and rhyodacite that bear little resemblance to any 

other rock in the area cut the Railroad Creek pluton in 

the Riddle Creek drainage. None of the observed dikes 

are thicker than 3 m, and all strike northeast, or less 

commonly, nearly east. The rock consists of calcic 

andesine, quartz, biotite, and potassium feldspar; some 

of the dikes contain sufficient potassium feldspar to classify them as rhyodacite. Most of the rock consists of 

various intergrowths of plagioclase, quartz, and potassium feldspar; of the intergrowths, myrmekite is most 

abundant and forms a groundmass enclosing crystals of 

biotite and oscillatorily and patchy zoned andesine; the 

rest forms overgrowths around some andesine crystals. 

The plagioclase fraction of the myrmekitic overgrowths

is progressively zoned from oligoclase to albite, and some 

of the albite is antiperthitic. The more potassic rocks 

contain considerable granophyre, much of it also as 

overgrowths on andesine. Prehnite occurs in some of the 

dikes.

The age of these dikes is not known, except that they 

are younger than the Railroad Creek pluton. The pluton 

had cooled by the time the dikes were injected, and they 

possibly are as young as Miocene.

RHYODACITE

Dikes mapped as rhyodacite porphyry are numerous in 

the area between the Chiwaukum graben and Lake 

Chelan. Included in this class of rocks is an altered, 

porphyritic plug a few hundred meters across that cuts 

highly brecciated rocks of the Cardinal Peak pluton 

northeast of Milham Pass. The dikes range from several 

centimeters thick to one in the southwest corner of the 

Lucerne quadrangle that is more than 60 m thick. 

Strikes vary, but most trend either northeast, or more 

rarely, northwest. All are conspicuously porphyritic and 

light to medium gray or greenish gray; thinner ones have 

aphanitic groundmasses, whereas the thicker ones may 

be merely fine grained. These rhyodacite dikes rather 

closely resemble the younger dacite and the rhyodacite 

dikes which are more consistently characterized by 

quartz phenocrysts.

The composition of rocks mapped as rhyodacite ranges 

between rather wide limits; although by far the largest 

number of dikes are rhyodacite, some are dacite and 

others probably contain enough potassium feldspar to be 

classed as quartz latite. The ages of these dikes may 

cover a considerable span; although they cut late Eocene 

plutons, a minimum age cannot be established on 

geologic grounds.

Phenocrysts of plagioclase ranging in average composition from oligoclase (about An2e) to andesine (about 

An4.<0, biotite or hornblende and both in some rocks, and, 

less commonly, quartz are set in aphanitic to finegrained mats of plagioclase, quartz, biotite, hornblende, 

and orthoclase. Plagioclase phenocrysts show prominent

TABLE 35. Modal analyses of samples of biotite-quartz monzonite and granodiorite of post-late Eocene age, Holden and Lucerne quadrangles

Sample

No.

10

25

26

27

34

35

36

37

Plagioclase

53

43.9

31.6

47.9

41.4

35.1

25.9

34.8

Potassium

feldspar

7.6

11.1

27.2

11.1

19.6

26.5

22.1

26.3

Quartz

22.8

37.5

35.5

32.2

29.1

31.9

44.2

31.6

Biotite

15.4

4.0

1.5

7.9

9.6

2.4

1.6

6.9

Hornblende

0

2.5

2.4

0

0

.8

5.0

0

Accessory

and secondary minerals

0.9

1.0

1.8

.9

.3

3.3

1.0

.4

Total

mafic

minerals

16.3

7.5

5.7

8.8

9.9

6.5

7.6

7.3

Anorthite in

plagioclase crystals (percent)

Average

26

24

23

28

26

20

23

25

Core

41

26

29

33

40

22

27

30

Rim

20

21

19

15

18

18

21

17

Remarks

Protoclastic.

Porphyritic.

Xenomorphic.

Hypidiomorphic.

Subparallel andesine

laths; hypidiomorphic.

Hypidiomorphic.

Protoclastic.

Hypidiomorphic.
TERTIARY INTRUSIVE ROCKS 85

TABLE 36. Chemical and spectrographic analyses and norms of a 

composite sample of biotite-quartz monzonite, Holden and Lucerne 

quadrangles

[SiO2 and AhOs determined colorimetrically; Fe2O3, MgO, CaO, and MnO determined by 

atomic absorption; FeO determined volumetrically; Na2O and K2O determined by flame 

photometer. Analysts: Wayne Mountjoy, J. D. Mensik, Claude Huffman Jr., G. T. Burrow, 

and H. H. Lipp. Spectrographic analyses by Barbara Tobin]

Chemical analysis 

(percent)

Si02 --

A12 03 --

Tji f\

FeO---

MgO --

PaO

Na2 0--

K

/-\

MnO--

Total

HA C

00

1 98

0.9

....... 9 ft

3

T-1 A

3

OC

-------- .04

-------101

Se mi quan tit ati ve 

spectrographic 

analysis (parts per million)

Ba -------------700

/ i n

/-! 1-7

Cu------------- 3

Ga------------- 15

Ni ------------- 7

G,. n

Cr onn

V------------ - "V)

Y .............. 10

Yb------------- 1

Zn ------------- 70

Norms

q ...........

ah

hy .....-----

Total ------

- - 19.05

01 97

Q 01

9 8Q

2

OC

EC

inn nn

Plagioclase composition

9Q Q

oscillatory zoning, and patchy zoning is common; quartz 

phenocrysts are usually anhedral, but scattered, partly 

resorbed bipyramidal crystals occur. Granophyre is common in some dikes. Both hornblende and biotite are 

generally shredlike, but fine-grained aggregates of 

biotite or actinolite pseudomorphing euhedral hornblende crystals are numerous. A little augite was seen in 

a thin section from a dike on Crow Hill in the southeast 

corner of the Lucerne quadrangle. Mafic minerals show 

varying degrees of alteration to chlorite and, less commonly, nontronite; plagioclase, where altered, is saussuritized or sericitized.

The dacite porphyry plug northeast of Milham Pass is 

extensively altered, and outcrops are highly stained with 

limonite derived from disseminated iron sulfides, but no 

unoxidized sulfides or staining from oxidation of metallic minerals other than those of iron were seen. Even the 

freshest outcrops have largely disintegrated to a grus, 

and most are deeply weathered and rotten as attested by 

debris from a caved adit or two. Thin-section examination showed the freshest rock to consist of phenocrysts of 

labradorite, quartz, hornblende, and biotite in a finegrained groundmass of the same minerals plus their 

alteration products. The age of the plug is unknown but 

is almost certainly post-Eocene.

DACITE AND RHYODACITE DIKES

Dacite and rhyodacite dikes crop out in two general 

areas. In the drainage basin of Railroad Creek upstream 

from Holden, and in the southeastern part of the Holden 

quadrangle east of the Chiwaukum graben and adjacent 

parts of the Lucerne quadrangle. Because of their

,36

 34 26

.35,37

.10

5/ 

Piagioclase 35

Potassium

feldspar

FIGURE 95. Plot of modes of biotite-quartz monzonite and granodiorite samples from Holden and Lucerne quadrangles on a quartzpotassium feldspar-plagioclase diagram. Sample analyses are given 

in table 35.

similarity to various chilled phases of the Miocene 

Cloudy Pass batholith, the dikes were considered satellitic to the batholith as was the volcanic neck of Old Gib. 

A radiometric age of the Old Gib rocks determined by 

Joan Engels (Engels and others, 1976) indicates that 

these rocks are late Eocene and are of the same age as the 

Duncan Hill and other plutons of late Eocene age east of 

the Chiwaukum graben. Very likely the scattered dikes 

of dacite and rhyodacite in the Railroad Creek area are 

related to Cloudy Pass Rocks, but the affinities of those 

east of the Chiwaukum graben are much less certain. 

These dikes appear identical to the rocks of Old Gib, yet 

they cut the Larch Lakes and Rampart Mountain 

plutons, and the Duncan Hill pluton, which has the 

same radiometric age as the Old Gib volcanic neck. They 

also have chilled margins against the plutons through 

thousands of meters vertically. Obviously, these plutons 

had cooled before the dikes were intruded. Therefore, 

although they are indistinguishable from Old Gib rocks, 

it seems likely that the dikes are considerably younger 

and may, in fact, be related to the Cloudy Pass. In one or 

two localities among the dike swarms near Garland 

Peak, dacite and rhyodacite dikes were observed to cut 

rhyodacite dikes. Careful search, however, may discover 

opposite crosscutting relations. In any event, until the 

dikes east of the graben are dated radiometrically, little 

more definite age assignment than probable post Eocene 

seems justifiable.
86 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

MIOCENE INTRUSIVE ROCKS

Intrusive rocks of Miocene age comprise a number of 

plutons, stocks, and small plugs of different compositions, mostly in the Glacier Peak and Holden quadrangles, and great numbers of dikes, particularly in the 

Holden and Lucerne quadrangles. The diversity of rock 

types in each intrusive epoch during the Tertiary, combined with the similarity in appearance of rocks of 

similar composition, regardless of age, complicates the 

process of determining relationships. West of Garland 

Peak in the Lucerne quadrangle, a dike or two of 

rhyodacite porphyry was seen that was cut by dacite or 

rhyodacite containing prominent quartz phenocrysts. 

Both types of dikes cut plutons of known late Eocene age 

and have chilled margins against them through thousands of vertical meters. For this reason, these dikes are 

all thought to be appreciably younger than the plutons of 

late Eocene age and possibly as young as Miocene.

Most of the dacite and rhyodacite dikes strike 

northeast, but west of Rock Creek many strike northnorthwest parallel to both the regional trend of the 

metamorphic host rocks and the pervasive shear zones. 

Dacite and rhyodacite are indistinguishable in outcrop; 

both are light gray and conspicuously porphyritic, and in 

this respect are very similar to some of the rhyodacite 

dikes that are thought to be older; in fact, some dikes 

were probably misidentified because of similar outcrop 

appearance. Phenocrysts of plagioclase as much as 5 mm 

across and of quartz, biotite, and more rarely hornblende 

as much as 3 mm in greatest dimension are scattered 

through an aphanitic to fine-grained, light-gray groundmass. Thin dikes are aphanitic throughout but only the 

chilled margins of the thicker dikes are aphanitic. 

Plagioclase phenocrysts in both dacite and rhyodacite 

are high-temperature andesine, showing numerous oscillatory zones in addition to patchy zoning; the average 

composition of plagioclase in most sections is about Ans2 , 

but in some is as calcic as An. . Most quartz phenocrysts 

are rounded and resorbed, but a few are euhedral 

bipyramids. Biotite and hornblende occur as euhedral to 

anhedral grains; hornblende commonly shows some 

replacement by biotite, and both are variously replaced 

by chlorite. The groundmass consists of an equigranular, 

interlocking mosaic of oligoclase, quartz, and biotite in 

all the dikes, plus hornblende in some. Rhyodacite differs from dacite only in its higher content of orthoclase; a 

few dikes also contain a little microcline. Some 

granophyre occurs in the groundmass of scattered dikes 

of both dacite and rhyodacite. Rather characteristically, 

phenocrysts of plagioclase and quartz have corroded 

margins of moth-eaten appearance suggestive of resorption by the groundmass. Some dikes intruded along 

shear zones have been intensively sheared since 

emplacement so that phenocrysts appear as augen in a 

finely comminuted groundmass.

CLOUDY PASS BATHOLITH AND RELATED ROCKS

Youngest of the major intrusions in the area is the 

early Miocene Cloudy Pass batholith and its satellitic intrusive breccias, plugs, and stocks. The batholith is now 

being deroofed, and about 80 km2 of it are either exposed 

or covered by surficial debris in the northern parts of the 

Glacier Peak and Holden quadrangles. Adjacent parts of 

the mass lie under a relatively thin cover of metamorphic 

roof rocks. The part of the batholith lying within the 

Glacier Peak quadrangle has been described in detail by 

Tabor and Crowder (1969) and that in the Holden 

quadrangle by Cater (1969). Grant (1966; 1969, p. 30-34) 

and Tabor (1963) reported on the part cropping out 

north of these two quadrangles. The following description mostly summarizes the reports by Tabor, Crowder, 

and Cater.

The Cloudy Pass batholith is a discordant intrusion 

characterized by a wide variety of rocks and a 

remarkable array of subvolcanic features, including a 

complex of chilled border rocks along its northeast contact called the complex of Hart Lake (Cater, 1969, p. 

8-17). A belt of plugs and small stocks of Cloudy Pass 

rocks associated with a zone of thermally metamorphosed gneisses strongly suggest that a southwesterly 

trending nose of the batholith lies at rather shallow 

depths, and a southeasterly trending line of satellitic 

porphyry plugs and intrusive breccia suggests a similar 

nose beneath Phelps Ridge.

Contacts, except for those with flat-lying roof rocks, 

are steep to vertical. The nature of the contact, however, 

is variable depending on whether border rocks are chilled 

and whether the contact truncates foliation planes of the 

host rocks or is conformable. In the large areas where the 

margins of the batholith consist of chilled porphyritic 

rocks, the host rocks are crumpled and brecciated, but 

where the core of the batholith has cut through the 

chilled border rocks, or where they do not exist, the host 

rocks are hornfelsed or granitized in a narrow zone. 

Where the batholithic contacts are strongly discordant 

and chilled border rocks are absent, the enclosing gneiss 

was subject to considerable diking, stoping, and 

migmatization.

Most of the batholith consists of light-gray, mediumgrained, massive rock ranging in composition from 

quartz gabbro to granodiorite; of the various rock types 

granodiorite is most abundant, and most of this is 

labradorite granodiorite (granogabbro). Scattered 

through these similar-appearing main-facies rocks are 

masses of light-colored rocks, the largest mass of which 

caps the western part of the batholith on and in the 

vicinity of Miners Ridge. Contacts between contrasting 

rock types are gradational in most places, but on the 

north flank of the North Star Mountain the contact 

between normal and light-colored facies consists of a 

marble-cake mixture of the two.
TERTIARY INTRUSIVE ROCKS 87

Granodiorite and quartz gabbro are mostly structureless, but near some contacts a vague layering of 

lighter and darker rocks is visible that roughly parallels 

the contact. Lineation defined by alined hornblende 

crystals occurs locally. Inclusions of chilled border rocks 

and gneiss in various stages of assimilation are fairly well 

restricted to the uppermost parts of the batholith where 

they are locally abundant. Granodiorite consists of 

euhedral oscillatorily and patchy-zoned plagioclase, 

quartz, biotite, and hornblende; orthoclase, some of it 

microperthitic, is a major but quantitatively variable 

constituent. Quartz diorite and quartz gabbro differ 

from granodiorite only in the content of orthoclase and in 

these rocks it is generally absent. Clinopyroxene and 

hypersthene are rare except in the small intrusions in the 

Glacier Peak quadrangle and tend to occur only in the 

more rapidly cooled rock; both minerals are generally 

rimmed by uralitic hornblende. Plagioclase generally 

has an overall composition of sodic labradorite, but 

westward in the Glacier Peak quadrangle it tends to be 

more sodic and is mostly andesine. Quartz occurs both as 

partly resorbed euhedral crystals and as irregular grains 

with orthoclase as a mesostasis engulfing all earlier 

formed minerals. Orthoclase is invariably late and is of 

erratic distribution and abundance. All the orthoclase 

seems to be of metasomatic origin.

Light-colored facies are of two types, an oligoclasebearing granophyre and a metasomatized quartz gabbro 

or labradorite granodiorite. In the Holden quadrangle, 

the metasomatized rock containing labradorite is most 

prevalent and occurs as irregular masses apparently associated with zones of brecciation that formed in the 

cooling batholith. The rock has a psuedoporphyritic texture; larger crystals of labradorite and quartz are 

engulfed in and partly replaced by a xenomorphic aggregate of fine-grained quartz, albite-oligoclase, and 

orthoclase. Mafic minerals not replaced by this felsic 

material are mostly altered to chlorite. Much of the 

megacrystic labradorite has been fractured and the 

resulting crystal fragments slightly rotated with respect 

to each other; fractures are healed by veinlets of albite. 

The granophyric rock much resembles the metasomatized labradorite-bearing light-colored rock 

megascopically; but the mode of occurrence is generally 

different, particularly in the Holden quadrangle. Here 

the granophyre forms either dikes or the matrix of intrusive breccia, but in the Glacier Peak quadrangle 

where light-colored rocks are far more abundant, the 

granophyre forms much of the western part of the 

batholith. Most of the plagioclase in the granophyre is 

euhedral and oscillatorily zoned, but some of the most 

sodic plagioclase is interstitial. Compositions range 

widely; cores of scattered crystals are as calcic as Anss, 

but cores of most crystals are no more calcic than An3 o, 

and the groundmass is highly granophyric. Sparse

biotite is mostly altered to chlorite. Miarolitic cavities 

containing drusy quartz and a little pyrite are common 

in the granophyre. Modal data of Cloudy Pass rocks are 

given in table 37 and figure 97. Figure 96 is a map showing the location of the modally analyzed specimens.

Our views concerning the origin of these rocks differ 

somewhat. Tabor and Crowder (1969, p. 9-10) contended 

that all the "light-colored rocks formed by normal 

magmatic differentiation, not by replacement of an 

earlier formed phase by introduced residual solutions." 

They based their contention on the similarity in composition of the light-colored rocks to the composition of 

rocks in the area of the minimum melting trough of 

Tuttle and Bowen (1958, p. 55), and believed that the 

composition of these rocks is rather limited, which 

"would be unlikely if replacement by residual solution 

had been significant." I (Cater, 1969, p. 9-10) agree that 

the granophyre is an end product of normal differentiation, albeit a wet one; but I think that the labradoritebearing, light-colored rock formed as solutions rich in 

alkalies and silica partly replaced quartz gabbro. I base 

my view on the fact that in the Holden quadrangle, all 

gradations from quartz gabbro through granodiorite to 

the light rock exist, yet the core of all plagioclase is 

labradorite, and the light rock was shattered prior to 

replacement, thereby aiding transmission of fluids. In 

any event, addition of alkalies and silica to quartz gabbro would change the composition of the rock toward the 

minimum melting trough.

CHILLED BORDER ROCKS

Chilled porphyritic rocks occur at many places along 

the contacts of the Cloudy Pass batholith, and somewhat 

similar chilled rocks from the Tatoosh pluton in Mount 

Rainier National Park have been described by Fiske, 

Hopson, and Waters (1963). Most spectacular of the 

chilled rocks associated with the Cloudy Pass are those 

in the vicinity of Hart Lake. Here a chilled complex consisting of separately injected, contrasting layers of 

porphyry, having a thickness of more than 1 km, borders 

the northeast side of the batholith. Oldest is an outer 

layer of dacite porphyry that north of the complex grades 

directly into the core of the batholith, and south of Hart 

Lake diverges from the batholith as a prong. Next oldest 

is an inner layer of dacite and labradorite-bytownite 

andesite, and in the middle, a still younger layer of 

autobreccia of a composition similar to that of the inner 

layer. The inner layer extends from Hart Lake north to 

the head of Glacier Creek, but neither end of the layer is 

exposed. Where the contact of the inner layer and the 

core of the batholith is visible, the core intrudes or cuts 

the inner layer, but the amount of movement by the core 

magma could not have been great because north of the 

pinchout of the inner layers, the outer layer grades into
INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

TABLE 37. Modal analyses of samples of granodiorite from the Cloudy Pass batholith, Holden quadrangle

Sample

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

48°

15'

{

Potassium

Plagioclase

47.4

48.3

45.4

60.6

33.4

55.0

25.6

51.5

49.3

48.8

46.2

37.0

49.7

49.8

46.3

57.3

41.0

50.8

30.4

30.4

50.5

42.3

45.2

46.0

AT3

k^

feldspar

21.8

3.4

12.8

4.9

13.0

1.4

31.8

12.6

5.6

5.6

6.3

18.3

15.7

10.3

2.6

6.1

16.6

12.0

27.6

27.5

15.0

18.9

13.9

.5

121 C

-~~__ -

<

Q

rD

o

<

C£

V- "~~<

CO

0

Quartz

26.8

14.1

26.1

24.2

28.7

28.7

35.6

21.1

20.2

26.9

28.4

23.6

16.2

23.6

23.5

13.4

26.1

25.4

34.3

35.1

23.1

23.8

22.4

16.0

Biotite Hornblende

3.0

11.2

9.3

7.3

18.9

10.8

1.5

7.3

7.3

7.4

8.0

11.1

8.4

7.1

22.3

9.3

3.3

2.1

2.5

1.4

6.6

10.3

5.2

18.3

0

17.7

5.2

0

4.2

2.6

0

5.0

12.1

11.0

3.1

4.3

5.9

7.0

4.2

8.7

5.2

7.5

0

0

4.4

3.6

12.3

17.7

Accessory Total

and second- mafic

ary minerals minerals

1.0 4.0

5.3 34.2

1.2 15.7

3.0 10.3

2.8 25.9

2.5 15.9

5.5 7.0

2.5 14.8

5.5 24.9

.3 18.7

3.0 19.1

5.7 21.1

4.1 18.4

2.2 16.3

1.1 27.6

5.2 23.2

7.8 16.3

2.2 11.8

5.2 7.7

5.6 7.0

.4 11.4

1.1 15.0

1.0 18.5

1.5 37.5

00'

s»i

ml_3 < ^D\^^^^^

o

<

= 22.

LLJ 01

a * ' 

o\-_ ° ^~\-

 '2.

 3 

5

t.6

'13 '

 23 \^J'^~~

4\

.7 \

 8\ 

9. S

} * .15 '16

*

.18 /

V /

1 2°"^

24. /

vJx

>>

5 KILOMETERS

i i i I

Anorthite in

plagioclase crystals (percent)

Average

55

52

53

54

50

54

35

54

50

53

50

53

51

50

54

51

51

50

44

52

50

52

53

53

Core

69

54

55

63

58

62

51

63

61

67

67

58

54

55

61

54

56

0

56

44

61

55

64

0

/

Rim

34

32

32

33

25

25

18

29

26

27

38

40

24

11

18

0

9

0

22

22

31

24

29

0

/

/ 

Remarks

Porphyritic.

Slightly porphyritic.

Hypidiomorphic.

Prophyritic-protoclastic .

Hypidiomorphic.

Porphyritic.

Do.

Hypidiomorphic.

Do.

Do.

Do.

Do.

Do.

Do.

Do.

Contains augite.

Slightly porphyritic.

Contains a little

augite.

Porphyritic.

Reversed zoning of

plagioclase; porphyritic.

Hypidiomorphic; a

little augite.

Hypidiomorphic .

Do.

Porphyritic.

Quartz

/ / '''

// '

// 1

/ /

/ / ' BO/-/ r

*17

.5 20. .7

.11 19

*10

18 » i .12

FIGURE 96. Map showing locations of modally analyzed samples of 

granodiorite from the Cloudy Pass batholith, Holden quadrangle. 

Sample analyses are given in table 37.

the core with no evidence of disturbance. The middle 

layer is more complex and consists of dacite and andesite 

autobreccia and resembles a volcanic flow breccia in appearance. The contact with the inner layer is 

gradational, but the contact with the outer layer is intrusive. This intrusive contact, however, is evident only 

at higher altitudes where the outer layer had solidified 

before intrusion of the middle layer. At lower altitudes 

near Hart Lake, the contact with the outer layer is partly 

gradational and partly mixed as though the outer layer 

were still plastic when the middle layer was injected. 

The dacite porphyry of the outer layer consists of

Plagiociase

Potassium 

feldspar

FIGURE 97. Plot of modes of samples from the Cloudy Pass batholith, 

Holden quadrangle, on a quartz-potassium feldspar-plagioclase diagram. Sample analyses are given in table 37.

phenocrysts of sodic labradorite, quartz, hornblende, 

and sparse augite in a fine-grained matrix of andesine, 

quartz, hornblende, biotite, chlorite, a little orthoclase,
TERTIARY INTRUSIVE ROCKS

and in some rocks, nontronite. Porphyries of the inner 

layer are dark gray to black and consist of intermixed 

andesite and dacite porphyry. The dacite is similar to 

the dacite of the outer layer; the andesite contains 

phenocrysts of labradorite-bytownite and hornblende in 

a groundmass of andesine, hornblende, biotite, and 

sparse quartz. Dacite and andesite of the middle layer 

are similar to those in the inner layer but are more highly 

altered, and fracture surfaces are coated with pyrite and 

pyrrhotite. At higher levels, chalcopyrite also becomes 

fairly common, and alteration is more severe.

Both porphyry plugs of various sizes and intrusive 

breccia puncture metamorphic rocks adjacent to the 

batholith; a few scattered pipes of intrusive breccia also 

cut the batholith. The plugs consist of dacite porphyry 

and, although somewhat more siliceous, are petrographically indistinguishable from dacite in the chilled 

borders. Intrusive breccias are of two types: one consists 

entirely of batholithic rocks and is confined to the pipes 

that cut the batholith; the other type cuts the 

metamorphic rocks and consists of varying proportions 

of both batholithic rocks and shattered fragments of the 

host rocks. This latter type is most common around the 

porphyry plugs and many of these breccia masses seem 

to have been injected explosively in a manner probably 

similar to fluidization processes as elucidated by 

Reynolds (1954). Breccia confined to the batholith consists of rounded fragments of both batholithic core rocks 

and chilled rocks contained in matrices of calcic quartz 

diorite and white quartz monzonite; the rocks in this 

type of breccia are unaltered. Rocks in breccias cutting 

metamorphic rocks, on the other hand, commonly show 

varying degrees of alteration, and some contain considerable amounts of sulfides, mostly pyrite and pyrrhotite but, locally, a little chalcopyrite and sphalerite.

The Cloudy Pass batholith, at least to the depth 

presently exposed, appears to have made room for itself 

mostly by lifting its roof. The discordant irregular shape 

of the batholith, plus the lack of any evidence for 

shouldering aside of the wall rock, lends strong support 

to this hypothesis, an hypothesis appropriate to a 

batholith at such shallow depths. The chilled complex at 

Hart Lake formed along the zone of dislocation where 

the host rocks in the roof of the batholith rose past those 

on the northeast flank. Along this zone of dislocation, the 

outer layer of the complex was injected as a dike ahead of 

and above the rising batholith. The inner and middle 

layers of the complex rose along this same zone of dislocation; the core of the batholith apparently continued 

rising somewhat after the inner layer had solidified at 

least to the depths presently exposed. Cooling by conduction seems to be totally inadequate to explain the 

rapid and uniform chilling of these two thick layers, particularly when the evidence indicates they were intruded 

between the still hot rocks of the outer layer and the still

fluid rocks of the batholithic core. The only process adequate to explain such rapid and uniform chilling of so 

large a mass of magma in such an environment is the 

refrigerating effect of expanding gases expelled from the 

large reservoir of magma at depth (Cater, 1969, p. 48). As 

freezing by degassing progressed, the breccia probably 

formed as partly solidified rock adjacent to channels of 

most vigorous gas flow and mixed with the more molten 

fractions as new magma was added from below. The 

more highly altered and fractured nature of these rocks 

and the presence of sulfides lend indirect support to the 

supposition that these layers and particularly the middle 

layer did indeed serve as escape routes for volatiles.

A number of marked differences exist between rocks in 

the upper parts of the Cloudy Pass and Duncan Hill 

masses; however, rocks in the upper part of the Duncan 

Hill pluton are highly miarolytic, suggestive of abundant 

water, and strikingly granophyric in contrast to rocks in 

the upper part of the Cloudy Pass. Plagioclase in even 

the most potassic of the main-facies rocks in the upper 

part of the Cloudy Pass mass, furthermore, is identical 

to the plagioclase elsewhere in the main body of the intrusive and shows extensive oscillatory and patchy zoning. Plagioclase in the upper part of the Duncan Hill 

pluton shows virtually no zoning, except progressive, 

and lacks the rather highly calcic cores characteristic of 

plagioclase elsewhere in the pluton. Compositions of the 

hypabyssal rocks in the Duncan Hill pluton are 

remarkably uniform; those in the Cloudy Pass batholith 

vary greatly over short distances. Rocks in the upper 

part of the Cloudy Pass seem to have been converted to 

more alkalic varieties by alkali-rich solutions passing 

through them after they had largely solidified, whereas 

the alkalic rocks of the Stormy Mountain area in the 

Duncan Hill pluton show no evidence of a similar conversion after solidifying and seem to have crystallized 

directly from a completely liquid, alkalic magma.

LEUCOCRATIC BIOTITE-QUARTZ MONZONITE

About 1.5 km south-southwest of Mirror Lake in the 

Lucerne quadrangle, a mass of leucocratic biotite-quartz 

monzonite, having an exposed length of about 1 km, 

crops out west of Tumble Creek. The rock is medium 

grained and massive and on fresh surfaces is nearly 

white, but because it disintegrates and weathers rapidly, 

outcrops are limonite stained and deeply rotted. Contacts with the enclosing quartz diorite gneiss of the Bearcat Ridge pluton are knife sharp where observed.

The leucocratic biotite-quartz monzonite consists of 

40 to 45 percent quartz, 30 to 35 percent oligoclase, 20 to 

25 percent perthite, and less than 3 percent accessory 

biotite, magnetite, and zircon; small amounts of sericite, 

epidote, and pyrite are secondary. Oligoclase occurs as 

subhedral to euhedral crystals having an average composition of about An2 4; oscillatory and patchy zoning
90 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASfflNGTON

show in most crystals, and some have rims of normally 

zoned material grading into albite on the outer edge. 

Quartz either forms irregular grains that replace 

oligoclase, or it occurs interstitially; most of it is 

strained. Irregular grains of perthite are as much as 8 

mm across and it replaces both oligoclase and quartz. Irregular shreds of biotite as much as 3 mm across are 

pleochroic from light yellowish brown to dark muddy 

brown. Zircon occurs only as minute grains in biotite 

where it forms pleochroic halos. Magnetite most commonly forms lenticular grains wedging apart cleavage 

flakes of biotite. Pyrite occurs as fine dust along grain 

borders and in altered cores of oligoclase or as larger 

grains along fractures. The more calcic cores of oligoclase 

are partly altered to sericite and epidote. The texture is 

hypidiomorphic but shows protoclastic modifications; 

some grain borders are granulated but are healed by 

quartz and perthite.

The age of the leucocratic biotite-quartz monzonite is 

uncertain; it does, however, cut the Bearcat Ridge 

pluton and, hence, is younger. It resembles no other rock 

seen in the area, but its texture and appearance are those 

of a shallow intrusive, and no dikes were seen to cut it. 

On no really sound evidence, I believe it to be younger 

than the Eocene intrusives possibly as young as 

Miocene.

CONTACT COMPLEXES

The contact complexes associated with the Sevenfingered Jack, White Mountain, Cardinal Peak, Duncan 

Hill, Holden Lake, and Copper Peak plutons in the 

Holden and Lucerne quadrangles, and the Tenpeak and 

Sulphur Mountain plutons in the Glacier Peak 

quadrangle (Crowder, Tabor, and Ford, 1966) are the 

most heterogeneous and perplexing intrusive rocks in the 

area. All consist of extremely diverse mixtures of rocks 

that differ little in overall characteristics from one 

pluton to another. All are composed of mixtures of coarse 

hornblendite, gabbro, diorite, quartz diorite, and inclusions in various stages of digestion or incorporation. The 

igneous fractions of these complexes rocks as divergent 

as gabbro and quartz diorite appear to have been 

simultaneously molten. Mixtures of these rocks range 

from those resembling marble cake, where contacts 

between different rock types are sharp, to rare, 

thoroughly homogenized hybrid rocks containing both 

calcic and sodic plagioclase that resemble the mixed 

magmas described by Larsen and others (1938). 

Probably these complexes most nearly resemble appinite, a group of rocks of highly variable composition 

but characterized by much coarse-grained hornblendite 

and gabbro or peridotite (Bailey and Maufe, 1960, p. 

190-194, 214-215; Bowes and others, 1964; Hall, 1967;

Pitcher and Berger, 1972). The contact complexes differ 

from the appinites, however, in nowhere forming discrete 

intrusives disconnected from a parent pluton.

The distribution of the complexes tends to be 

somewhat erratic and spotty. The contact complex of the 

White Mountain pluton, for example, is virtually confined to the crosscutting north end of the mass, whereas 

the complexes of the other plutons also occur along concordant margins, and in the Seven-fingered Jack 

plutons, rocks identical to the complexes also occupy internal positions. The contact complexes associated with 

the Tertiary Duncan Hill pluton are confined to the 

mesozonal north end, whereas complexes rim a good part 

of the Holden Lake and Copper Peak intrusives.

The origin of these contact complexes is obscure. With 

the exception of the quartz gabbro Holden Lake and 

Copper Peak plutons, the complexes seem to be confined 

to mesozonal plutons or, in the Duncan Hill, to the 

mesozonal end of the pluton. The cores of the plutons cut 

the complexes, but generally the complexes seem not to 

have been solidified when they were invaded by the 

cores. The diorite and quartz diorite in the complexes are 

sufficiently similar in composition to the core rocks to 

have been derived directly from them, but this 

relationship cannot be true for the ubiquitous hornblende gabbro or coarse-grained, generally pegmatitic 

hornblendite, the rocks most characteristic of the complexes. The unhomogenized marble-cake mixtures of 

gabbros and siliceous igneous rocks would suggest such 

mixtures are not far traveled, and the presence of both 

calcic and sodic plagioclase in homogenized hybrid rock 

indicates that their disequilibrium sojourn in the mixed 

magma before solidifying could not have been prolonged. 

Sodic rims on labradorite commonly are broader in the 

hybrid rocks than on labradorite in normal hornblende 

gabbro, however. Intimate associations of mafic and 

felsic rocks in various intrusive and extrusive masses 

have been described repeatedly, more recently by 

Walker and Skelhorn (1966) and Blake and others 

(1965). These authors reached the conclusion that 

separate and probably unrelated magmas were involved 

that by one means or another utilized the same plumbing systems simultaneously in their rise through the 

Earth's crust. It seems entirely likely that the same circumstances prevailed in the formation of these contact 

complexes. Possibly small quantities of hornblende gabbro magma lower in the crust or upper mantle were 

forced up along the same channels and at the same time 

as much larger quantities of more felsic magma from 

somewhat higher but still low in the crust. Yoder (1973) 

postulated that small batches of contrasting magmas are 

melted as a result of adiabatic decompression, and each 

magma is extracted at separate invariant points. The 

melting temperatures of gabbroic or basaltic magmas
GENERAL GEOLOGICAL PROBLEMS RELATING TO INTRUSIVE ROCKS 91

are 100°-200° C higher than are those of siliceous 

magmas (Yoder and Tilley, 1962), and the mixing ofgabbroic magma from probably deeper in the crust would 

raise the temperature of the siliceous magma in the contact complexes. In a few outcrops, the gabbro adjacent to 

quartz diorite is finer grained as though it had been 

chilled against quartz diorite (fig. 33). Perhaps the 

higher temperatures and consequent greater mobility of 

the mixed magmas of the complexes accounts for the 

greater number of wall-rock inclusions and the more 

highly modified nature of wall rocks adjacent to the complexes than where core rocks of the pluton are in direct 

contact with the host rocks.

The hornblende gabbro of Riddle Peaks at least 

demonstrates that a sizeable reservoir of gabbroic 

magma existed at one time in the area; furthermore, this 

gabbro is nearly identical to most of that occurring in the 

contact complexes. Such magma then could have used 

conduits that subsequently were used by quartz diorite 

magma from a different source. The possibility exists, 

nonetheless, that hornblende gabbro in the contact complexes is a differentiate from a parent magma of the 

diorite and quartz diorite, although the evidence does 

not lend a great deal of support to the existence of a 

comagmatic series of gabbro and quartz diorite. To test 

the possibility that the gabbro and quartz diorite had 

different lineages, gabbro and quartz diorite from intrusive complexes associated with the Seven-fingered 

Jack plutons were analyzed for initial strontium isotopic 

ratios (Zell Peterman, written commun., 1975). The 

results are shown in table 38.

The initial strontium isotope ratios are low, comparable to those of Cascade Range volcanic rocks 

(Peterman and others, 1970) and are suggestive of a 

source in the upper mantle. The agreement of ratios for 

gabbro and quartz diorite neither proves nor disproves a 

genetic relationship between the two rocks, but an 

anatectic origin from crustal rocks does seem to be 

precluded.

GENERAL GEOLOGIC PROBLEMS 

RELATING TO THE INTRUSIVE ROCKS

Discussion of problems relating to compositional and 

mineralogical variations, differentiation, and emplacement of the intrusive rocks of the area is complicated by 

the fact that the intrusions in the northern Cascades are 

perhaps the most diverse group of Phanerozoic plutons 

in the entire country. In composition, they range from 

ultramafic to granite, a range that may be present 

elsewhere, but in one important aspect they are 

unique the range of depths to which they are exposed. 

Within the confines of single 15-minute quadrangles are

exposed plutons ranging from those having subvolcanic 

features to those of the catazone. For more than 200 

m.y., or since the accretion of the microcontinent of 

Cascadia to the North American continent (Davis and 

others, 1978, p. 15), the region has been the scene not 

only of continuous tectonic activity but of intermittent, 

if not continuous, intrusive activity (Yeats and Engels, 

1971), and if the present volcanoes are any criterion, 

magma is still being pumped into and through upper 

crustal rocks. Gilluly (1973, p. 503-505) has pointed out 

that in the Cordillera, as a whole, magmatism has been 

continuous since early Mesozoic time and that "there is 

no sign whatever of any periodicity," and Silberman and 

McKee (1971, p. 20) concluded that only in areas smaller 

than 50,000 km2 does plutonism seem to be episodic. The 

conclusion of Yeats and Engels (1971, p. D38) that there 

was no evidence of plutonism in the northern Cascades 

between about 48 to 90 m.y. ago has been refuted by 

later work (Engels and others, 1976).

The older intrusives, such as the Dumbell Mountain 

plutons, have been carved to levels many kilometers 

deep, whereas the youngest, such as the Cloudy Pass 

batholith, are only now being deroofed. Study of intrusive rocks in such a terrane tends to enfeeble ones 

faith in the validity of such terms as "post-" and 

"synkinematic" or "post-" and "syntectonic," when applied to intrusive granitoid rocks. Such faith can 

degenerate into outright skepticism when one views a 

pluton, such as the Duncan Hill, which is synkinematic 

on one end, the deep one, and postkinematic on the other 

or shallow end and this in an area where tectonism is 

still progressing at a rate probably as lively as ever. Buddington (1959, p. 731) has pointed out that epizonal 

plutons are posttectonic, mesozonal plutons are either 

post- or occasionally late- kinematic, and catazonal 

plutons are syntectonic and synkinematic. Most likely, 

all postkinematic plutons are synkinematic at depth.

The plutons making up great composite batholiths 

such as the Idaho, the Sierra Nevada, or the Southern 

California seem to possess a common heritage; the 

plutons of the northern Cascades lack this overall unity. 

Only the most intrepid would genetically relate the 

Dumbell Mountain plutons to the 200-m.y.-younger 

Cloudy Pass batholith, for example. The more or less 

systematic chemical changes that correlate roughly with 

the order of emplacement of plutons in the great 

batholiths are largely lacking in the northern Cascades, 

although single, moderate-size batholiths such as the 

Snoqualmie (Erikson, 1969) and the groups of plutons of 

approximately the same age, do have such features. 

Nevertheless, certain broad characteristics do seem to 

vary with time of emplacement, but these variations appear to be related more to the level of exposure than to 

close genetic ties.
92 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASfflNGTON

TABLE 38. Initial strontium isotope ratios of gabbro and quartz 

diorite from intrusive complexes associated with the Seven-fingered 

Jack plutons, Holden quadrangle

[Analysts: Sr87/Sr86 , K. Futa (chemistry) and R. Hildreth (mass spectrometry), Rb and Sr 

concentrations: W. Doering (by X-ray analysis). Analytical uncertainties: Sr "/Sr": 

±0.002 (2 sigma). Concentrations: ±5 percent of values]

Rock type Rb(ppm) Sr(ppm) Rb/Sr Sr'VSr86 (Sr"/Sr")0

Quartz diorite-- 52.9 556 0.095 0.7042 0.7040

Gabbro-------- 7.2 395 .018 .7037 .7037

'Initial Sr^/Sr84 corrected for in-situ growth of radiogenic Sr87 for 64 m.y.

RELATION OF INTRUSIVES TO HOST ROCKS 

AND THE ROOM PROBLEM

All the major intrusives in the study area reflect some 

degree of structural control, but such control is more 

pronounced in the older plutons. The older plutons are 

elongate and relatively concordant, whereas the younger 

ones tend to be areally more nearly equidimensional but 

irregular in outline and show less influences by structure 

of enclosing rocks. Even the youngest major intrusive in 

the area, the Cloudy Pass batholith, however, has a 

northeast contact that parallels the trend of the wall 

rock of gneissic quartz diorite of Dumbell Mountain.

Both faults and structural trends of the metamorphic 

country rocks influenced the form of various major 

plutons, but faulting seems to have had controlling influence only on the Seven-fingered Jack and less certainly on the Dumbell Mountain and High Pass plutons. 

The almost dikelike Seven-fingered Jack plutons are 

strongly controlled by the ancient fault system later 

reactivated and bounding the northeast side of the 

Chiwaukum graben; the equally elongate but much 

older Dumbell Mountain plutons possibly may have 

been injected along early dislocations in this same fault 

system. The relation of the High Pass pluton to enclosing 

rocks is much more complex than are relations to host 

rocks of other plutons in the area. The High Pass pluton 

is a thick, low-dipping sheet that truncates a synform of 

upper Paleozoic metasedimentary rocks at a low angle; 

much of the pluton is sill-like, but the narrow, 

southeasterly part of the mass cuts across the synform, 

and in the valley of Alpine Creek, it occupies the crest of 

a small antiform. Two separate bodies of probable High 

Pass rocks to the northeast, called the Buck Creek 

plutons of the main mass have intruded the contact 

between the Paleozoic metasedimentary rocks and the 

lower Paleozoic or older Swakane Biotite Gneiss. The 

contact may be a thrust plane because the structural 

relations between the metasediments and the Swakane 

strongly suggest that the metasediments were thrust 

over the Swakane much in the manner of a tractor

tread before the sediments were metamorphosed to 

amphibolite grade.

Plutons where the only apparent structural influence 

seems restricted to the attitude of enclosing rocks range 

from those showing a close adherence to trends of the 

host rocks throughout their lengths, as does the Duncan 

Hill, to those that are largely discordant but have some 

contacts that are concordant for considerable distances, 

as illustrated by the Clark Mountain stocks. The 

Duncan Hill, Cardinal Peak, and to only a slightly less 

degree the Bearcat Ridge plutons, virtually parallel the 

strike of the enclosing metamorphic rocks or diverge but 

little throughout their mapped lengths. The parallelism 

of these plutons to the host rocks, however, is restricted 

to strike; downdips all are crosscutting. The Cardinal 

Peak pluton cuts a large, southeast-plunging, overturned 

antiform; the Bearcat Ridge plutons dip more nearly 

conformable to but do cut the host rocks at low angles, 

and the vertically dipping Duncan Hill pluton transects 

the moderate to steeply dipping host rocks downdip. 

Within the mapped area, the Tenpeak pluton is essentially a thick sill. Only the north end of the elongate oval 

White Mountain pluton crops out in the mapped area, 

and here it replaces a considerable thickness of 

metasediments. To the south, the contacts of the White 

Mountain that were examined are concordant. The gabbro of Riddle Peaks is cut off by later intrusives, but the 

screens of gneiss that in many places parallel the layering in the gabbro at least suggest that it too had strong 

structural control.

With the exception of the Duncan Hill pluton, the 

forms of the larger Tertiary intrusives were notably less 

subject to control by the structure of host rocks than 

were pre-Tertiary plutons, and the smaller intrusives, 

such as those of hornblende-biotite-quartz diorite and 

biotite-quartz monzonite, seem unshaped by obvious 

structures. The Cloudy Pass batholith and the sizeable 

Railroad Creek pluton both replace large thicknesses of 

host rocks of various kinds, but the northeast contacts of 

both are more or less concordant. The tadpole-shaped 

Duncan Hill pluton, however, is unique in that here in a 

single pluton is illustrated well the progression from 

strongly concordant relations to discordant relations to 

host rocks that otherwise is seen only in a succession of 

different plutons. The mesozonal, thin tail part of the 

pluton at the northwest end shows a degree of structural 

control comparable to that of most of the pre-Tertiary 

plutons, whereas the relatively thick hypabyssal head 

part of the mass is structurally similar to the Cloudy 

Pass batholith and cuts out large thicknesses of host 

rocks.

The assumption that batholiths widen downward and 

extend to great depth has been challenged by a number 

of geologists, including Cloos (1923), Chamberlin and 

Link (1927), Land (1931), and more recently, by
GENERAL GEOLOGICAL PROBLEMS RELATING TO INTRUSIVE ROCKS 93

Hamilton and Myers (1967). Moehlman (1948) has noted 

that Tertiary plutons in the southwest narrow 

downward. These authors argued variants of the theme 

that batholiths are floored, rather thin masses that may 

be completely detached from their sources in the upper 

mantle and lower crust because semiplastic wall rock, at 

depth, flowed downward and inward as buoyant masses 

of magma rose. Seismic and gravity data, such as exist 

for the Sierra Nevada batholith and summarized by 

Hamilton and Myers (1967, p. C3-C5), do not exist for 

the plutons in this study area, but the geologic relations 

do suggest the behavior of the plutons here was much the 

same as that of the Sierra Nevada. The youngest major 

intrusive, the Cloudy Pass batholith, and the nearby 

Snoqualmie batholith are only now becoming unroofed 

but have wide lateral extents and show none of the 

dikelike tendencies prevalent in the older, more deeply 

eroded masses. The outline of the Duncan Hill pluton indicates only an upward widening of the mass, but the 

lack of extensive spreading at shallow depths in the 

preserved parts of the pluton may be deceptive in indicating the original form. Only the terminal end of the 

upper part of the pluton is preserved, and it is possible 

that farther north the upper part, since removed by erosion, was much wider.

If batholiths do indeed narrow downward, the everpresent and often vexing problem of how crustal rocks 

accommodate to large intrusions assumes much smaller 

proportions. Strontium isotopic data (Hurley and others, 

1962, 1965; Fairbairn and others, 1964a, 1964b; Hedge 

and Walthall, 1963; Taylor and White, 1966; Ewart and 

Stipp, 1968) indicate that most granitic magmas are 

derived from upper mantle and lower crustal rocks and 

not from anatexis of silicic rocks higher in the crust. 

Trace- and rare-earth-element abundances indicate the 

same source (Taylor and White, 1966). Somewhat scanty 

data from the northern Cascades indicate a similar deepseated source for the plutons there. As masses of buoyant 

magmas rise through deep-seated and semiplastic rocks, 

these move aside and then back and downward into the 

space vacated by the rising magma. Such a process 

would continue until at higher levels the magma met 

cooler and more brittle rock. Magmatic spreading 

probably occurs in the transition zone between plastic 

and brittle rocks or, as Hamilton and Myers (1967) suggested near the surface beneath a covering crust of its 

own volcanic ejecta. Upwelling magma may lift or fracture or do both to brittle roof rocks.

The nature of the emplacement process is commonly 

reflected in the contacts of plutons; thus, as Buddington 

(1959, p. 715-731) has summarized, at catazonal depths 

there is general conformity between country rocks and 

intrusives, and chill zones bordering such intrusives are 

absent. Gradational and granitized contacts are 

prevalent. These features are characteristic of the oldest

plutons in the northern Cascades, such as those of 

Dumb ell Mountain, whereas plutons exposed only to 

epizonal depths, such as the Cloudy Pass, give ample 

evidence of emplacement in cool, brittle rocks. Here the 

room problem has been solved by lifting of the roof rocks, 

partly by upbowing and partly by upthrusting along 

marginal faults as at Hart Lake. The Duncan Hill pluton 

wedged apart country rocks at the lowest exposed levels 

and cuts abruptly across them at the uppermost levels. 

Inasmuch as there is no evidence that any of the rocks 

cut out by the pluton foundered in the magma, it can 

only be presumed they were lifted when cut off and, subsequently, were removed by erosion. Thus, the Duncan 

Hill pluton illustrates well the methods whereby an intrusion can make room for itself at depths ranging from 

mesozonal to hypabyssal.

AGES OF INTRUSIVE ROCKS 

AND RELATED PROBLEMS

Until the advent of radiometric dating, the ages of 

older intrusive rocks in the northern Cascades were 

generally designated vaguely as pre-Late Jurassic or 

pre-Late Cretaceous, and indeed there are few grounds 

on geologic evidence alone for more precise designations. 

Within the study area, relative ages of most intrusions 

can be determined, but here again, nearly all of the intrusions are contained only in metamorphic rocks, the 

ages of which were unknown until recently. Potassium/argon dating of most Tertiary plutons presented 

few problems, but because of reheating and the resetting 

of radiometric clocks, most of the older plutons were not 

accurately datable by this method. Even the oldest unit 

in the region, the Swakane Biotite Gneiss, and its 

equivalents, yielded Eocene ages (Engels and others, 

1976). In recent years, however, dating by other methods 

has provided a framework of reliable determinations sufficiently broad so that it is now possible on geologic 

grounds to date even most of the plutons for which 

radiometric dates are not yet available rather closely and 

with fair assurance.

Some of the most significant age dating in the 

northern Cascades was done by Mattinson (1972). He 

not only dated a number of the older plutons, but also established the Precambrian age of parent material in the 

Swakane Biotite Gneiss and the Precambrian age for a 

unit in Misch's (1966) Yellow Aster Complex. He also 

determined a late Paleozoic age for the "younger 

metamorphic rocks of the Holden area." Mattinson also 

proposed two periods of regional metamorphism, one of 

middle Paleozoic age occurring about 415 m.y. ago, and 

the other of middle to Late Cretaceous age, occurring 

from 60 to 90 m.y. ago. A minimum age of early 

Paleozoic or older is assigned to the Swakane. The ages 

of plutons in the mapped area for which area determinations have been made are summarized in table 39 from
94 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

e

0

Qc

 S

05

g

05~

1

-0

a

3

&

1O)

o

^

"0

e

a

e

"0

1

-c

 S

01

g

^> .^

Co

g

 S

 >.

O

05

|>

a

'£o

I

 2 '1

°f

05

co

% 

H

%

I

^

o

I $8

s

12

! !

^,

&

 %

S,

1

s

, _ , s

£

J

>

s

c

co _ _

X cB cB 1

a out

05" '§> ^ '&> ^ 't

2 "9 05 "0 05 1

1 ' O> i 1 O> i 1 < «r O " O - C

 8 CO' |oj | C/

£ -5 & rj £

o 5 o^^o *- 

U <i CB rj o> OB rj < _, ... J3 "O !, _C ~ _ , _£

^ OOO O JB >, O ° 13 22 >> "2 °°

o "§ 1 ft "3 1 ft ^ ,0 a^ 5 a^5 ^ c

cB C cB C cB 1 H D 0 D 0 £

'

c

- - i 'C1

.s .s .s : £

'> '> '> | £ ^

cB cB cB I -^ ^

^ . . ^ ; co &j

 !§ [S . ! ffi °l

^ O ^ o ' O> cB

i"s CtZr^ S " G |l C2 " * " «" tB | g-f C2 g ir tJD 05 i i «" K H^O3 §1H c* ,4

Q . *t3 Q . r*7] r s r*7] *^3 Q }TI r*7] T

» ^ !> | * ^ !> d * h,' d | !> *-Ju;d

ffi HlW H!-S ffi "-sin CU >-B

CM Oo^ O 10 ° ^^O ^ 00^

CM C^CMCM CM-* CM ^H^H^H CM i-H r-

-H ^ -H -H -H -H -H -H -H -H -H -H -f

i^ ?^ c^ LO CO CM CO C" O5 CO CM O5 C1*

CM m If* °°^3 CN COCO"* CO 3J^

|

|

'

>i

-2^ ^1

'2 J3

O dt

QJ N ST 01

-4J C O +J 'C o a C

0 fl QJ 0

^g ooo o ^ o.-^^s o oc

Q ' O ' O ' U ' O *3j _£j ' O co o ' O ' O T

g : : : -s a : -s § : :

(H ii i CB 3 i C *- i i

O . . , Q Cf > < O

3 ££< £< * <3£ * 3«

^ P^Jfci pfci ti fc£jfcijp ^ fcij^

! O) ! O>

T3 T3

« § C

QJ g^o) c'S'Ss <u 'oc * 3 a

 ti o -"S o »- o c -tS ' o -"^ c -

-U u -t^ U 0) '^ fc "^iCJ -t^ t2 + 2 S .2 S H ^ o 2 i *" -2 o . c

PQ N PQ N<: ffi PQ!N PQ ffiff

^ ^^ § § « ''

J 'I ^ ^ J2 c o

 *j >»3 o a a u, ~g

CB O) M M rj , i

-c -£ o> QJ QJ s a

co .2 cB O) O) o rt

n . OOO £*«]>> >SC O OC QQQ QCQ'O'O ^^c Q Q C

1 111 Is s

0 Q pi (S 0 Q

2

13

_u

i 'So 2 to -2

3 05 o

J r-H 01

5 n- 0

i -o co

3 cB § ^ CB

lldSdllc

11 i°|l H TO ^H

2 0 D

 i i

i i !

! ! I

i i i

! ! !

I I I

! ' !

' Ci '

i 1 :

. T3 . ^2 

i cB i O) 

i *-i i tU)

3 -§ O § H -c

; Q ; d

! "-S 1 l-j

^ p cq * i-; c~

H CO CM CM' CM i1 -H -H -H -H -f

J i I i I CM * C~

> * t> OJ o c~

" * LO LO t> Lf

i i i

i : i

i I '

i i i

i i i

! ' ! 01

01 . .*J i .t3 I C

' -2 ' T3 

3 « -S 0 M C

3 3 o "O -H "^

c 1 g ' «

cB »- , 3

O O , O"

(H JH t-i JH 1-

' & ^ fcij ^ ti

1 ! ' 01

O1 oj T3 .-a ; ts c a > 01 

> o 01 S 2 a

i S .2* I S .1

£ PQ S ffi PC

^

1 .s

c 5

'3 § 

J||

S o ^o S ^. ^

§ 3 ^ -2

T3 T2 a 3

o J5 3 'a 

ffi 0 *

j d c

3 Q C

3 0 C 

3 Tj3 -C

- LO C

H CM CS

1 -H 4 

- * c

3 CO CC

|

CQ

CO 'S

C

M

O)

 "g

_o

5 ^ c

3 .2 t:

cB i

3 , O" ,

i *" *- 3 <: <

- ^ t-^

4 HH H^

O)

T3

C

01

. 3 £

S *- 

5 ^ -2

ffi PQ

c

o

_3

1(3

s, 

1
GENERAL GEOLOGICAL PROBLEMS RELATING TO INTRUSIVE ROCKS 95

OOOOOOO OOOOOtn^oO

QQQQQQQ Q Q Q Q Q a «| Q

3 O O C

3 T3 T3 T

| ;

 q CM co p

H -H -H -\

H <* 1C ;

3 1C O C 

- C- Oi t1

-3

N

 B

CO

[

,

;

,

i

2 o o o c

3 T3 T3 T3 T

! ! '

3 C<l CO >-H r- H -H -H -H H

3 O 00 * r-

- O 00 <£> «

|

i

|

0)

_§

§

 5 CO

+J ~Q}

CO be

5 ^> SH C

! <5 ££] r,

S d

 -3 *-3

H rH CM O

H -H -H ^

i S 0 0

3 <x> a

CO

'a! 22

bo

-2 -2 _§ .§

D.H^^^^^^^^ ^

O> i i i i CO S '.',','.& i as S

a

.2

ts w

5 g 0 0 0 C

S ; ; ;

! o O

5 0 0 0 0 C

3 T3 T3 T3 T3 T

....

ir-s »^

5 O O O O C

3 T3 T3 T3 T3 T

! ! ' !

t i m / i ir

qT-H i ICM^H ^Hi-Hi-Hiv

H -H -H-H-H -H-H-H-t

-2's

3 '-3-'

0

CO

'S

£3

bO

-2 -2

1 1

§ r§ r§ r§1J r§ r«

i i i CO CO i

2 i

"53 i

CH '

bfi '

.-§ i c i o ,

5 O O ^ O O C

! ! co . i

! 0*0" ! H i i i i 0*0" i , i i O" . i

5 O C

3 T3 T

|

§CO

t/3 .£H

"3 4J

bo CO

5 ^ 5 C

3 W "=5 T:

0 S

3 1C 1C m. O C

5 i H T-H CO i-H TH -H -H -H -H 4 H ic oo co co cr

I T-H t- -X CO T

q oq oq og oq cv

5 C 

3 T

2 0 C 

3 T3 T

|

i

5 0 C 

3 T3 T

« tt

OH

,>§

.^

0,

&£§il, §§

,c_a,r!

0, £ fin

,r!,r!,r!,r!,G22,Q JDXJXJXJJD

0, 0, 0, CM 0, 0, 0, O, O, O, O, O, O, O,

0

MQ + 

3 C

53

2 C

3 C.

(

s

a 

i 2

U

5 C

3 C

)

1 a

3 .+ 

i C

3 |

ii

5 C

3 C

j

jj

5 C

3 C.

T

£

a I "2

U

5 C

3 C

j

2

a c

3 T 

1

!

-4

H +

c

^'i 

S

3 5^u0

ij

">

<

1

S

^ £

C

H a

M

iff

<!

j

1

0

^

£

a

ii

5 C

3 C

3

3

!

Mis

 > c 

3 C

c

rH 

H

3

 > c 

3 C

5 C 

3 T

5 C

3 C

5 C

5 C

3 C.

Mj: 

C

c/

5 C

3 C.

ii

2 0

5 C

3 C.

5 S

H 3 C/

5 C

3 C.

ii

2 0

5 C

3 C

c

3 T 

;

H

3

It

5 C

3 T

5 C

3 C

\ \

Q

^

a

It

Zircon -

.ans "c

3 

o

S--

 ^ <]) O

^§ 'S

jg 

O

o o o o JB

O

K

o o

Q Q

o o

Q Q

o o

Q Q
96 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

data presented by Engels and others (1976). Not included are those determinations that they, for various 

reasons, considered suspect or for geologic reasons are 

untenable. All the data presented by Mattinson (1972) 

concerning the Dumbell Mountain, Seven-fingered Jack, 

and Entiat plutons are included, however, to show the 

spread that different methods give.

The middle to Late Cretaceous period of metamorphism proposed by Mattinson, during which he believed 

the upper Paleozoic rocks and the Dumbell Mountain 

plutons together were metamorphosed to amphibolite 

grade, was also a period when a number of larger plutons 

or batholiths in the region were intruded. These include 

the about-90-m.y.-old Mount Stuart and Black Peak 

batholiths and the Tenpeak and White Mountain 

plutons (Engels and others, 1976). There can be no question that potassium/argon radiometric clocks were reset 

in many rocks 60 to 90 m.y. ago, but as is discussed later, 

there is little or nothing to suggest rather intense 

regional metamorphism at that time other than what 

has been interpreted as the metamorphic nature of the 

Dumbell Mountain and Seven-fingered Jack plutons 

and their correlatives (Mattinson, 1972, p. 3772; Misch, 

1966; Crowder, Tabor, and Ford, 1966; Crowder, 1959). 

The upper Paleozoic rocks of the Holden area believed 

by Mattinson to have been metamorphosed to gneisses 

60 to 90 m.y. ago were already gneisses when intruded by 

the Dumbell Mountain plutons 220 m.y. ago as proved 

by disoriented inclusions of gneiss and schist within the 

plutons. To regionally metamorphose the Dumbell 

Mountain (and Seven-fingered Jack) plutons to 

amphibolite grade and leave untouched the discordant 

metamorphic fabric of these inclusions seems unlikely. 

Rocks as susceptible to recrystallization as the contact 

complexes, characterized by abundant gabbro and very 

coarse grained hornblendite, that border the Entiat 

pluton (fig. 25) and other supposed premetamorphic 

plutons are equally unlikely to have completely escaped 

any metamorphic changes. All these complexes also contain abundant inclusions of disoriented fragments of 

metamorphic country rocks. More likely, the host rocks 

were metamorphosed before or near the time Dumbell 

Mountain quartz diorite was intruded. Potassium/argon 

radiometric clocks were as widely reset in late Eocene 

time as during mid- and Late Cretaceous time, as is indicated by late Eocene potassium/argon ages obtained 

from rocks such as the Leroy Creek pluton and the 

Swakane Biotite Gneiss and its equivalents (Engels and 

others, 1976), but no one has credited this heating event 

with producing such dire effects on the terrane as had 

the proposed earlier event.

Mattinson considered the Chelan Complex of Hopson 

(Mattinson, 1972, p. 3772) to be a metamorphosed, 

migmatized, and mobilized extension of Misch's (1966) 

Marblemount belt, which includes the Dumbell Mountain plutons (Mattinson, 1972, fig. 1, p. 3770). Moreover, 

the Dumbell Mountain plutons, and hence the 

Marblemount belt, pinches out in the southern part of 

the Lucerne quadrangle, and the correlation of the 

Chelan Complex with the Marblemount belt is invalid.

The Chelan Complex of Hopson probably correlates 

with the Seven-fingered Jack plutons, although a strip of 

Entiat pluton rocks, just southwest of the location of 

Mattinson's sample 23 (1972, fig. 1, p. 3770), is 

designated as "Late Cretaceous and Tertiary." This 

designation is based on potassium/argon ages of about 61 

and 64 m.y. obtained from biotite and hornblende 

(Engels and others, 1976), roughly the same as the potassium/argon ages (60 to 82 m.y.) obtained from rocks 

nearby in the Chelan Complex from which Mattinson 

(1972) obtained zircon Pb20B/U238 ages ranging from 100 to 

183 m.y., and sphene ages of 71 to 87 m.y. No zircon 

Pb20B/U2:i8 age determinations from the strip of Sevenfingered Jack rocks labeled as "Late Cretaceous and 

Tertiary" have been made, and until this is done, there 

is no more reason for calling these rocks Late Cretaceous 

and Tertiary than for calling the Chelan Complex Late 

Cretaceous and Tertiary on the basis of potassium/argon 

ages and ignoring the zircon lead/uranium ages. The 

Seven-fingered Jack rocks, including the Chelan 

Complex, are far more nearly akin, petrologically, to the 

older intrusives than to any of the Tertiary intrusive 

rocks, including the about-60-m.y.-old (Engels and 

others, 1976) Clark Mountain stocks.

The lower beds in Paleocene Swauk Formation in the 

Chiwakum graben, in the Holden quadrangle, contain 

numerous pebbles and boulders identical to nearby outcrops of both the Dumbell Mountain and the Sevenfingered Jack intrusive rocks, indicating thereby that 

these rocks were exposed during that time. On the other 

hand, the formation contains pebbles and cobbles of extrusive rocks, but the affinities of these rocks are unknown, unless, perhaps, they are extrusive equivalents of 

the Clark Mountain stocks or somewhat older plutons. 

But it does seem unlikely that the Dumbell Mountain 

plutons, in particular, could have been eroded to 

catazonal depths during or so soon after the time they 

were supposed to have been metamorphosed about 90 

m.y. ago.

COMPOSITION AND DIFFERENTIATION

Compositions of the various intrusive rocks in the 

study area were determined by 47 chemical analyses and 

more than 300 modal analyses. Of the chemical analyses, 

7 were by standard methods and 40 by various rapid 

methods; all chemically analyzed samples were also 

analyzed by spectrographic means for semiquantitative 

determination of minor elements. Modes were determined on thin sections of standard size with a point
GENERAL GEOLOGICAL PROBLEMS RELATING TO INTRUSIVE ROCKS 97

counter of the type described by Chayes (1949). Analyses 

of rocks from the Cloudy Pass batholith have been 

reported earlier (Cater, 1969; Tabor and Crowder, 1969) 

and are not repeated here. Inasmuch as none of the rocks 

are particularly coarse grained, stained slabs were not 

used for modal determinations.

For most of the smaller intrusions of relatively uniform 

compositions only single, representative, mostly composite samples were chemically analyzed, but for larger 

plutons that are zoned or are otherwise of variable composition, a number of samples were commonly analyzed. 

The chemical analyses supplemented by numerous 

modal analyses are thought to give a fairly representative view of the compositions of each intrusive. Even 

for the salic, quartz-bearing plutons, apart from the gabbroic contact complexes associated with some of them, 

the range is fairly wide; Si02 , for example, ranges from 

about 56 to about 76 percent. The range for some of the 

larger, compositionally variable plutons, moreover, is 

nearly as large as the range for the entire group of 

plutons. A number of plutons are closely similar in composition, some because they are closely related in time 

and probably in source; but other compositionally 

similar plutons are probably unrelated, being separated 

in time by scores of millions of years. All, however, 

probably originated under somewhat similar conditions 

and from similar materials presumably from the upper 

mantle and lower crust. The older, narrow, quartzbearing plutons mostly show much less diversity in composition than do the latest Cretaceous and younger 

plutons. In fact, only the largest plutons, mostly Tertiary, are compositionally zoned or have considerable 

variability at exposed levels. However, as explained 

earlier, presumably only the roots or feeders of the older 

intrusions remain, and these narrow conduits would 

seem to be physically unfavorable locations for 

demonstrable zoning resulting from differentiation to occur, particularly in more or less horizontal planes, 

although these narrow masses certainly seem to represent levels in vertical zones.

Probably the most characteristic feature distinguishing the intrusive rocks of the area is their low content of K 2 0, relative to average intrusive rocks 

(Nockolds, 1954) of similar Si02 content. This low K20 

content is true regardless of age of an intrusive, although 

in general, the older the rock the lower the content of 

K2 0 even where Si02 is high. Indeed, the older preTertiary plutons, even the most quartzose, are virtually 

devoid of potassium feldspar, and biotite is not common. 

Of the pre-Tertiary plutons, only the Bearcat Ridge, 

Sulphur Mountain, and High Pass plutons contain more 

than rare, interstitial amounts of potassium feldspar. 

The Sulphur Mountain pluton has a radiometric age of 

70 m.y. (Engels and others, 1976), indicating a Late 

Cretaceous age; the undated High Pass pluton cuts the

Sulphur Mountain, and possibly the High Pass may be 

as young as Tertiary. The undated Bearcat Ridge 

plutons both structurally and in megascopic appearance 

closely resemble the Dumbell Mountain plutons and 

were shown on the Lucerne geologic quadrangle map as 

being contemporaneous. The Bearcat Ridge rocks, 

however, are not in contact with any of the older dated 

rocks, so their age relative to older intrusive rocks is not 

known. Norms and modal data indicate that, compositionally, the Bearcat Ridge rocks are more nearly 

akin to far younger rocks, and it may be that these rocks 

are younger than was indicated on the map.

Hietanen (1975) has proposed an explanation for the 

origin of the potassium-poor magmas in the northern 

Sierra Nevada that may explain the potassium-poor intrusive rocks in the northern Cascades. Her explanation 

was based on the experimental work by Alien, Modreski, 

Haygood, and Boettcher (1972) and Modreski and Boettcher (1972) on stabilities of amphiboles and biotite or 

phlogopite at high temperatures and pressures. Their experimental work indicated that amphiboles become unstable at depths of about 75 km, whereas phlogopite only 

begins to decompose at depths greater than 100 km and 

is unstable below 175 km. Hence, in a subducting 

lithospheric plate, amphibole would break down to 

release water and sodium to magmas forming at depths 

shallower than 100 km, whereas potassium would be 

retained in phlogopite or biotite and would only be 

released to magmas formed at depths greater than 100 

km. Thus, possibly the magma for the potassium-poor 

intrusions in the study area were formed at relatively 

shallow depths.

The Dumbell Mountain plutons, the oldest of the major intrusives in the area (there may possibly be some 

older metamorphosed dikes and sills in the Swakane 

Biotite Gneiss), have compositions that appear to be 

unique. In fact, a search of the literature, albeit not an 

exhaustive one, failed to disclose any analyses of igneous 

rocks having comparable contents of silica, iron, 

magnesium, and calcium where K2 0 was so astonishingly low; the rocks are extremely potassium-deficient 

quartz diorites (table 3). The perhaps not much younger 

but undated Leroy Creek pluton is about equally 

deficient in K20, but its trondhjemitic composition is 

not particularly unusual. Both younger pre-Tertiary and 

Tertiary plutons also are without exception poorer in 

K2 0 than is normal for rocks of otherwise comparable 

compositions. In fact, only in the porphyries and 

granophyres at the top of the Eocene Duncan Hill pluton 

does the content of K20 reach levels normal for rocks of 

similar silica contents.

Rocks from the Dumbell Mountain plutons have a 

considerable compositional range, the analyzed samples 

containing from 52.5 to 73.7 percent Si02 . All other major constituents decrease as silica increases except Na 2 0,
98 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

which remains fairly constant, and K2 0, which also remains constant but very low (table 3; figs. 12, 13). 

Hornblende-quartz diorite gneiss is compositionally the 

most variable of the Dumbell Mountain rocks, possibly 

because of considerable but locally variable quantities of 

partly assimilated hornblendic host rocks. The quartz 

diorite augen gneiss is considerably more siliceous than 

the slightly younger gneissic hornblende-quartz diorite 

and contains a little less K2 0. The variations of compositions within the plutons, as indicated by modal analyses 

of numerous samples (table 2; fig. 11), are erratic and indicate no systematic zoning. Systematic zoning, as indicated by modal analyses, also appears to be lacking in 

the rest of the pre-Tertiary intrusives within the area, 

although local variations of composition are appreciable 

and common. In the Glacier Peak quadrangle, however, 

Crowder, Tabor, and Ford (1966) mapped a dark, mafic 

facies in the northern part of the Ten peak pluton; the 

other mapped units in the pluton differ from each other 

not so much in composition as in structure and texture. 

Tertiary intrusive rocks are compositionally more 

varied on the whole, and the distribution of compositional variations is generally more systematic than is 

true of the older intrusive rocks. The smaller plutons are 

relatively homogeneous, and variations in content of 

K2 0 are rather small. The two largest plutons, the 

Cloudy Pass and Duncan Hill, on the other hand, contain rocks of widely different compositions. In the 

Duncan Hill pluton the compositional variations, in 

general, are systematic and show progressive changes 

along the length of the pluton, whereas in the Cloudy 

Pass variations are largely erratic and range between 

wide limits across short distances. The composition, the 

variations therein, and the reasons for these variations in 

the Cloudy Pass batholith were discussed at length by 

Cater (1969) and Tabor and Crowder (1969). The parts of 

the batholith described by each of these reports differ 

somewhat in the abundance of rock facies exposed and in 

the relative significance of differentiation processes 

operative in the batholith to produce these facies. The 

core of the batholith in the Holden quadrangle, 

described by Cater (1969), is characterized by rocks containing labradorite, the composition of which changes 

little from place to place. The abundance of orthoclase 

can range from none to abundant within distances 

measured only in a few meters. Rocks containing sodic 

plagioclase are rare and mostly confined to late dikes. To 

the west in the part of the batholith described by Tabor 

and Crowder (1969), much of the rock is a light-colored, 

oligoclase-bearing quartz monzonite, containing fairly 

constant amounts of potassium feldspar. Inasmuch as 

the batholith is only now in the process of being deroofed 

and is exposed only to depths not exceeding 1.6 km, it afforded a particularly advantageous opportunity to study 

subvolcanic phenomena associated with the upper part

of a batholith. The Duncan Hill pluton, on the other 

hand, affords an opportunity to view a large intrusion 

not only from a similarly shallow level but also to depths 

of a fair number of kilometers.

Other plutons, because of their narrow vertical ranges 

of exposure or ranges, at any event, that show little or no 

consistent compositional variation, seem to correspond 

more or less to given narrow levels within the broad 

spectrum of depth zones observable along the length of 

the Duncan Hill pluton. Older intrusives, such as the 

Dumbell Mountains plutons, may indicate the kinds of 

rocks existing at deeper levels in the Duncan Hill. Not 

all plutons that are older than the Duncan Hill, however, 

seem to have been eroded as deeply as the north end of 

the Duncan Hill. The older Clark Mountain stocks to the 

west, on the opposite side of the Chiwawa graben, for example, have the general characteristics of rocks near the 

midpoint along the length of the Duncan Hill. In fact, in 

the Holden quadrangle, the terrane on the west side of 

the graben, in general, seems not to have been as deeply 

eroded in Tertiary times as that on the east side. The 

only lower Paleozoic or older Swakane Biotite Gneiss exposed west of the graben is in the roof of the Cloudy Pass 

batholith, and plutons older than or equal in age to those 

east of the graben have the characteristics of shallower 

intrusions.

Because the compositional and textural difference 

present in plutons of progressively younger ages roughly 

parallel the changes that occur at increasingly shallow 

depths in the Duncan Hill pluton, probably the differentiation processes that were active in the Duncan Hill 

were equally active in the other granitoid intrusives of 

the area. In the Duncan Hill, however, the processes can 

be interpreted with reasonable assurance without 

recourse to a series of extrapolative leaps that would be 

necessary were the evidence only a series of fragments 

preserved in a series of separate intrusives. Hence, the 

Duncan Hill was investigated in more detail outside the 

mapped quadrangles because of information it probably 

gives on the history of differentiation of other plutons in 

the area.

The plot of modes of rocks from the Duncan Hill 

pluton in figure 77 shows a wide scatter consistent with 

the wide compositional range of the rocks in the pluton; 

the plotted norms (fig. 79), on the other hand, although 

showing a considerable scatter, are confined to a narrow 

field extending from near the center of the triangle 

towards the albite corner. As shown by the variation 

diagram (fig. 78), in which major oxides are plotted 

against Si02 , only K20 increases as Si02 increases, 

although somewhat erratically, but as is well known, 

K2 0 is commonly the most variable oxide in granitic 

rocks. Na2O remains nearly constant; for that matter, it 

ranges between narrow limits in all the granitoid plutons 

of the area. Bateman and Dodge (1970, p. 414) also found
GENERAL GEOLOGICAL PROBLEMS RELATING TO INTRUSIVE ROCKS 99

that the Na20 content is about the same in the plutons 

in the central part of the Sierra Nevada batholith. 

As they pointed out, the content of SiOs in granitic 

rocks is a measure of differentiation, but it appears that 

the content of Na20 does not vary systematically with 

differentiation.

Of particular interest is figure 98, a diagram showing 

the variations in Si02, K20, Na2 0, and CaO along the 

length of the pluton. SiC>2 and K20 are the only constituents that increase higher in the pluton, and Na20 

remains virtually constant throughout. As indicated in 

figure 98, the only abrupt changes in composition of the 

Duncan Hill occur in the miarolitic and granophyric 

rocks at the south end of the pluton where the content of 

K2 0 about doubles and CaO decreases to a third of its 

value lower in the pluton. As shown in table 23, ferric oxide also increases slightly at the expense of ferrous oxide 

in the miarolitic rock, possibly the result of contamination with atmospheric oxygen at these shallow levels. 

Although a gap of about 15 km separates analyzedsample 7 from the analyzed samples at the south end of 

the pluton around Stormy Mountain, the reality of the 

abrupt change is confirmed by study of thin sections of 

samples in the intervening interval. The change in composition is as abrupt and occurs in the same interval as

NORTH END

76 idoes the change in megascopic appearance in the rather 

narrow transition zone between biotite granodiorite and 

miarolitic quartz monzonite. Furthermore, unlike the 

underlying biotite granodiorite, the highly gas-charged 

miarolitic quartz monzonite appears to have been totally 

molten immediately prior to final crystallization. The 

oscillatory and patchy zoned plagioclase having 

labrodorite cores in the rock below the quartz monzonite 

is replaced by oligoclase showing progressive but little or 

no oscillatory zoning; cores of labradorite are either nonexistent or where rarely present are highly saussuritized 

and nearly resorbed. That the Duncan Hill magma was 

moderately wet is suggested by the occurrence of 

hornblende and biotite to the total exclusion of pyroxene. Yoder (1969, p. 83-84) has pointed out that only at 

elevated water pressures can plagioclase of high 

anorthite content form at temperatures of less than 

1250°C. The labradorite and a few bytownite cores in 

plagioclase having average compositions of generally 

sodic to medium andesine indicates high water pressures 

at the beginning of crystallization. Hence, a sufficient 

source of water at depth in the pluton for eventual 

transfer upward seems probable.

Abundant evidence indicates the Cloudy Pass 

batholith also contained considerable water (Cater,

SOUTH END

 116

Hornblende-biotite-quartz diorite

Miarolytic quartz monzonite

60

20 30 

PLUTON LENGTHEN KILOMETERS

40

FIGURE 98. Diagram showing variation in content of SiO2 , K2O, Na2O, and CaO along the length of the Duncan Hill pluton, central 

Washington. Sample analyses are given in table 23; sample locations (fig. 76) are projected to the center line of the pluton. Hornblendebiotite-quartz diorite probably crystallized at least 8-10 km below the miarolytic quartz monzonite. Biotite granodiorite probably crystallized 

at least 3-6 km below the miarolitic quartz monzonite.
100 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

1969), but the compositional changes in the rocks in the 

Cloudy Pass resulting from degassing of the cooling 

batholith are markedly different from those that occurred in the Duncan Hill pluton. There are no indications, 

for example, that rocks in the upper part of the Cloudy 

Pass were remelted prior to final crystallization; only 

large-scale but erratic metasomatism occurred along 

with features indicative of violent expulsion of gas and 

extrusive activity. The remaining uppermost part of the 

Duncan Hill pluton shows no features suggestive either 

of explosive escape of gas or extrusion of lava. One seems 

forced to the conclusion that the roof of the Cloudy Pass 

was leaky, whereas that of the Duncan Hill was tight and 

permitted only slow escape of volatiles as the pluton 

crystallized. Had volatiles from the Duncan Hill been 

able to escape readily, there seems little likelihood that 

water-vapor pressures could have risen to the point 

where labradorite cores of the plagioclase crystals, with 

which the magma must have been charged, could have 

gone back into solution in a magma now almost completely liquid. The miarolitic and granophyric quartz 

monzonite then finally crystallized from this almost 

completely liquid magma to a rock bearing little outcrop 

resemblance to the underlying granodiorite into which it 

grades.

The depth at which the miarolitic quartz monzonite 

crystallized is not known, but if the water vapor was approximately equal to the lithostatic pressure when the 

quartz monzonite crystallized, as indicated by the position of samples of quartz monzonite on the isobaric lines 

(Tuttle and Bowen, 1958, p. 74-75) in figure 79 (a pressure of about 150,000 kilopascals), then the^quartz monzonite solidified at a depth of 8 or 9 km a depth, 

however, that seems excessive for such volcanicappearing rocks. Perhaps the water-vapor pressure considerably exceeded the lithostatic load. Certainly considerable water pressure was necessary to accomplish 

resolution of the plagioclase. The probable depths of 

samples of granodiorite and quartz diorite below the 

miarolitic quartz monzonite are interpreted from the 

dips of remnants of Miocene lava caps remaining on 

ridges south of the Lucerne quadrangle and are believed 

to be minimal.

The progressive enrichment upward of SiO2 and K2O 

in the Duncan Hill pluton probably resulted from 

transfer of these components in supercritical aqueous 

solutions, rather than from differentiation by crystal 

fractionation. However, the decrease in CaO and mafic 

constituents higher in the pluton seems to be more than 

would be likely if the only changes were the addition of 

SiO2 and K2O strictly by metasomatism, so possible 

sinking of heavier minerals in the magma may have had 

a minor effect on composition. Furthermore, the 

protoclastic texture of the quartz diorite in the northern and lower part of the pluton suggests that filter

pressing upward of the still fluid, more silicic fraction of 

the magma may also have been effective. In any event, 

the protoclastic textures do indicate crowding and 

mutual interference of crystals while the magma was 

still in motion.

Metasomatic transfer of SiO2 and K2 O was equally effective in causing compositional variation in the Cloudy 

Pass batholith (Cater, 1969), but the variations there 

were much more haphazard than in the Duncan Hill. 

The efficacy of potassium metasomatism in altering 

compositions of intrusions has been documented by 

many geologists as, for example, Boone (1962), Kennedy 

(1953), and Taubeneck (1967) and is supported by a 

large body of experimental work (Burnham, 1967; Jahns 

and Burnham, 1958; Kennedy, in citing Mosey, 1955, p. 

498; Luth and others, 1964; Orville, 1963; Tuttle and 

Bowen, 1958, p. 90-91). Possibly this same process has 

operated effectively in other plutons in the area and may 

explain the extreme poverty of K2O in the Dumbell 

Mountain plutons. Potassium added to one rock or 

magma must have been taken from another somewhere 

else, and commonly only rocks enriched in potassium 

have elicited much attention because evidence of enrichment is far more obvious than evidence of depletion. The 

remaining parts of the Dumbell Mountain, Leroy Creek, 

and Seven-fingered Jack plutons may have been sites of 

potassium depletion.

The numerous Tertiary dikes in the area of widely differing compositions suggests that differentiation 

probably by crystal fractionation was also effective. 

Many of the dikes are aschistic and some are directly 

traceable into or are identical in composition and appearance to some of the larger plutons, but others are 

diaschistic and unlike the rocks of any of the larger 

plutons as, for example, the swarm of mafic dikes and irregular masses associated with the south end of the 

Duncan Hill pluton. The localities or magma chambers 

where the differentiation occurred, however, either have 

not been recognized or are not exposed. The large 

number of late Eocene intrusives in and adjacent to 

the mapped area that differ but little in age certainly 

suggests a widespread and copious source for large quantities of magma. Inasmuch as available data from strontium isotopes (Hedge and others, 1970; Church and 

Tilton, 1973; Peterman and others, 1970; Zell, 

Peterman, written commun., 1975) indicates the source 

of most magmatic material is the lower crust and upper 

mantle, then plenty of room exists in the remainder of 

the crust below the presently exposed surface for magma 

chambers to have formed. Such chambers not only could 

have fed the exposed plutons but also were sites where 

differentiates could have accumulated that were later 

forced into the dikes and small, irregular masses of 

widely different compositions that cut the area.
GENERAL GEOLOGICAL PROBLEMS RELATING TO INTRUSIVE ROCKS 101

TEXTURES AND DEPTH ZONES

The fact that textures of igneous rocks vary with rate 

of cooling and with depth of emplacement is well known, 

but much that has been written concerning textures applied only to mesozonal or shallower intrusions rocks 

with so-called typical igneous textures. Deep-seated igneous rocks, on the other hand, often have been interpreted as recrystallized or as having been formed by 

replacement, because the textures were considered 

metamorphic. Thus, Crowder (1959), from his study of 

thin sections of the Dumbell Mountain, Leroy Creek, 

and Seven-fingered Jack plutons, considered these rocks 

to be either largely recrystallized or to have formed by 

replacement or granitization. Van Diver (1967) considered the rather deeply eroded 90-m.y.-old White 

Mountain pluton to be recrystallized; he interpreted the 

protoclastic texture to be a recrystallized cataclastic texture, although the foliation of the protoclastic rock is 

conformable to the nearest contact of the pluton and 

over large areas transects the regional foliation of the 

metamorphic host rocks. Identical textures also exist in 

most of the Tertiary plutons, including the Miocene 

Cloudy Pass batholith, as previously discussed in the 

section on "Ages of intrusive rocks and related 

problems." Mattinson (1972) also considered the 

Dumbell Mountain plutons and their correlatives and 

Hopson's Chelan Complex probably correlative of the 

Seven-fingered Jack plutons to be metamorphosed, the 

Chelan Complex to the point of anatexis.

Misch (1966, p. 106 and fig. 7-1) considered the 

northward correlative of the Dumbell Mountain 

plutons his Marblemount Meta Quartz Diorite a part 

of his "basement complex" that had undergone his 

"Skagit metamorphism," an event, incidentally, by 

which he derived his "Skagit Gneiss" our Swakane 

Biotite Gneiss from the "Cascade River Schist" (p. 

113). Mattinson (1972) has dated the Cascade River 

Schist as late Paleozoic and the Skagit Gneiss as 

Precambrian. Misch also showed the Dumbell Mountain 

plutons (his fig. 7-1) as overthrust by the upper 

Paleozoic gneisses, rather than intrusive into them but 

did concede (his p. 114), "the meta quartz cliorite has 

relict gross igneous textures." These examples illustrate 

some of the interpretations of deep-seated intrusive 

rocks in the area that have been published by various 

geologists, but there are, however, a number of reasons 

for believing these rocks have not been metamorphosed, 

or only weakly so, since they were intruded. These 

reasons are discussed below.

As Crowder (1959, p. 843) noted, the hornblendequartz diorite augen gneiss of the Dumbell Mountain 

plutons contains unoriented inclusions of schist and 

gneiss. He considered these inclusions to be mobilized 

breccias resulting from granitization. In addition to containing these unoriented inclusions, much of the rock in 

both the Dumbell Mountain and Leroy Creek plutons 

has swirled foliation that is independent of regional 

foliation in the metamorphic host rocks; furthermore, 

foliation in the Leroy Creek pluton tends to parallel its 

contacts. Had regional metamorphism occurred after 

emplacement of the plutons, then the disoriented 

foliated fabric of the inclusions could not have survived 

regional recrystallization of supposed amphibolite grade. 

Were the inclusions confined to the central parts of 

plutons, it could be argued, perhaps, that the competent 

plutonic rocks shielded the inclusions from strong 

metamorphic effects; however, disoriented inclusions are 

most common near contacts, as other inclusions are. 

Also, it is difficult to account for the swirled foliation 

resulting from regional metamorphism where no swirled 

foliation exists in the enclosing gneiss and schist. 

Although the textures of the plutons resemble crystalloblastic textures, most thin sections contain plagioclase 

that shows both vague oscillatory and patchy zoning. 

Furthermore, younger plutons such as the Sevenfingered Jack have textures that verge on crystalloblastic 

in appearance in most places but not to the extent that is 

characteristic of the older and deeper seated plutons; 

textures of some of the Seven-fingered Jack rocks are 

typically hypidiomorphic. It is equally difficult to explain how the spectacular coarse-grained contact complexes associated with the Seven-fingered Jack and other 

presumed premetamorphic plutons and containing innumerable foliated metamorphic rock in all orientations, 

completely escaped recrystallization while their consanguineous plutons were being reduced to amphibolitegrade gneisses.

Rocks crystallized from magma intruded into material 

where conditions of amphibolite grades of metamorphism exist would probably differ texturally from rocks 

prystallized from magma injected into material where 

conditions of greenschist metamorphic facies or cooler 

conditions prevail. If, as Buddington (1959, p. 676) estimated, rock temperatures at the top of the catazone are 

about 500°C, then plagioclase in a crystallizing magma, 

for example, would have ample opportunity to 

equilibrate, and oscillatory and patchy zoning, so 

characteristic of plagioclase in mesozonal and epizonal 

rocks, would be largely destroyed, as is true in rocks from 

the Dumbell Mountain and Leroy Creek plutons and in 

most of the rocks in the Seven-fingered Jack and Entiat 

plutons. Extremely slow rates of cooling of magma intruded into regionally hot rocks should not be expected 

to yield rock having textures usually referred to as 

typically igneous. Most likely, textures more nearly 

resembling crystalloblastic textures should result. The 

generally pseudocrystalloblastic textures of the Dumbell 

Mountain and Leroy Creek plutons and much of the rock 

in other older pre-Tertiary plutons, and the gneissic
102 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

fabric of these rocks, can hardly have been formed by 

metamorphic recrystallization, leaving unaffected the 

attitudes of gneissic foliation in disoriented inclusions 

and slabs. The gneissic fabric of the quartz diorite is 

probably the result of overgrowths on crystals oriented 

by flowage at early stages of crystallization.

It is true, nevertheless, that rocks in the area have 

been sufficiently reheated periodically to yield anomalously low potassium/argon ages for both metamorphic 

and pre-Tertiary intrusive rocks (Engels and others, 

1976). Moreover, in many places leucocratic and trondjhemitic clots, dikes, and small irregular bodies have 

either segregated from or been injected into the 

metamorphic rocks and the Seven-fingered Jack and 

older plutons; but the abundance of these leucocratic 

rocks everywhere in the Swakane and their localized distribution in the younger metamorphic rocks and the 

plutons strongly suggests that they are not of the same 

age. Some of the masses in the Swakane may well be 

Precambrian. In any case, there is little to suggest strong 

regional metamorphisms subsequent to intrusion of the 

Dumbell Mountain plutons.

REFERENCES

Alien, J. C., Modreski, P. J., Haygood, Christine, and Boettcher, A. L., 

1972, The role of water in the mantle of the Earth; the stability of 

amphiboles and micas: International Geological Congress, 24th, 

Montreal, 1972, Proceedings, Sec. 2, p. 231-240.

Bailey, E. B., and Maufe, H. B., 1960, The geology of Ben Nevis and 

Glen Coe and the surrounding country (explanation of sheet 53): 

Geological Survey of Scotland, Memoir, 307 p.

Bateman, P. C., 1965, Geology and tungsten mineralization of the 

Bishop district, California, with a section on Gravity study of 

Owens Valley, by L. C. Pakiser and M. F. Kane, and a section on 

Seismic profile, by L. C. Pakiser: U.S. Geological Survey Professional Paper 470, 208 p.

Bateman, P. C., and Dodge, F.C.W., 1970, Variations of major 

chemical constituents across the central Sierra Nevada batholith: 

Geological Society of America Bulletin, v. 81, no. 2, p. 409-420.

Blake, D. H., and others, 1965, Some relationships resulting from the 

intimate association of acid and basic magmas [with discussion]: 

Geological Society of London Quarterly Journal, v. 121, pt. 1, no. 

481, p. 31-49.

Boone, G. M., 1962, Potassic feldspar enrichment in magma Origin of 

syenite in Deboullie district, northern Maine: Geological Society 

of America Bulletin, v. 73, no. 12, p. 1451-1476.

Bowes, D. R., Kinlock, E. D., and Wright, A. E., 1964, Rhythmic 

amphibole overgrowths in appinites associated with explosionbreccias in Argyll: Mineralogical Magazine, v. 33, no. 266, p. 

963-973.

Brown, G. M., 1956, The layered ultrabasic rocks of Rhum, inner 

Hebrides: Royal Society of London Philosophical Transactions, 

series B., v. 240, no. 668, p. 1-53.

Buddington, A. F., 1959, Granite emplacement with special reference 

to North America: Geological Society of America Bulletin, v. 70, 

no. 6, p. 671-748.

Burnham, C. W., 1967, Hydrothermal fluids at the magmatic stage, 

[chap. 2] in Barnes, H. L., ed., Geochemistry of hydrothermal ore 

deposits: New York, Holt, Rinehart and Winston, Inc., p. 34-76.

Cater, F. W., 1960, Chilled contacts and volcanic phenomena associated with the Cloudy Pass batholith, Washington, in Short 

papers in the geological sciences: U.S. Geological Survey Professional Paper 400-B, p. B471-B473.

____1969, The Cloudy Pass epizonal batholith and associated subvolcanic rocks: Geological Society of America Special Paper 116, 

53 p. 

_1970, Geology of the salt anticline region in southwestern

Colorado with a section on. Stratigraphy, by F. W. Cater and L. C.

Craig: U.S. Geological Survey Professional Paper 637, 80 p. [1971]. 

Cater, F. W., and Crowder, D. F., 1967, Geologic map of the Holden

quadrangle, Snohomish and Chelan Counties, Washington: U.S.

Geological Survey Geologic Quadrangle Map GQ-646, scale

1:62,500. 

Cater, F. W., and Wright, T. L., 1967, Geologic map of the Lucerne

quadrangle, Chelan County, Washington: U.S. Geological Survey

Geologic Quadrangle Map GQ-647, scale 1:62,500. 

Chamberlin, R. T., and Link, T. A., 1927, The theory of laterally

spreading batholiths: Journal of Geology, v. 35, no. 4, p. 319-352. 

Chayes, F. A., 1949, A simple point counter for thin-section analysis:

American Mineralogist, v. 34, nos. 1-2, p. 1-11. 

Church, S. E., and Tilton, G. R., 1973, Lead and strontium isotopic

studies in the Cascade Mountain bearing on andesite genesis:

Geological Society of America Bulletin, v. 84, no. 2, p. 431-454. 

Cloos, Hans, 1923, Das Batholithenproblem: Fortschritte der Geologie

und Palaeontologie, v. 1, no. 1, p. 1-80. 

Crowder, D. F., 1959, Granitization, migmatization, and fusion in the

northern Entiat Mountains, Washington: Geological Society of

America Bulletin, v. 70, no. 7, p. 827-878. 

Crowder, D. F., Tabor, R. W., and Ford, A. B., 1966, Geologic map of

the Glacier Peak quadrangle, Snohomish and Chelan Counties,

Washington: U.S. Geological Survey Geologic Quadrangle Map

GQ-473, scale 1:62,500. 

Daly, R. A., 1912, Geology of the North American Cordillera at the

forty-ninth parallel: Canada Geological Survey Memoir 38, 857 p.

Davis, G. A., 1977, Tectonic evolution of the Pacific 

Northwest Precambrian to present: Washington Public Power 

Supply System, Subappendix 2 RC, Preliminary Safety Analysis 

Report, Amendment 23, Nuclear Project No. 1, p. 2, 

RC-1-2RC-46.

Davis, G. A., Monger, J.W.H., and Burchfiel, B. C., 1978, Mesozoic 

construction of the Cordilleran "collage," central British Columbia to central California, in Howell, D. C., and Dougall, K. A., 

eds., Mesozoic paleogeography of the western United States: Los 

Angeles Society of Economic Paleontologists and Mineralogists, 

Pacific section, p. 1-31.

Dickinson, W. R., 1976, Sedimentary basins developed during evolution of Mesozoic-Cenozoic arc-trench system in western North 

America: Canadian Journal of Earth Science, v. 13, no. 9, p. 

1268-1287.

Dietrich, R. V., 1961, Petrology of the Mount Airy "granite": Virginia 

Polytechnic Institute Bulletin, Engineering Experiment Station 

Series 144, no. 6, p. 5-63.

DuBois, R. L., 1954, Petrology and ore deposits of the Holden mine 

area, Chelan County, Washington: Seattle, University of 

Washington, Ph. D. thesis.

____1956, Petrology of the Holden mine area, Wash, (abs.): 

Geological Society of America Bulletin, v. 67, no. 12, pt. 2, p. 1766.

Engels, J. C., Tabor, R. W., Miller, F. K., and Obradovich, J. D., 1976, 

Summary of K-Ar, Rb-Sr, U-Pb, Pb207/Pb206 , and fission-track 

ages of rocks from Washington State prior to 1975 (exclusive of 

Columbia Plateau basalts): U.S. Geological Survey Miscellaneous Field Studies Map MF-710, scale 1:1,000,000, 2 sheets.
REFERENCES 103

Erickson, E. H., Jr., 1969, Petrology of the composite Snoqualmie 

batholith, central Cascade Mountains, Washington: Geological 

Society of America Bulletin, v. 80, no. 11, p. 2213-2236.

Ewart, A., and Stipp, J. J., 1968, Petrogenesis of the volcanic rocks of 

the central North Island, New Zealand, as indicated by a study of 

Sr87/Sr86 ratios, and Sr, Rb, K, U, and Th abundances: Geochimica 

et Cosmochimica Acta., v. 32, no. 7, p. 699-736.

Fairbairn, H. W., Hurley, P. M., and Pinson, W. H., 1964a, Initial 

Sr^/Sr86 and possible sources of granitic rocks in southern British 

Columbia: Journal of Geophysical Research, v. 69, no. 22, p. 

4889-4893.

____1964b, Preliminary age study and initial Sr^/Sr86 of Nova Scotia 

granitic rocks by the whole-rock method: Geological Society of 

America Bulletin, v. 75, p. 253-257.

Fiske, R. S., Hopson, C. A., and Waters, A. C., 1963, Geology of Mount

Rainier National Park, Washington: U.S. Geological Survey

Professional Paper 444, 93 p. 

Gilluly, James, 1973, Steady plate motion and episodic orogeny and

magmatism: Geological Society of America Bulletin, v. 84, p.

499-514. 

Gorai, Masao, 1951, Petrologic studies on plagioclase twins: American

Mineralogist, v. 36, no. 11-12, p. 894-901. 

Grant, A. R., 1966, Bedrock geology of the Dome Peak area, Chelan,

Skagit, and Snohomish Counties, northern Cascades,

Washington: Seattle, University of Washington, Ph. D. thesis, 270

P- 

____1969, Chemical and physical controls for base metal deposition

in the Cascade Range of Washington: Washington Division of

Mines and Geology Bulletin 58, 107 p.

Hall, A., 1967, The chemistry of appinitic rocks associated with Ardara 

pluton, Donegal, Ireland: Contributions to Mineralogy and 

Petrology, v. 16, no. 2, p. 156-171.

Hamilton, Warren, 1969, Mesozoic California and the underflow of 

Pacific mantle: Geological Society of America Bulletin, v. 80, no. 

12, p. 2409-2430.

____1978, Mesozoic tectonics of the western United States, in 

Howell, D. G., and McDougall, K. A., eds., Mesozoic 

paleogeography of the western United States: Los Angeles Society 

of Economic Paleontologists and Mineralogists, Pacific section, p. 

33-70.

Hamilton, Warren, and Myers, W. B., 1967, The nature of batholiths: 

U.S. Geological Survey Professional Paper 554-C, 30 p.

Hedge, C. E., Hildreth, R. A., and Henderson, W. T., 1970, Strontium 

isotopes in some Cenozoic lavas in Oregon and Washington: Earth 

and Planetary Science Letters, v. 8, no. 6, p. 434-438.

Hedge, C. E., and Walthall, F. G., 1963, Radiogenic strontium-87 as an 

index of geologic processes: Science, v. 140, no. 3572, p. 1214-1217.

Hess, H. H., 1939, Extreme fractional crystallization of a basaltic 

magma; the Stillwater igneous complex (abs.): American 

Geophysical Union Transactions, pt. 3, p. 430-432.

____1960, The Stillwater igneous complex, Montana A quantitative mineralogical study: Geological Society of America 

Memoir 80, 230 p.

Hietanen, Anna, 1975, Generation of potassium-poor magmas in the 

northern Sierra Nevada and the Svencofennian of Finland: U.S. 

Geological Survey Journal of Research, v. 3, no. 6, p. 631-645.

Hopson, C. A., 1964, The crystalline rocks of Howard and Montgomery 

Counties, in The geology of Howard and Montgomery Counties: 

Baltimore, Maryland Geological Survey, p. 27-215.

Hunt, C. B., 1938, A suggested explanation of the curvature of columnar joints in volcanic necks: American Journal of Science, 5th ser., 

v. 36, no. 212, p. 142-149.

Hurley, P. M., Bateman, P. C., Fairbairn, H. W., and Brannock, W. 

W., 1965, Investigation of initial Sr^/Sr86 ratios in the Sierra 

Nevada plutonic province: Geological Society of America Bulletin, v. 76, no. 2, p. 165-174.

Hurley, P. M., Hughes, H., Faure, G., Fairbairn, H. W., and Pinson, 

W. H., 1962, Radiogenic strontium-87 model of continent formation: Journal of Geophysical Research, v. 67, no. 13, p. 5315-5334.

Irvine, T. N., 1967, The ultramafic rocks of the Muskox intrusion, 

Northwest Territories, Canada, in Wyllie, P. J., ed., Ultramafic 

and related rocks: New York and London, John Wiley and Sons, p. 

38-49.

Jackson, E. D., 1961, Primary textures and mineral associations in the 

ultramafic zone of the Stillwater complex, Montana: U.S. 

Geological Survey Professional Paper 358, 106 p. 

.1967, Ultramafic cumulates in the Stillwater, Great Dyke, and

Busveld intrusions, in Wyllie, P. J., ed., Ultramafic and related

rocks: New York and London, John Wiley and Sons, p. 20-38. 

Jahns, R. H., and Burnham, C. W., 1958, Melting and crystallization

of granite and pegmatite [pt. 2] of Experimental studies of

pegmatite genesis (abs.): Geological Society of America Bulletin,

v. 69, no. 12, p. 1592-1593. 

James, A.V.G., 1920, Factors producing columnar structures in lavas

and its occurrence near Melbourne Australia: Journal of Geology,

v. 28, no. 5, p. 458-469. 

Johannsen, Albert, 1937, The intermediate rocks, v. 3 o/A descriptive

petrography of the igneous rocks: Chicago, University of Chicago

Press, 360 p. 

Kennedy, G. C., 1953, Geology and mineral deposits of the Jumbo

Basin, southeastern Alaska: U.S. Geological Survey Professional

Paper 251, 46 p. 

____1955, Some aspects of the role of water in rock melts, in Poldervaart, Arie, ed., Crust of the earth A symposium: Geological

Society of America Special Paper 62, p. 489-503.

Lane, A. C., 1931, Size of batholiths: Geological Society of America

Bulletin, v. 42, no. 3, p. 813-824. 

Larsen, E. S., Irving, John, Gonyer, F. A., and Larsen, E. S., 3rd, 1938,

Petrologic results of a study of the minerals from the Tertiary

volcanic rocks of the San Juan Region, COLORADO: American

Mineralogist, v. 23, no. 7, p. 417-429. 

Luth, W. C., Jahns, R. H., and Tuttle, O. F., 1964, The granite system

at pressures of 4 to 10 kilobars: Journal of Geophysical Research,

v. 69, no. 4, p. 759-773. 

Mattinson, J. M., 1972, Age of zircons from the northern Cascade

Mountains, Washington: Geological Society of America Bulletin,

v. 83, no. 12, p. 3769-3784. 

McTaggart, K. C., and Thompson, R. M., 1967, Geology of part of the

northern Cascades in southern British Columbia: Canadian Journal of Earth Science, v. 4, no. 6, p. 1199-1228. 

Misch, P. H., 1952, Geology of the Northern Cascades of Washington:

Mountaineer, v. 45, no. 12, p. 4-22. 

____1966, Tectonic evolution of the Northern Cascades of

Washington State A west-cordilleran case history, in A symposium on the tectonic history and mineral deposits of the western 

Cordillera, Vancouver, B.C., 1964: Canadian Institute of Mining 

and Metallurgy Special Volume 8, p. 101-148.

Modreski, P. J., and Boettcher, A. L., 1972, The stability of 

phlogopite+enstatite at high pressures A model for micas in the 

interior of the Earth: American Journal of Science, v. 272, no. 9, p. 

852-869.

Moehlman, R. S., 1948, Discussion, in Gilluly, James, chairman, 

Origin of granite: Geological Society of America Memoir 28, p. 

117-118.

Morrison, M. E., 1954, Petrology of the Phelps Ridge-Red Mountain 

area, Chelan County, Washington: Seattle, University of 

Washington M.S. thesis, 95 p.
104 INTRUSIVE ROCKS, HOLDEN AND LUCERNE QUADRANGLES, WASHINGTON

Nockolds, S. R., 1954, Average chemical compositions of some igneous

rocks: Geological Society of America Bulletin, v. 65, no. 10, p.

1007-1032. 

Orville, P. M., 1963, Alkali ion exchange between vapor and feldspar

phases: American Journal of Science, v. 261, no. 3, p. 201-237. 

Peterman, Z. E., Carmichael, I.S.E., and Smith, A. L., 1970, Sr'YSr86

ratios of Quarternary lavas of the Cascade Range, northern

California: Geological Society of America Bulletin, v. 81, no. 1, p.

311-318. 

Pitcher, W. S., and Berger, A. R., 1972, The geology of Donegal; a

study of granite emplacement and unroofing: New York, WileyInterscience, 435 p. 

Ragan, D. M., 1963, Emplacement of the Twin Sisters dunite,

Washington: American Journal of Science, v. 261, no. 6, p.

549-565.

Reynolds, D. L., 1954, Fluidization as a geological process and its bearing on the problem of intrusive granites: American Journal of

Science, v. 252, no. 10, p. 577-614. 

Richarz, Stephen, 1933, Peculiar gneisses and ore formations in the

eastern Cascades, Washington: Journal of Geology, v. 41, no. 7, p.

757-768.

Shawe, D. R., and Parker, R. L., 1967, Mafic-ultramafic layered intrusion at Iron Mountain, Fremont County, Colorado: U.S.

Geological Survey Bulletin 1251-A, p. A1-A29. 

Silberman, N. J., and McKee, E. H., 1971, K-Ar ages of granitic

plutons in north-central Nevada: Isochron/West, no. 1, p. 15-32. 

Smith, J. V., 1958, The effect of temperature, structural state, and

composition on the albite, pericline, and acline-A twins of

plagioclase feldspars: American Mineralogist, v. 43, nos. 5-6, p.

546-551. 

Southwick, D. L., 1974, Geology of the Alpine-type ultramafic complex

near Mount Stuart, Washington: Geological Society of America

Bulletin, v. 85, no. 3, p. 391-402. 

Staatz, M. H., Tabor, R. W., Weis, P. L., Robertson, J. F., VanNoy, R.

M., and Pattee, E. C., 1972, Geology and mineral resources of the

northern part of the North Cascades National Park, Washington:

U.S. Geological Survey Bulletin 1359, 132 p. [1973]. 

Tabor, R. W., 1958, The structure and petrology of a portion of the

Magic-Formidable region in the northern Cascades, Washington:

Seattle, University of Washington M.S. thesis. 

 1963, Large quartz diorite dike and associated explosion breccia,

northern Cascade Mountains, Washington: Geological Society of

American Bulletin, v. 74, no. 9, p. 1203-1208. 

Tabor, R. W., and Crowder, D. F., 1969, On batholiths and volcanoes:

U.S. Geological Survey Professional Paper 604, 67 p. 

Taubeneck, W. H., 1967, Petrology of Cornucopia tonalite, Cornucopia

stock, Wallowa Mountains, northeastern Oregon: Geological

Society of America Special Paper 91, 56 p. 

Taylor, S. R., and White, A.J.R., 1966, Trace element abundances in

andesites [with discussion]: Bulletin Volcanologique, v. 29, p.

177-194. 

Troger, W. E., 1967, Optische Bestimmung der gesteinsbildenden

Minerale, Teil 2, Testband: Stuttgart, E. Schweizerbartsche

Verlagabuchhandlung, 822 p.

Turner, F. J., 1951, Observations on twinning of plagioclase in

metamorphic rocks: American Mineralogist, v. 36, nos. 7-8, p.

581-589. 

Tuttle, O. F., and Bowen, N. L., 1958, Origin of granite in the light of

experimental studies in the system NaAlSi 3 O 8 -

KAlSi:iO8-SiO2-H2O: Geological Society of America Memoir 74,

153 p. 

Vance, J. A., 1961, Polysynthetic twinning in plagioclase: American

Mineralogist, v. 46, nos. 9-10, p. 1097-1119. 

____1962, Zoning in igneous plagioclase Normal and oscillatory

zoning: American Journal of Science, v. 260, no. 10, p. 746-760. 

____1965, Zoning in igneous plagioclase Patchy zoning: Journal of

Geology, v. 73, no. 4, p. 636-651. 

_1978, The pre-Yakima basement of the Washington Cascades:

Rockwell Hanford Operation Basalt Isolation Program, Tectonics 

and Seismicity of the Columbia Plateau workshop, Seattle, 

Wash., 6 p.

Van Diver, B. B., 1967, Contemporaneous faulting Metamorphism in 

Wenatchee Ridge area, Northern Cascades, Washington: 

American Journal of Science, v. 265, no. 2, p. 132-150.

Wager, L. R., and Deer, W. A., 1939, The petrology of the Skaergaard 

intrusion, Kanglrdlugssnaq, East Greenland: Meddelelser <j>m 

Gr^nland, v. 105, no. 4, 346 p.

Walker, G. P. L., and Skelhorn, R. R., 1966, Some associations of acid 

and basic igneous rocks: Earth-Science Reviews, v. 2, no. 2, p. 

93-109.

Waters, A. C., 1932, A petrologic and structural study of the Swakane 

gneiss, Entiat Mountains, Washington: Journal of Geology, v. 40, 

no. 6, p. 604-633.

____1960, Determining direction of flow in basalts: American Journal of Science, v. 258-A (Bradley Volume), p. 350-366.

Whetten, J. T., 1976, Tertiary sedimentary rocks in the central part of 

the Chiwaukum graben, Washington (abs.): Geological Society of 

America Abstracts with Programs, v. 8, no. 3, p. 420.

Willis, C. L., 1953, The Chiwaukum graben, a major structure of 

central Washington: American Journal of Science, v. 251, no. 11, 

p. 789-797.

Yeats, R. S., and Engels, C., 1971, Potassium-argon ages of plutons in 

the Skykomish-Stillaguamish areas, North Cascades, 

Washington, in Geological Survey research 1971: U.S. Geological 

Survey Professional Paper 750-D, p. D34-D38.

Yoder, H. S., Jr., 1969, Calcalkalic andesites Experimental data 

bearing on the origin of their assumed characteristics, in Andesite 

Conference, Eugene and Bend, Ore., 1968, Proceedings, Oregon 

Department of Geology and Mineral Industries Bulletin 65, p. 

77-89.

____1973, Contemporaneous basaltic and rhyolitic magmas: 

American Mineralogist, v. 58, p. 153-171.

Yoder, H. S., Jr., and Tilley, C. E., 1962, Origin of basaltic 

magmas An experimental study of natural and synthetic rock 

systems: Journal of Petrology, v. 3, pt. 3, p. 342-532.

Youngberg, E. A., and Wilson, T. H., 1952, The geology of the Holden 

mine: Economic Geology, v. 47, p. 1-12.
INDEX

[Italic page numbers indicate major references]

Actinolite ................................. 57, 59

Rock Creek ......................... ..... 60

DuncanHill Pluton......................... 65

Age. ........................... .3,7,23,56,58,93

Sulphur Mountain pluton .................... 37

Swakane Biotite Gneiss ...................... 5

Agmatite, Duncan Hill pluton ................... 65

Alaskite .................................. 58, 60

Albite .............................. 56, 59, 84, 89

Buck Creek pluton ........................ 39

Clark Mountain stocks ...................... 53

Cloudy Pass batholith ..................... 87

Duncan Hill pluton ......................... 64

High Pass pluton .......................... 39

Old Gib volcanic rocks ...................... 74

Allanite...... ......................... 57, 76,84

Cardinal Peak pluton ...................... 50

Duncan Hill pluton ......................... 61

Railroad Creek pluton....................... 79

Rampart Mountain pluton ................... 71

Alpine Creek. ............................ 38, 92

Amphibole ................. ................. 81

See also Hornblende. 

Amphibolite.................................. 96

Andesine ......................... 56, 59,60, 76, 84

Bearcat Ridge pluton .................... 18,19

Cardinal Peak pluton .................... 48, 50

Clark Mountain stock....................... 53

Cloudy Pass batholith ...................... 87

Dumbell Mountain pluton ................ 10,11

Duncan Hill pluton ................... 62,67, 99

Entiat pluton.............................. 26

Larch Lakes pluton ......................... 69

Leroy Creek pluton ......................... 22

Old Gib volcanic rocks ...................... 74

Rock Creek ......................... ..... 60

Seven-fingered Jack pluton .................. 25

Tenpeakpluton ...... .................. 33,34

White Mountain pluton .................... 34

Anorthite ................................. 34,67

Anthem Creek ................................ 83

Antigorite................................... 7, 8

Apatite ........................ 8, 57, 59,60, 76, 84

Bearcat Ridge pluton ....................... 19

Buck Creek pluton ......................... 39

Cardinal Peak pluton ....................... 50

Clark Mountain............................ 53

Dumbell Mountain pluton .............. ... 11

Duncan Hill pluton ........................ 61

Entiat pluton........................... 25, 26

High Pass pluton .......................... 39

Holden Lake pluton ........................ 81

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Railroad Creek pluton. ..................... 78

Rampart Mountain pluton ..... ............. 71

Riddle Peaks pluton ....................... 43

Rock Creek ............................... 60

Seven-fingered Jack pluton ............ ..... 27

Swakane Biotite Gneiss ..................... 29

Tenpeak pluton............................ 34

White Mountain pluton ..................... 34

Aplite, Duncan Hill pluton ...................... 64

Page

Appinite..... .... ............. ............ 90

Archean Stillwater Complex..................... 44

Augite. . .............................. .59, 85

Cloudy Pass batholith ..................... 88

See also Pyroxene.

B

Basalt Peak .................................. 72

Bear Creek ................................ 18,77

Bearcat Ridge pluton ........... . . . 18, 77,89, 92, 97

Big Creek ..................................... 9

Biotite ............ 5,8, 56, 58, 59, 75, 76, 82, 84, 89, 97

Bearcat Ridge pluton ..... ............. 19,20

Buck Creek pluton ......... ............... 39

Cardinal Peak pluton. .......... .46,47,48,50,51

Clark Mountain............................ 53

Cloudy Pass batholith ..... ................ 87

Copper Peak pluton ........................ 81

Dumbell Mountain pluton ............. 10,11,17

Duncan Hill pluton ................ 61,62, 64, 99

Entiat pluton .......... ....... 24,25, 26, 27, 29

High Pass pluton .......................... 39

Holden Lake pluton ........................ 81

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Old Gib volcanic rocks ...................... 74

Railroad Creek pluton....................... 78

Rampart Mountain pluton ................... 71

Riddle Peaks pluton ........................ 43

Rock Creek ............................... 60

Seven-fingered Jack pluton...... .24, 25, 26, 27,29

Sulphur Mountain pluton .................... 37

Tenpeakpluton ...................... 32,33,34

White Mountain pluton ............... 32, 33, 34

Biotite dacite ................................. 84

Biotite granodiorite ... ........................ 83

Cardinal Peak pluton............ ........ 46, 47

Duncan Hill pluton ......................... 99

High Pass pluton .......................... 37

Larch Lakes pluton......................... 68

Rampart Mountain pluton ................... 70

Black Peak batholith........................... 96

Bonanza Peak ................................ 11

Boulder Creek ................................. 7

Buck Creek plutons ......................... 37, 92

Buck Mountain ............................... 37

Buckskin Mountain ....................... 7, 61, 83

Bytownite. ................................ .8, 59

Cloudy Pass batholith ...................... 87

Duncan Hill pluton ...................... 65, 99

Riddle Peaks pluton ........................ 43

Calcite. . ............................. 35, 59, 60

Buck Creek pluton ........................ 39

High Pass pluton ......................... 39

Cardinal Peak............ .................... 47

Cardinal Peak pluton ......... 18, 40, 46, 75, 82, 84, 92

Cascade River Schist....................... 8,101

Cascadia ................................... 3, 91

Chalcopyrite, Cloudy Pass batholith .............. 89

Page

Chelan Complex ................... 3,10, 23, 96, 101

Chelan Lake. See Lake Chelan.

Chiwaukum graben ........... 5,6,7, 58, 72,84,92, 98

Chiwawa Ridge ............................ 29, 38

Chiwawa River................................ 58

Chiwawa River valley .......................... 72

Chlorite ........................... 8, 57, 59,60,83

Bearcat Ridge pluton ....................... 19

Buck Creek pluton ......................... 39

Cardinal Peak pluton ...................... 50

Clark Mountain stocks ...................... 53

Cloudy Pass batholith ...................... 87

Dumbell Mountain pluton ................... 11

Duncan Hill pluton ......................... 62

Entiat pluton ..................... 25, 26, 27, 29

High Pass pluton .......................... 39

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Old Gib volcanic rocks ...................... 74

Railroad Creek pluton ......................78

Rampart Mountain pluton ................... 71

Riddle Peaks pluton ........................ 43

Rock Creek ............................... 60

Seven-fingered Jack pluton. ........ .25, 26, 27, 29

Sulphur Mountain pluton................... 37

Tenpeak pluton............................ 35

White Mountain pluton ..................... 35

Clark Mountain stocks ................. 53, 92, 96, 98

Clinopyroxene ........................... 8,60,83

Cardinal Peak pluton ....................... 50

Cloudy Pass batholith ...................... 87

Sulphur Mountain pluton .................... 37

Clinozoisite................................. 5, 57

Buck Creek pluton ......................... 39

Cardinal Peak pluton ....................... 50

Clark Mountain stocks ...................... 53

Dumbell Mountain pluton ................... 11

Entiat pluton........................... 25, 26

High Pass pluton .......................... 39

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Railroad Creek pluton.................... 78, 79

Seven-fingered Jack pluton ............... 25, 26

Sulphur Mountain pluton.................... 37

Tenpeak pluton............................ 34

White Mountain pluton ..................... 34

Cloudy Pass batholith ........ 17, 53,60,67,68, 72,80,

85, 86, 91, 92, 98

Coast Range batholith complex ................... 4

Columbia River ............................. 5, 30

Columbia River plateau.......................... 4

Contact complexes .......................... 27, 90

Cardinal Peak pluton ....................... 49

Copper Peak pluton ........................ 90

Duncan Hill pluton ................... 61,65,90

Holden Lake pluton ........................ 90

Seven-fingered Jack pluton ............... 49,90

Tenpeak pluton ............................ 34

White Mountain pluton. .............. .34, 49,90

Copper Peak ................................ 9, 81

Copper Peak pluton ......................... 80, 90

Cordillera .................................... 91

Cottonwood Guard Station ................ 17,61,62

105
106 INDEX

Page

Crow Hill .................................... 85

Custer Gneiss.................................. 5

Custer Granite Gneiss ........................... 5

Cutler Formation............................... 6

D

Dacite, Old Gib volcanic neck .................... 72

Dikes........................................58

Diorite ...................................... 90

Copper Peak pluton ........................ 81

Duncan Hill pluton ......................... 61

Dole Creek ........................ .......... 47

DomkeLake................ ................. 77

Donegal pluton ........................... ... 81

Dumbell Mountain plutons ........ 8, 23, 25, 30,91, 92

96, 98, 100, 101 

Duncan Hill pluton............ 8,17, 54,56, 57, 58, 61,

81, 82, 85, 89, 91, 92, 97 

contact complexes .................... 61, 65, 90

pawdite .................................. 59

E

Edil mine .................................... 43

Bllicott City Granodiorite, Maryland ............. 35

Emerald Peak................................ 50

Entiat fault................................ 25, 72

Entiat Meadows ..................... ........ 75

Entiat Mountains ............................. 20

Entiat pluton ............ 10, 23, 41,58,68, 70, 96, 101

Entiat River ........................... 17, 48, 61

Epidote ........................ 5, 57, 59,60,84,89

Bearcat Ridge pluton ....................... 19

Buck Creek pluton ......................... 39

Cardinal Peak pluton ....................... 50

Clark Mountain stocks ...................... 53

Dumbell Mountain pluton ................... 11

Entiat pluton ..................... 25, 26, 27, 29

High Pass pluton .......................... 39

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Railroad Creek pluton....................... 78

Rampart Mountain pluton ................... 71

Riddle Peaks pluton ..................... . . 43

Seven-fingered Jack pluton......... 25, 26, 27, 29

Sulphur Mountain pluton.................... 37

Tenpeak pluton ............................ 34

White Mountain pluton ..................... 34

Feldspar .................................. 59,83

Buck Creek pluton ..... ................... 37

Duncan Hill pluton ......................... 64

Fern Lake .......................... 61, 62, 67, 82

Flaser gneiss..................................33

Fourth of July Basin ........................ 45, 46

G

Gabbro ................................ 26, 32,90

Copper Peak pluton ........................ 81

Duncan Hill pluton ......................... 65

Garland Peak ........................... 58,85,86

Garnet ....................................... 5

Buck Creek pluton ........................ 39

High Pass pluton ...................... . . 39

Leroy Creek pluton ......................... 22

Tenpeak pluton ...................... 33, 34,35

White Mountain pluton ............... 33,34, 35

Glacier Creek ................................. 87

Glacier Peak quadrangle ........... 3, 7,31, 60,86, 98

Glacier Peak volcano ........................... 31

Gopher Mountain ............................. 83

Graham Harbor Creek.......................... 19

Granite, Duncan Hill pluton .................. . . 64

Page

Granodiorite............................ 59,60,82

Bearcat Ridge pluton ....................... 19

Cardinal Peak pluton .................... 47, 50

Clark Mountain stocks ................. 53, 54

Cloudy Pass batholith ..................... 86

Copper Peak pluton ........................ 81

Dumbell Mountain pluton ................... 18

Duncan Hill pluton ...................... 61, 62

Entiat pluton. .......................... 28, 29

High Pass pluton........................ 38, 40

Larch Lakes pluton. ....................... .69

Railroad Creek pluton....................... 77

Rampart Mountain pluton ................... 70

Seven-fingered Jack pluton ............... 28, 29

Sulphur Mountain pluton.................... 37

Tenpeak pluton ............................ 32

White Mountain pluton ......... .......... 32

Granophyre................ ................ 84

Cloudy Pass batholith ...................... 87

Duncan Hill pluton ......................... 64

H

Hart Lake ....................... 23, 25, 86, 87, 93

Helmet Butte................................ 38

High Pass pluton ..................... 37, 92, 97

HoldenLake. ................................ .81

Holden Lake pluton ............................ 80

contact complexes.......................... 90

Holden mine ................... 3, 7, 8, 56, 75, 81, 83

Hope, British Columbia.......................... 3

Hope fault .................................... 4

Hornblende. ........ 5,6,8, 56,58, 59,60, 75, 76,82,98

Bearcat Ridge pluton .................... 19, 20

Buck Creek pluton .... .................... 39

Cardinal Peak pluton ............ 46, 47, 48, 50, 51

Clark Mountain stocks ...................... 53

Cloudy Pass batholith ..................... 87

Copper Peak pluton ........................ 81

Dumbell Mountain pluton.............. 10, 11,17

Duncan Hill pluton ................ 61, 62, 64,99

Entiat pluton........................ 24, 25, 26

High Pass pluton .......................... 39

Holden Lake pluton .............. ........ 81

Leroy Creek pluton ......................... 22

Old Gib volcanic rocks ...................... 74

Railroad Creek pluton....................... 77

Riddle Peaks pluton ..................... 41, 51

Rock Creek .............................. 60

Seven-fingered Jack pluton. ........... .24, 25,26

Sulphur Mountain pluton.................... 37

Tenpeak pluton ...................... 32,33, 34

White Mountain pluton ............... 32, 33, 34

Hornblendediorite............................ .26

Cardinal Peak pluton................. .46,48, 50

Rock Creek............................... .60

Hornblende gabbro, Duncan Hill pluton ........... 61

Hornblendite ............................ 7,8, 90

Cardinal Peak pluton ....................... 49

Copper Peak pluton ........................ 81

Duncan Hill pluton ...................... 61, 65

Entiat pluton. .......................... 24, 27

Riddle Peaks pluton ........................ 50

Seven-fingered Jack pluton ............... 24, 27

Tenpeak pluton ......................... 32, 34

White Mountain pluton ..................... 32

Hypersthene, Cloudy Pass batholith .............. 87

I

IceCreek ............. .................. 9,17, 23

Ice Lake ..................................... 25

Idaho batholith ............................... 91

Ilmenite ................................... 8,57

Bearcat Ridge pluton ....................... 19

Duncan Hill pluton ......................... 61

Iron sulflde................................... 43

K Page

Kersantite. ................................58, 59

King Lake....................................38

KloneCreek ............................ 18, 48, 75

Kyanite....................................... 5

Labradorite. ...................... .8,56,60,76,90

Cardinal Peak pluton ....................... 51

Cloudy Pass batholith. ................86,87,98

Dumbell Mountain pluton ................... 11

Duncan Hill pluton ..................... 65, 99

Holden Lake pluton . ...................... 81

Old Gib volcanic rocks ...................... 73

Riddle Peaks pluton .................. . . 43,44

LakeChelan ............................ 18, 77,84

Lamprophyre, Duncan Hill pluton ................ 64

Larch Lakes .............................. 27,70

Larch Lakes pluton. ............... .56,58,681 70,85

Leroy Creek pluton ....... 9,10,20, 23,96,97,100,101

Limonite..................................... 89

Little Creek .................................. 77

Lucerne Mountain............................. 77

M

Magnetite ....................... 7, 8, 57, 59, 60, 89

Bearcat Ridge pluton ....................... 19

Cardinal Peak pluton ....................... 51

Clark Mountain stocks ...................... 53

Dumbell Mountain pluton ................... 11

Duncan Hill pluton ......................... 61

Entiat pluton........................... 26, 27

Holden Lake pluton ........................ 81

Old Gib volcanic rocks ...................... 74

Rampart Mountain pluton ................... 71

Riddle Peaks pluton ........................ 43

Seven-fingered Jack pluton ............... 26, 27

Marble .................................... 6, 43

Marble Meta Quartz Diorite .................. 8,101

Marblemount belt .......................... 23, 96

Methow trough ................................ 3

Mica ...................................... 6, 20

Microcline.................................... 59

Bearcat Ridge pluton ....................... 19

Buck Creek pluton ......................... 39

Clark Mountain............................ 53

Entiat pluton.............................. 29

High Pass pluton .......................... 39

Larch Lakes pluton......................... 69

Railroad Creek pluton. ...................... 79

Rampart Mountain pluton ................... 71

Seven-fingered Jack pluton .................. 29

Sulphur Mountain pluton.................... 37

Tenpeak pluton............................ 34

White Mountain pluton ..................... 34

Migmatite.............................. 22, 28,58

Milham Pass............................ 47, 84,85

Miners Ridge ................................. 86

Minette, augite............................. 58, 59

Mirror Lake ............................... 77,89

Mordenite.................................... 65

Mount Fernow................................ 11

Mount Rainier National Park .................... 87

Mount Stuart batholith........................ 96

Muscovite................. ................. 84

Bearcat Ridge pluton ....................... 19

Duncan Hill pluton ......................... 62

Entiat pluton. ...................... .26, 27, 29

Leroy Creek pluton ......................... 22

Railroad Creek pluton....................... 79

Rampart Mountain pluton ................... 71

Seven-fingered Jack pluton ........... 26, 27, 29

Tenpeak pluton............................ 34

White Mountain pluton ..................... 34

Mylonite..................................... 57
INDEX 107

Myrmekite ................................ 76, 84

Bearcat Ridge pluton ....................... 19

Clark Mountain stocks ...................... 53

High Pass pluton .......................... 39

Railroad Creek pluton....................... 79

Rampart Mountain pluton ................... 71

Tenpeak pluton .......... .......... ...... 35

White Mountain pluton ..................... 35

N

Napeequa River ............................. 6,38

Ninemile Creek ....................... 41, 75, 77, 82

Nontronite .................. .... ....... 85

Cloudy Pass batholith ..................... 89

Old Gib volcanic rocks ...................... 74

North Fork, Entiat River . ............... ..... 61

North Star Mountain........................... 86

O

Okanogan terrain............................... 3

Old Gib Mountain .............. .............. 72

Old Gib volcanic neck. ................ .60, 72, 74, 85

Old Gib volcanic rocks ....................... 72, 85

Oligoclase ........................... 56, 60, 84,89

Bearcat Ridge pluton ................... ... 19

Buck Creek pluton ......................... 39

Cardinal Peak pluton .... .................. 48

Clark Mountain stocks ..................... 53

Cloudy Pass batholith ..................... 87

Duncan Hill pluton ......................... 62

Entiat pluton......................... 26, 29

High Pass pluton .......................... 39

Leroy Creek pluton ......................... 22

Rampart Mountain pluton ......... ......... 71

Seven-fingered Jack pluton ............... 26, 29

Sulphur Mountain pluton.................... 37

Olivine.............................. .... 7, 8, 45

Opaque minerals ....................... ...... 57

Buck Creek pluton .................. ...... 39

Cardinal Peak pluton ....................... 50

Duncan Hill pluton ......................... 62

Entiat pluton........................... 25, 29

High Pass pluton ......................... 39

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Railroad Creek pluton....................... 78

Seven-fingered Jack pluton ............... 25, 29

Tenpeak pluton ........................... 34

White Mountain pluton . ................... 34

Orthoclase ............................ 59,76,83

Bearcat Ridge pluton ...... ......... ...... 19

Buck Creek pluton ......................... 39

Cardinal Peak pluton ....................... 50

Cloudy Pass batholith.................. 87,98

Duncan Hill pluton.................. ...... 62

Entiat pluton.............................. 27

High Pass pluton .......................... 39

Holden Lake pluton ........................ 81

Larch Lakes pluton......................... 69

Riddle Peaks pluton . ..... ............. 43

Rock Creek .............................. 60

Seven-fingered Jack pluton .................. 27

Orthopyroxene................................. 8

Pawdite ................................ 58, 60,68

Pegmatite.................................... 38

Pelean spine, Old Gib volcanic neck ............. .73

Penninite ................................. 57, 72

Pentlandite................................. . . 8

Pericline ..................................... 56

Peridotite ............................ 7, 8,45, 90

Perthite................................ 19, 83, 89

Duncan Hill pluton......................... 62

Phelps Creek ................................ 20

Phelps Ridge ............................... 5, 86

Phlogopite ............................ 8, 56, 97

Picotite....................................... 7

Plagioclase ................. 8, 56, 57, 59, 76, 83, 90

Bearcat Ridge pluton ....................... 19

Clark Mountain stocks .... ................. 53

Cloudy Pass batholith. .................. .87,98

Dumbell Mountain pluton ........... 10,11,17

Duncan Hill pluton ..................... 62, 67

Entiat pluton........................... 25, 27

Holden Lake pluton ........................ 81

Old Gib volcanic rocks ........ ............. 74

Railroad Creek pluton...................... 78

Riddle Peaks pluton ........................ 43

Seven-fingered Jack pluton ............... 25,27

Tenpeak pluton............................ 34

White Mountain pluton ..................... 34

PomasCreek............................... 27, 29

Potassium feldspar.............. 54, 56,60, 76, 84,97

Bearcat Ridge pluton ...................... 20

Buck Creek pluton ......................... 39

Cardinal Peak pluton ....................... 47

Clark Mountain stocks..................... 53

Cloudy Pass batholith .................... .98

Dumbell Mountain pluton ............. ..... 11

Duncan Hill pluton ........................ 62

Entiat. pluton.............................. 29

High Pass pluton .......................... 39

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Railroad Creek pluton...................... 78

Rampart Mountain pluton ................... 71

Seven-fingered Jack pluton .................. 29

Tenpeak pluton............................ 34

White Mountain pluton ..................... 34

Prehnite, Buck Creek pluton. ................... .39

High Pass pluton .......................... 39

Old Gib volcanic rocks ...................... 74

Riddle Peaks pluton ........................ 43

Pyramid Creek................................ 61

Pyramid Mountain ............................ 47

Pyrite ................................. 59, 83, 89

Cloudy Pass batholith ...................... 87

Railroad Creek pluton. ...................... 78

Riddle Peaks pluton ........................ 43

Pyroxene .................................. 8,99

Old Gib volcanic rocks ...................... 74

Riddle Peaks pluton ....................... 45

Pyrrhotite.............................. ... 8, 89

Q

Quartz ............... 5, 56, 58, 59, 60, 76, 83, 84, 89

Bearcat Ridge pluton .............. ........ 19

Buck Creek pluton. .................... .37, 39

Cardinal Peak pluton ....................... 50

Clark Mountain stocks ...................... 53

Cloudy Pass batholith ........... ......... 87

Dumbell Mountain pluton ............ 10,11,17

Duncan Hill pluton......................... 62

Entiat pluton ....... ............. 25, 26, 27, 29

High Pass pluton .............. ........... 39

Holden Lake pluton ........................ 81

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Old Gib volcanic rocks ...................... 74

Railroad Creek pluton....................... 78

Rampart Mountain pluton ................... 71

Riddle Peaks pluton ........................ 43

Rock Creek ............................... 60

Seven-fingered Jack pluton.......... 25, 26, 27, 29

Sulphur Mountain pluton.................... 37

Tenpeak pluton............................ 34

White Mountain pluton ..................... 34

Quartz diorite. .......... .5,7,56,58,60,7582,90,98

Bearcat Ridge pluton .................... 19, 20

Cardinal Peak pluton ............ 46,47, 48, 50, 51

Clark Mountain stocks ................... 53,54

Cloudy Pass batholith ...................... 87

Dumbell Mountain pluton ......... 9,10, 11,17, 18

Duncan Hill pluton ...................... 61, 64

Entiat pluton ....... ............ 24,25,2ft 28

High Pass pluton. ...................... .37,40

Larch Lakes pluton......................... 69

Leroy Creek pluton ......................... 22

Railroad Creek pluton....................... 78

Riddle Peaks pluton ........................ 43

Seven-fingered Jack pluton ......... .24, 25,26, 28

Tenpeak pluton ...................... 32,33, 34

White Mountain pluton. .............. .32, 33, 34

Quartz gabbro. Cloudy Pass batholith............. 86

Copper Peak pluton ........................ 81

Holden Lake pluton ........................ 81

Quartz granodiorite ......................... 58, 75

Quartz latite ..... ...........................84

Quartzmonzonite ......... 56,58, 59, 60, 75,,82, 83, 89

Cloudy Pass batholith ...................... 98

Copper Peak pluton ........................ 81

Duncan Hill pluton ...................... 62,99

Larch Lakes pluton......................... 69

Railroad Creek pluton. ..................... .78

Rampart Mountain pluton ................ 70, 71

Riddle Peaks pluton ........................ 43

Quartzite ..............................6. 34, 43

Railroad Creek ..................... 9,10,18, 40, 47

Railroad Creek pluton ..... 46, 56,57, 58, 76, 77, 84,92

Rampart Mountain ......................... 58, 70

Rampart Mountain pluton.......... 56,57,58, 70, 85

Red Mountain ................................. 3

Rhyodacite ................................ 58,84

Rhyolite ..................................... 61

Riddle Creek. .............................79,84

Riddle Peaks ........................ 77, 83,91, 92

Riddle Peaks pluton ............. 40, 45,50,51,65, 75

Ripidolite ................................. 43, 44

Rock Creek .......................... 20,29, 60, 86

Ross Lake fault ................................ 4

Saska Peak................................... 47

Sausurite, Duncan Hill pluton ................... 62

Seriate ........................... . 57, 59, 60, 89

Buck Creek pluton ......................... 39

Cardinal Peak pluton ....................... 50

Clark Mountain............................ 53

Dumbell Mountain pluton ................... 11

Entiat pluton. ...................... .25,27, 29

High Pass pluton ......................... 39

Larch Lakes pluton..... ................... 69

Leroy Creek pluton ........................ 22

Railroad Creek pluton ..................... .78

Rampart Mountain pluton ................... 71

Riddle Peaks pluton ........................ 43

Rock Creek ............................... 60

Seven-fingered Jack pluton ............ 25, 27, 29

Sulphur Mountain pluton.................... 37

Tenpeak pluton............................ 35

White Mountain pluton ..................... 35

Serpentine ............... ................. 7, 45

Seven-fingered Jack pluton....... 10,17, 20,23, 26,41,

49, 92, 96, 100 

contact complexes....................... 49,90

Sevenmile Creek drainage ....................... 82

Shetipo Creek.................................27

Sierra Nevada batholith .................. 91,93,99

Skagit Gneiss........................... 5, 30,101

See also Swakane Biotite Gneiss.
108 INDEX

Page

Skagit River................................... 5

Snoqualmie batholith ....................... 91, 93

Snow Brushy Creek ................... 46,48, 61, 67

South Pyramid Creek . . ....................... 61

Southern California batholith ................... 91

Spectacle Buttes .............................. 17

Spessartite ................................ 58,59

Sphalerite.................................... 89

Sphene. .......................... .8, 24, 33, 34, 37

Spinel ........................................ 8

Stilbite ................................... 39, 74

Stormy Mountain ............... 56, 61, 64, 67, 89, 99

Straight Creek fault. ...................... .... .4

Sulfides................................... 59, 83

Sulphur Mountain ... ......................... 37

Sulphur Mountain pluton ................. 35, 38, 97

Swakane Biotite Gneiss......... 5, 7, 22, 28, 30, 38,92,

93, 97, 98 

Swauk Formation....................... 5, 7,58, 96

Talc.

Page

Tatoosh pluton................................ 87

TenmileCreek. ...................... .42,47,75,82

Tenpeak pluton .... ......... 7, 31, 37,60, 92, 96, 98

Titanite .......................... 57, 59,60,76, 84

Bearcat Ridge pluton ....................... 19

Buck Creek pluton ........................ 39

Cardinal Peak pluton ...................... 50

Clark Mountain stocks ...................... 53

Dumbell Mountain pluton ................... 11

Duncan Hill pluton......................... 61

Entiat pluton ..... ............... 25, 26, 27, 29

High Pass pluton ......................... 39

Holden Lake pluton ........................ 81

Larch Lakes pluton. . ...................... 69

Leroy Creek pluton ......................... 22

Old Gib volcanic rocks ...... ............... 74

Railroad Creek pluton.............. ........ 78

Rampart Mountain pluton ............. ..... 71

Riddle Peaks pluton ....................... 43

Seven-fingered Jack pluton... ...... 25, 26, 27, 29

Tremolite ................................ 7,8, 59

Triad Creek ................................. 38

Trondjemite . . ............................... 28

TumbleCreek .... ..... ................... 18, 89

Page

W

White Mountain pluton ............ 31, 49,92,96,101

contact complexes.......................... 90

White River Orthogneiss. ......................32

Wilson Creek ................................. 82

X, Y, Z

Xenoliths .................................... 33

Xenotime, Duncan Hill pluton ................... 62

Yellow Aster Complex. ........................ .93

Zircon ................................. 57, 84,89

Buck Creek pluton ......................... 39

Clark Mountain............................ 53

Duncan Hill pluton ......................... 61

Entiat pluton........................... 24, 25

High Pass pluton ......................... 39

Railroad Creek pluton....................... 78

Seven-fingered Jack pluton .............. 24, 25

U.S. GOVERNMENT PRINTING OFFICE: 676-041 1982