Hetch Hetchy Reservoir Quadrangle, 

Yo semite National Park, CaliforniaAnalytic Data

GEOLOGICAL SURVEY PROFESSIONAL PAPER 774-B
Hetch Hetchy Reservoir Quadrangle, 

YoSemite National Park, CaliforniaAnalytic Data

By RONALD W. KISTLER

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 774-B

Chemical, spectro graphic, and modal analyses and 

potassium-argon age determinations on granitic 

rocks supplement Geologic Quadrangle Map GQ-1112

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1974
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 73-600259

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 Price 65 cents (paper cover)

Stock Number 2401-02462
CONTENTS

Page

Abstract .......................................................................................................................................... Bl

Introduction .................................................................................................................................. 1

Bedrock units ......................................................................................................... . .. .. 1

Analytic data.................................................................................................................................. 1

References .................................................................................................... . ................ .. 2

ILLUSTRATIONS

Page

FIGURE 1. Simplified geologic map of the Hetch Hetchy Reservoir 15-minute 

quadrangle showing locations of chemically analyzed samples 

and samples dated by potassium-argon methods ...................................... B4

2-6. Bedrock map showing 

2. Volume percent quartz ........................................................................ 6

3. Volume percent potassium feldspar .................................................. 7

4. Volume percent plagioclase ................................................................ 8

5. Volume percent mafic minerals ......................................................... 9

6. Specific gravity ..................................................................................... 10

7. Modes and norms of granitic and volcanic rocks .......................................... 11

TABLES

Page

TABLE 1. Chemical and spectrographic analyses and norms ....................................... B13

2. Potassium-argon ages.......................................................................................... 14

ill

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

HETCH HETCHY RESERVOIR QUADRANGLE, YOSEMITE NATIONAL PARK,

CALIFORNIA-ANALYTIC DATA

By RONALD W. KISTLER

ABSTRACT

Modal analyses of 226 samples and chemical analyses of 27 

samples of granitic rocks show that the average compositions of 

individual plutons range from quartz diorite to alaskite. Potassium-argon analyses of biotite and hornblende separates from 

specimens of two granitic rocks yield ages in the range of 82-96 

million years.

INTRODUCTION

The data in this paper are for use with the "Geologic 

map of Hetch Hetchy quadrangle, Yosemite National 

Park, California", U.S. Geological Survey Map GQ1112 (Kistler, 1973). The Hetch Hetchy quadrangle 

encompasses about 240 square miles in the center of 

Yosemite National Park. A single road, California State 

Highway 120, traverses the central part of the area. The 

major topographic feature in the quadrangle is the 

Grand Canyon of the Tuolumne River, which ranges 

in elevation from a little less than 4,000 feet along the 

river to more than 9,000 feet along the canyon rim. 

A dense forest, mainly on thick till and moraines 

deposited by ancient glaciers, covers about one-half of 

the quadrangle.

F. C. Calkins (1930) published a geologic map of 

part of the Yosemite Valley region that includes the 

southeast corner of the quadrangle. Calkins assigned 

relative ages to the granitic formations and described 

their petrology. F. E. Matthes (1930) discussed the 

glaciology of the Yosemite region and described in 

detail the tills and moraines along Yosemite Creek in 

the south-central part of the Hetch Hetchy quadrangle. 

The present mapping and geologic study extend the 

pioneering work of these men and is part of a continuing series of geologic investigations of bedrock geology 

of the central Sierra Nevada batholith (Bateman and 

others, 1963).

BEDROCK UNITS

Twelve major granitic formations ranging in composition from quartz diorite to alaskite constitute more

than 95 percent of the bedrock in the quadrangle (fig. 

1). Intrusive relations observed in the field and potassium-argon and rubidium-strontium dating (Curtis and 

others, 1958; Evernden and Kistler, 1970; this report) 

made it possible to assign these formations to three age 

groups. The early Cretaceous group is represented by a 

single unit of quartz diorite. In each of the Late Jurassic and Late Cretaceous groups, the oldest formation is 

quartz diorite, and the youngest is alaskite or aplite.

The oldest rocks of the quadrangle are marble, biotite-muscovite schist, and quartzite in small roof pendants. These rocks, of probable Paleozoic age, are 

complexly deformed and metamorphosed to hornblende hornfels facies. Volcanic mudflows and a trachyandesite flow of Miocene (?) and Pliocene age occur in 

isolated exposures to the north of the Grand Canyon 

of the Tuolumne River. A specimen of trachyandesite 

from Rancheria Mountain has been dated as 9 million 

years old (Pliocene) by the potassium-argon technique 

(Dalrymple, 1963).

ANALYTIC DATA

The specific gravity and modal composition of 226 

samples of granitic rock were determined. Modal analysis permits the volume percentage of the major minerals 

of a granitic rock (quartz, potassium feldspar, plagioclase, and mafic minerals) to be calculated by determining the mineral constituent present at each of 1,000- 

2,000 regularly spaced points on a sawed stained slab 

of the sample. The volume percentage of each mineral 

species is shown for each sample locality on the simplified bedrock map of the quadrangle in figures 2-5. The 

percentages were contoured by visual inspection to 

show the compositional patterns for each mineral. Specific gravities are shown in figure 6.

Chemical analyses by the rapid method of Shapiro 

and Brannock (1962) were made of 27 representative 

samples from 11 of the granitic units and of a single 

trachyandesite sample. Potassium-argon ages of biotite

Bl
B2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

and hornblende separated from samples of two of the 

granitic rocks were determined. The locations of the 

chemically analyzed and the dated samples are shown 

in figure 1. The chemical data, together with semiquantitative spectrographic analyses and CIPW norms, are 

given on table 1. The analytical data used in the age 

determinations are given on table 2.

Modes of the granitic rocks, recalculated to 100 percent, are plotted on triangular diagrams whose corners 

are quartz, plagioclase, and potassium feldspar in figure 

7. In the same figure, norms of the chemically analyzed 

samples are plotted on triangular diagrams whose 

corners are normative quartz, plagioclase (albite plus 

anorthite), and orthoclase.

REFERENCES CITED

Bateman, P. C., Clark, L. D., Huber, N. K., Moore, J. G., and 

Rinehart, C. D., 1963, The Sierra Nevada batholith a 

synthesis of recent work across the central part: U.S. Geol. 

Survey Prof. Paper 414-D, 46 p.

Calkins, F. C., 1930, The granitic rocks of the Yosemite region, 

in Matthes, F. E., ed., Geologic history of the Yosemite 

Valley: U.S. Geol. Survey Prof. Paper 160, p. 120-129.

Curtis, G. H., Evernden, J. F., and Lipson, J. I., 1958, Age 

determination of some granitic rocks in California by the 

potassium-argon method: California Div. Mines Spec. 

Rept. 54,16 p.

Dalrymple, G. B., 1963, Potassium-argon dates of some Cenozoic volcanic rocks of the Sierra Nevada, California: Geol. 

Soc. America Bull., v. 74, p. 379-390.

Evernden, J. F., and Kistler, R. W., 1970, Chronology of 

emplacement of Mesozoic batholithic complexes in California and western Nevada: U.S. Geol. Survey Prof. Paper 

623, 42 p.

Kistler, R. W., 1973, Geologic map of the Hetch Hetchy quadrangle, Yosemite National Park, California: U.S. Geol. 

Survey Geol. Quad. Map GQ-1112.

Matthes, F. E., 1930, Geologic history of the Yosemite Valley: 

U.S. Geol. Survey Prof. Paper 160,137 p.

Shapiro, Leonard, and Brannock, W. W., 1962, Rapid analyses 

of silicate, carbonate, and phosphate rocks: U.S. Geol. 

Survey Bull. 1144-A, 56 p.
FIGURES AND TABLES
B4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

119°45

+ + + + + + + + + + )

+ + + + + + + + + +/

-t- + -t- + + + -t--t--i-+/;

38°00'

;v.--.y:-.: : J37°45' 

119°30'

8 KILOMETERS

FIGURE 1. Simplified bedrock geology of the Hetch Hetchy 15-minute quadrangle and locations of chemically analyzed

samples and samples dated by potassium-argon methods.
HETCH HETCHY RESERVOIR QUADRANGLE, CALIFORNIA

EXPLANATION

B5

Pliocene Uppr Cretaceous Lower 

VJ!PVj j _i j j j j _i _i j j

Volcanic mudflows 

and trachyandesite

Hal

( 

Y

Qu 

Ta

:/:-.Kh;::.V.'-

" Dome Quartz 

Monzonite

~^^ 

^J^i\7\~

Sentinel 

jranodiorite

ill!

ffi

Dsemite Creek 

Granodiorite 

of Rose

artz diorite of 

marack Creek

Aplite

Quartz diorite of 

Mount Gibson

^

Granodiorite of Granodiorite of

Quartz diorite of 

South Fork of 

Tuolumne River

Diorite

ms mv

Metamorphic rocks 

ms, sedimentary rocks 

mv, volcanic rocks

H-40-64 

Chemically analyzed sample

H-27

Sample dated by potassium - 

argon method

80

UJ o

28

FIGURE 1. Continued
B6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

119

38°00'

37°45' 

119°30'

8 KILOMETERS

FIGURE 2. Bedrock map showing volume percent quartz.
HETCH HETCHY RESERVOIR QUADRANGLE, CALIFORNIA

 : : m ^ ^ :::V;r-\: .',;!l-H-42-69 : y

H-41-69. ' 

37°45'

119°45' 119 e 30'

8 KILOMETERS

FIGURE 3. Bedrock map showing volume percent potassium feldspar.
B8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

119°45'

38°00'

_LJ37°45'

SMILES

i

8 KILOMETERS

119 6 30'

FIGURE 4. Bedrock map showing volume percent plagioclase.
HETCH HETCHY RESERVOIR QUADRANGLE, CALIFORNIA B9

444444-444 

4-44444-44444

-+4-44444444 

4 4-4-4444444- 

S "' ;\l 4 4 4 4 4Jr 4- 4- 4 4

I: 7H 22 69 f 4- 4 4 4 4 4 4-

i-t |V *3~ 44444-444 

' / \ 4- 4 4 4 4 4 4 4- 4 4 

4\44444444+'

L\(0 -H+\;444444- 

J\N4 4 4\4 44-444,

4 4 4 4 4444 

-*- 4 4-4 444

-:^'4d;-:o^r^'x ^

n i 234567 8 KILOMETERS

38°00'

37°45'

119M5' 119 6 30'

FIGURE 5. Bedrock map showing volume percent mafic minerals.
BIO SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

119°45

38°00'

37°45'

119 8 30'

8 KILOMETERS

FIGURE 6. Bedrock map showing specific gravity.
HETCH HETCHY RESERVOIR QUADRANGLE, CALIFORNIA Bll

Quartz Quartz

Modes 

Classification plan

EXPLANATION

0

Alaskite of 

Ten Lakes

Granodiorite 

of Rancheria 

Mountain

x

Granodiorite of 

Mount Hoffman

Granodiorite of 

Double Rock

o

El Capitan Granite 

Quartz diorite of 

South Fork of 

Tuolumne River

Plagioclase Potassium feldspar Plagioclase

Norms of granitic rocks of 

the Yosemite intrusive epoch

Orthoclase

10 35

Alaskite of Ten Lakes

P 10 35

Granodiorite of Rancheria Mountain

10 35

Granodiorite of DouWe Rock

a, granodiorite facies

b, quartz monzonite 

facies

c, quartz-rich granodiorite facies

d, quartz-rich quartz 

monzonite facies

10 35

El Capitan Granite

10 35 

Granodiorite of Mount Hoffman

10 35

Quartz diorite of South Fork of Tuolumne River 

FIGURE 7. Modes and norms of granitic and volcanic rocks. (Figure continued on following page.)
B12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Quartz

Norms of a trachyandesite and 

of granitic rocks of Cathedral 

Range intrusive epoch

EXPLANATION

A

Half Dome Quartz 

Monzonite

O

Sentinel 

Granodiorite

+

Yosemite Creek 

Granodiorite 

of Rose

O

Quartz diorite of 

Mount Gibson

A

Trachyandesite

Plagioclase Orthoclase

10 35

Half Dome Quartz Monzonite

10 35 

Yosemite Creek Granodiorite of Rose

10 35

Sentinel Granodiorite

10

 Quartz diorite of Mount Gibson 

o Quartz diorite of Tamarack Creek

FIGURE 7. Continued.
HETCH HETCHY RESERVOIR QUADRANGLE, CALIFORNIA B13

TABLE 1. Chemical and spectrographic analyses and norms

[Chemical analyses by P. L. D. Elmore, Gillison Chloe, Hezekiah Smith, J. L. Kelsey, and James Glenn. Semiquantitative spectrographic analysis by Chris 

Heropoulos. Results are to be identified with geometric brackets whose boundaries are 1.2, 0.83, 0.66, 0.38, 0.26, 0.18, 0.12, etc., but are reported arbitrarily 

as midpoints of these brackets: 1, 0.7, 0.6, 0.3, 0.2, 0.16, 0.1, etc. The precision of a reported value is approximately plus or minus one bracket at 68 

percent confidence. Looked for but not found: Ag, As, Au, Bi, Cd, Ge, Hf, Ln, Nd, Pd, Pt, Re, Sb, Ta, Te, Th, Tl, U, W, Zn]

Quartz diorite 

of South Fork 

Tuolumne River

K-34-64

El Capitan Granite

K-43-69 K-36-67 K-35-64

Granodiorite of 

Double Rock

K-18-64 H-27-69

Granodiorite of Mount Hoffman

H-47-66 K-51-66 K-i5-66

Chemical analyses (weight percent)

SiCh.........................

ALOs........................

FeO.........................

MgO........................

CaO.........................

NaaO.......................

K2O..........................

H2O+.......................

HaO........................

TiO2.........................

P205.........................

MnO.......................

CO2...... ...................

Sum.............

............... 59.0

................ 17.3

2.2

................ 4.0

............... 3.0

................ 6.2

............... 3.0

............... 2.4

................ 1.0

.............. .23

............... .80

............... .20

............... .09

............... <.05

............... 99

69.8 

14.9 

1.1 

2.1 

.89 

2.7 

3.5 

3.0 

.77 

.17 

.39 

.14 

.04 

<.05

100

70.1 

14.8 

.81 

1.9 

.78 

2.6 

3.7 

3.0 

1.2 

.14 

.35 

.12 

.06 

<.05

100

73.1 

14.3 

1.0 

.92 

.50 

1.4 

3.4 

4.2 

.61 

.12 

.32 

.11 

.03 

<.05

100

71.8 

14.2 

.94 

1.6 

.59 

1.7 

3.0 

4.7 

.67 

.14 

.33 

.08 

.03 

<.05

100

70.3 

14.8 

.70 

2.0 

.78 

2.0 

4.0 

3.8 

1.0 

.10 

.34 

.10 

.07 

<.05

100

72.0 

14.6 

.94 

1.6 

.69 

2.2 

3.2 

3.5 

.62 

.09 

.38 

.04 

.04 

<.05

100

68.2 

15.8 

1.1 

2.1 

.94 

2.7 

3.1 

4.5 

.65 

.13 

.46 

.13 

.06 

<.05

100

72.8 

14.7 

.50 

1.0 

.47 

1.8 

3.7 

4.1 

.50 

.07 

.25 

.06 

.06 

<.05

100

Semiquantitative spectrographic analyses (parts per million)

B

Ba.

Be.............................

Ce.............................

Co............................

Cr.............................

Cu............................

Ga............................

La............................

Nb....... ...................

Mo

NL....... .....................

Pb............................

Sc.............................

Sn............................

Sr.............................

V..............................

Y..............................

Yb............................

Zr........ ....................

............... 700

....... 15

............... 20

............... 30

............... 20

............... 10

............... 20

............... 700

............... 150

9n

2

............... 100

"Too""

............

5 

5 

..._ .....

50

15 

3

300 

30 

10 

1.5 

150

2,000 

............

3 

3

1 

20 

70

20 

5

500 

30 

10 

1 

150

700 

5

2

.7 

20

7

"io" "

5

300 

20 

10 

1.5 

100

700 

5

""2"""

.7 

15

""30"""

7

150 

15 

15 

1 

70

700 

2 

100 

2 

2 

.7 

20 

50 

15

""io"""

7

200 

20 

30 

3 

100

1.000 

............

2 

3 

2 

15 

30

"is """

5

300 

30 

10 

1.5 

70

1,500 

...........

2 

2 

15

"To"""

7

300 

30 

10 

............

600" 

3

............ 

20

16

'"26""" 

5 

15 

150 

10 

30 

.7 

70

CIPW norms (weight percent)

Q..............................

C.......... ....................

or..............................

ab.............................

fs......... ....................

iL..............................

ap.............................

................ 13.87

................ 14.27

............... 25.53

9fi ftl

............... 1.18

rt KO

............... 4.40

............... 3.21

............... 1.53

..._......_... .48

30.31 

1.33

17.82 

29.77 

12.54

..... . 

2.39 

1.60

.74 

.33

29.76 

1.03 

17.81 

31.45 

12.17

............

2.36 

1.18

.67 

.29

33.63 

1.88 

24.82 

28.77 

6.23

1.25 

.39 

1.45

.61 

.26

31.37 

1.28 

27.84 

26.44 

7.93

1.47 

1.68 

1.37

.63 

.19

26.12 

.71 

22.46 

33.85 

9.27

""i'.94" 

2.66 

1.02

.65 

.24

33.66 

1.66 

20.70 

27.11 

10.66

1.72 

1.61 

1.36

.72 

.10

25.11 

1.23 

26.63 

26.27 

12.56

2.34 

2.32 

1.60

.86 

.31

30.69 

1.05 

24.23 

31.31 

8.54

'""i.'i"?

1.12 

.73

.48 

.14
B14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 1. Chemical and spectrographic analyses and norms Continued

Granodiorite of Rancheria Mountain

SiO2..................

ALOs................

FezOs...............

FeO..................

MgO.................

CaO..................

Na2O................

K2O..................

H2O+................

H2O.................

TiO2.................

PaOs.................

MnO.................

CO2...................

Sum......

H-22-69

............ 74.2

............ 14.0

............. .40

............ 1.0

............ .35

............ 1.7

............ 3.1

............. 4.1

............ .54

............. .11

............. .15

............. .04

............ .04

............ <.05

............ 100

H-33-69

69.0 

16.5 

.84 

1.6 

.65 

2.4 

3.7 

3.8 

.78 

.08 

.32 

.13 

.06 

<.05

100

H^34-69

Chemical

76.6 

12.9 

.29 

.55 

.09 

.89 

3.7 

4.3 

.00 

.04 

.07 

.02 

.06 

.03

99.5

D-6 FD-31

Alaskite of Ten Lakes

K-45-67 H-25-69

Quartz diorite Quartz diorite of 

of Gibson Yosemite Creek 

Mountains of Rose

H-ll-69 K-29-66 H-48-69

analyses (weight percent) Continued

74.9 

13.5 

.28 

.84 

.33 

1.5 

3.0 

4.2 

.48 

.18 

.12 

.05 

.03 

<.05

99

Semiquantitative spectrographic

B.......................

Ba.....................

Be.....................

Ce.....................

Co.....................

Cr.....................

Cu.....................

Ga.....................

La.....................

Nb....................

Mo....................

NL....................

Pb.....................

Se.....................

Sn.....................

Sr.....................

V......................

Y

Yb.....................

Zr.....................

Q.......................

c

ab.....................

fs......................

mt.

hm ...

iL......................

ap . _ . ___

............ 1,000

............ 1.5

............. 100

............. 2

7

............ 20

............ 50

............ 30

............. 3

............. 300

............. 10

............ 10

............. 1

............. 70

............ 35.92

............ 1.48

............ 24.29

............. 26.30

............. 8.19

............ .87

1.34

............ .58

. ...... .29

... ........ .10

1,500 

2

............

1.7 

20

15

7

500 

20

1 

150

26.40 

2.25 

22.49 

31.35 

11.07

..... . 

1.83 

1.22

""".61 

.31

1.500

 "" 

1.5 

20

20

300 

10

70

CIPW

36.30 

.56 

25.50 

30.92 

4.45

1.06 

.20

1,500

2

1.7 

20

30

300 

10

100

77.4 

12.2 

.51 

.45 

.16 

.63 

3.66 

4.49 

.00 

.00 

.12 

.02 

.06 

.03

99.7

76.9 

12.7 

.15 

.76 

.09 

.82 

3.4 

4.1 

.58 

.14 

.08 

.05 

.05 

<.05

.100

75.0 

14.4 

.64 

.60 

.06 

.73 

3.1 

4.5 

.71 

.10 

.10 

.00 

.00 

<.05

100

55.6 

17.2 

2.1 

5.8 

4.4

7.7 

3.0 

1.6 

.80 

.18 

1.2 

.13 

.10 

<.05

100

62.0 

16.1 

2.2 

3.4 

2.5 

5.4 

3.4 

2.0 1.7" 

.13 

.87 

.20 

.07 

<.05

100

65.2 

17.3 

1.7 

2.5 

1.8 

4.4 

3.6 

1.7 

.75 

.09 

.63 

.26 

.06 

<.05

100

analyses (parts per million) Continued

1,000 

2

1.5 

20

20

200 

10

70

700 

3

.7 

20

50

100

10 

1 

50

10 

700

2 

15

30

20 

5

70

15

1 

70

20 

500

20 

70 

70 

20

30 

10 

20

700 

150 

15 

2 

70

700

15 

10 

15 

30

7 

15 

15

700 

150 

20 

2 

70

1,500

100 

7 

10 

7 

20 

50

............

20 

10

700 

70 

15 

1 

100

norms (weight percent) Continued

37.50 

1.42 

24.97 

25.54 

7.16

.83 

1.18 

.41

""""23 

.12

37.56 

.12 

25.05 

30.92 

3.14

.21 

.40 

.74 

........ 

39.19 

1.30 

24.27 

28.82 

3.75

.23 

1.24 

.22

.15 

.12

38.01 

3.10 

26.61 

26.25 

3.62

.15 

.24 

.98

.38

7.97 

..... . 

25.43 

28.80

3.60 

10.98 

7.13 

3.05

""'2"28 

.31

19.01

"~rr.~82 

28.78 

22.77 

............

6.23 

3.12 

3.19 

..... _. 

.47

25.35 

2.16 

10.05 

30.47 

20.13

.... ._. 

2.26 

2.47

""T.2"6 

.62
HETCH HETCHY RESERVOIR QUADRANGLE, CALIFORNIA

TABLE 1. Chemical and spectrographic analyses and norms Continued

B15

K-46-64

Sentinel Granodiorite 

H-40-64 K-5-64 K-37-67 K-7-64

Half Dome Quartz 

Monzonite 

H-38-69 H-42-69

Aplite H-41-69

Trachyandesite 

H-9-69

Chemical analyses (weight percent) Continued

61.0 

16.4 

2.1 

3.8 

2.9 

5.4 

3.4 

2.6 

1.0 

.12 

.84 

.21 

.06 

<.05 

100

66.5 

15.6 

1.5 

2.5 

1.7 

4.2 

3.4 

3.0 

.69 

.10 

.63 

.16 

.04 

<.05

100

58.5 

18.0 

2.2 

3.8 

3.0 

6.5 

3.3 

1.8 

.90 

.20 

1.0 

.27 

.09 

<.05

100

67.8 

17.2 

1.6 

1.8 

1.3 

4.2 

3.6 

2.6 

.58 

.13 

.66 

.18 

.05 

<.05

99

Semiquantitative spectrographic

"TOO"""

15 

20 

50 

20

.............

10 

20

700 

150 

15 

2 

100

"fob""

100 

10 

15 

7 

20 

50

"T" 

15

T

700 

70 

10 

.T 

TO

700

15 

30 

15 

20

............

20 

10 

15

1,000 

100 

15 

1.5 

70

1,000 1

7 

5 

5 

20

............

............ 

5

61.1 

1T.5 

2.3 

3.0 

2.1 

5.2 

3.8 

2.2 

1.0 

.16 

.82 

.25 

.07 

<.05

100

70.8 

14.4 

1.2 

1.2 

.87 

2.9 

3.4 

3.7 

.59 

.10 

.28 

.09 

.03 

<.05

100

70.4 

14.5 

1.5 

1.3 

1.0 

2.8 

3.2 

4.1 

.56 

.06 

.36 

.12 

.04 

<.05

100

T6.5 

13.3 

.26 

.40 

.16 

1.4 

3.0 

4.4 

.44 

.05 

.06 

.02 

.00 

<.05

100

55.0 

16.8 

3.2 

4.1 

4.1 

6.5 

3.5 

3.4 

.84 

.46 

.44 

.T5 

.09 

<.05

99

analyses (parts per million) Continued

,000

............

10 

20 

20

5 

...........

1,000 1,000 

70 100 

10 10 

.T 1 

100 150

500

5 

3 

3 

15

............

30 

3

500 

50 

............

50

700

5 

2 

T 

10

............ 

3

500 

50

3 

30

15 

200 

2

........... 

15

............

150 

.............

7

100 

1,500 

3 

150 

20 

150 

100 

20 

TO 

15 

5 

TO 

20 

20

1,000 

200 

20 

1 

200

CIPW norms (weight percent) Continued

14.97

15.39 

28.82 

21.85

1.51 

T.24 

3.97 

3.05

1.60 

.50

23.36

17.72 

28.76 

18.44

.56 

4.23 

2.39 

2.1T

1.20 

.38

13.49

10.68 

28.05 

29.11

""""63 

7.51 

3.69 

3.20

1.91 

.64

25.60 

1.24 

15.11 

29.95 

19.33

""sTs

.97 

2.28

" ""i".~23 

.42

16.00 

.01 

13.07 

32.32 

24.29

5.26 

2.40 

3.35

1.57 

.60

29.52

21.96 

28.90 

13.16

""""29

2.18 

.81 

1.75

.53 

.21

28.68

"24.~24 

2T.09 

13.10 

............

2.49 

.63 

2.18

.68 

.28

38.84 

1.11 

26.00 

25.39 

6.82

.40 

.42 

.38

""""ll 

.05

3.33

20.26 

29.86 

20.25

3.06 

10.30 

4.36 

4.68

.84 

1.T9

TABLE 2. Potassium-argon gases

[Constants used K40 : 76=0.584 X10-10 year-1 , 70=4.72X10-10 year-1 ; isotopic abundance 1.19X1Q-* moles K40 per mole K. 

Radiogenic argon=rAr40 ; total argon=tAr40 . Analysts: Lois Schlocker and R. W. Kistler]

Specimen

D-2..........

H-27........

Rock name

Mount Gibson.

Tamarack Creek.

dated

Hornblende . 

Biotite ...........

Hornblende .

K2O

(weight 

percent)

..... 8.70

..... .725 

..... 9.40

..... .847

rAr40

(moles per g X 10-")

109.77

8.95 

126.82

12.30

rAr«

tAr« 

(percent)

91

73 

92

80

(m.y.)

83.7+1.6

81.9 + 2.0 

89.4 ±1.5

95.9 ±2.2

U.S. GOVERNMENT PRINTING OFFICE: 1974 543 5S1/61