Geochemistry and Petrology of "' '•••-" ? •' -- ' «*, : ,.: ' ; "" 5 ?• •• '- . ••- : t**Slf •• ".: ____

Oligoeene and Miocene M\sh-Flow Tuffs of the 

Southeastern Great Basing Nevada

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STENNIS SPACE CENTER, Mississippi-Bldg. 3101
Geochemistry and Petrology of

Oligocene and Miocene Ash-Flow Tuffs of the

Southeastern Great Basin, Nevada

By Edward A. du Bray

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1559

Compositional characterization and evaluation of 

geochemical zonation in ash-flow tuffs of the 

White River Narrows area

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For sale by U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government

Library of Congress Cataloging-in-Publication Data

du Bray, E. A.

Geochemistry and petrology of Oligocene and Miocene ash-flow tuffs of the 

southeastern Great Basin, Nevada / by Edward A. du Bray.

p. cm.—(U.S. Geological Survey professional paper ; 1559)

Includes bibliographical references.

Supt.ofDocs.no.: I 19.16: 1559

1. Volcanic ash, tuff, etc.—Nevada. 2. Geology, Stratigraphic— 

Oligocene. 3. Geology, Stratigraphic—Miocene. 4. Geochemistry— 

Nevada. 5. Geology—Nevada. I. Title. II. Series. 

QE461.D8 1994

552'.23' 097931—dc20 94-31161

CIP
CONTENTS

Abstract........................................................................................................................... 1

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

Stratigraphy of Ash-Flow Tuffs in the Narrows Area.................................................... 3

Sampling and Analytical Methods ................................................................................. 8

Geochemistry.................................................................................................................. 11

Compositional Characteristics................................................................................ 11

Vertical Zonation.................................................................................................... 29

Discussion....................................................................................................................... 32

Correlation.............................................................................................................. 32

Zonation.................................................................................................................. 34

Concluding Remarks...................................................................................................... 35

References Cited............................................................................................................. 36

FIGURES

1. Index map showing location of White River Narrows area and of ash-flow tuff composition profiles..................... 2

2. Total alkali-silica variation diagram for ash-flow tuffs, White River Narrows area.................................................. 6

3-8. Photographs showing:

3. Outcrops of Lund Formation, Petroglyph Cliff Ignimbrite, Monotony Tuff, and Baldhills Member of the

Isom Formation in cliffs north of White River Narrows..................................................................................... 7

4. Outcrops of continuous section from Baldhills up through Hole-in-the-Wall Members of the

Isom Formation between Lund and Leach Canyon Formations......................................................................... 8

5. Upper part of section between Lund and Leach Canyon Formations................................................................. 9

6. Tuff of Hancock Summit, upper cooling unit of the Shingle Pass Tuff, Hole-in-the-Wall Member of the 

Isom Formation, Leach Canyon Formation, Swett Tuff Member, Bauers Tuff Member, and Pahranagat 

Fonnation..........................................................._ 10

7. Uppermost part of upper cooling unit of the Narrows Member of the Leach Canyon Formation, Swett Tuff

Member, Bauers Tuff Member, and base of Pahranagat Formation................................................................... 11

8. Uppermost part of the upper cooling unit of the Narrows Member of the Leach Canyon Formation, Swett

Tuff Member, Bauers Tuff Member, Pahranagat Formation, and Harmony Hills Tuff...................................... 22

9. Variation diagrams showing abundances of selected major oxides and trace elements in ash-flow tuffs, White

River Narrows area .................................................................................................................................................... 23

10. Trace element-tectonic setting discrimination variation diagrams showing average compositions of ash-flow

tuffs, White River Narrows area ................................................................................................................................ 24

11. Ternary AFM diagram showing compositions of ash-flow tuffs, White River Narrows area................................... 24

12. Variation diagram showing average rubidium and strontium abundances in ash-flow tuffs, White River

Narrows area.............................................................................................................................................................. 24

13. Ternary variation diagram showing average relative proportions of rubidium, barium, and strontium in ash-flow

tuffs, White River Narrows area ................................................................................................................................ 25

14. Chondrite-normalized extended trace-element diagram showing average compositions of ash-flow tuffs,

White River Narrows area.......................................................................................................................................... 25

15. Chondrite-normalized rare earth element diagram showing average compositions of ash-flow tuffs,

White River Narrows area.......................................................................................................................................... 25

16. Diagrams showing stratigraphic compositional variation of ash-flow tuffs, White River Narrows area .................. 26

17. Diagrams showing enrichment-depletion factors calculated from compositions of stratigraphic ally lowest and

highest samples in composition profiles for ash-flow tuffs, White River Narrows area ........................................... 28

in
IV CONTENTS

18. Histogram showing enrichment-depletion abundance behavior of oxides and elements in samples from

composition profiles of the ash-flow tuffs, White River Narrows area...................................................................... 31

19. Histogram showing within-unit enrichment-depletion abundance behavior of oxides and elements in

composition profile sample suites of ash-flow tuffs, White River Narrows area....................................................... 31

20. Variation diagrams showing compositions of samples in the stratigraphic interval between the Baldhills and

Hole-in-the Wall Members of the Isom Formation .................................................................................................... 33

TABLES

1. Age, approximate average thickness, and location of systematically, vertically sampled sections of ash-flow

tuffs in the White River Narrows area........................................................................................................................ 3

2. Summary of petrographic characteristics of ash-flow tuffs in the White River Narrows area................................... 4

3. Chemical composition of samples from composition profiles of middle Tertiary ash-flow tuffs in the

Seaman Range............................................................................................................................................................ 12

4. Chemical compositions of middle Tertiary ash-flow tuffs in the White River Narrows area..................................... 16

5. Average major oxide, CIPW normative, and trace-element compositions of middle Tertiary ash-flow tuffs

in the Seaman Range .................................................................................................................................................. 19

6. Summary of enrichment and depletion relations for ash-flow tuff units exposed in the Seaman Range................... 30
Geochemistry and Petrology of Oligocene and Miocene 

Ash-Flow Tuffs of the Southeastern Great Basin, Nevada

By Edward A. du Bray

ABSTRACT

A composite stratigraphic section in the White River 

Narrows area of southeastern Nevada contains 18 regionally 

distributed middle Tertiary dacite to rhyolite ash-flow tuffs 

erupted from several caldera sources within subductionrelated volcanic fields of the Great Basin in western North 

America. Geochemical data for these tuffs provide an excellent opportunity to study stratigraphic and petrologic relations of voluminous middle Tertiary ash-flow tuffs erupted 

from three major caldera complexes in the southeastern part 

of the Great Basin. Chemical data for each of these tuffs are 

distinctive and provide a significant addition to petrographic, 

stratigraphic, geochronologic, and paleomagnetic data used 

to identify and correlate these units. The compositional 

range defined by these ash-flow tuffs is relatively limited.

Vertical geochemical zonation in source magma reservoirs, as deduced from compositional data from systematically collected stratigraphic sections, is distinct from, though 

generally similar to, that described for some high-silica rhyolite systems, such as the Bishop Tuff. The sense of vertical 

enrichment and depletion for many oxides and elements is 

inconsistent among the various stratigraphic units; in addition, the magnitudes of enrichments and depletions are significantly smaller than those described for other high-silica 

rhyolite systems. Only the abundances of SiO2, rubidium, 

tantalum, and cesium systematically decrease upsection 

within each of the studied ash-flow tuffs, and only the abundances of CaO, cobalt, iron, and strontium systematically 

increase upsection. Variability in the sense and magnitude of 

enrichments and depletions in the ash-flow tuffs in the White 

River Narrows area suggests that no single process is responsible for evolution of these magmas. Crystal fractionation 

involving variable mineral assemblages may be the principal 

process that controlled development of the geochemical 

zonation portrayed by these tuffs.

INTRODUCTION

Middle Tertiary volcanic rocks in the Great Basin are 

generally similar to those in large, well-studied middle

Tertiary volcanic fields, including the San Juan, Marysvale, 

and Mogollon-Datil, in western North America. Knowledge of middle Tertiary volcanic rocks in large parts of the 

Great Basin is relatively incomplete, however, and a number of major stratigraphic and petrogenetic questions 

remain unanswered.

The White River Narrows area, termed an "outflow 

alley" by Best and others (1993) because of remarkably 

complete preservation of Oligocene and Miocene ash-flow 

tuffs in the area, is in the overlap zone between three of the 

largest caldera complexes (Indian Peak, Central Nevada, and 

Caliente) in the southeastern Great Basin and therefore provides an excellent opportunity to study stratigraphic relations and petrologic evolution associated with voluminous 

middle Tertiary magmatism. Geochemical characteristics 

and interpretations presented here for tuffs of the White 

River Narrows area are probably applicable to distributions 

of these tuffs throughout the southeastern Great Basin. Furthermore, because the tuffs exposed in the White River Narrows area represent a major component of magma erupted 

from middle Tertiary sources in this area, their geochemistry 

exemplifies that of middle Tertiary magmatism throughout 

the southeastern Great Basin.

In the Seaman Range (fig. 1), about 180 km north of 

Las Vegas, the White River Narrows area (hereafter 

referred to as the Narrows area) is centrally located within 

the province affected by voluminous middle Tertiary ashflow eruption (Best, Christiansen, and others, 1989). Complete stratigraphic sections of all but the oldest and youngest of 18 middle Tertiary, outflow-fades ash-flow tuffs are 

present in the Narrows area (Hurtubise and du Bray, 1992). 

Age, approximate average thickness, and stratigraphic relations for ash-flow tuffs exposed in the Narrows area are 

summarized in table 1.

The majority of the igneous rocks exposed in the Great 

Basin are ash-flow tuffs (Best, Christiansen, and others, 1989) 

whose origins are related to arc magmatism associated with 

Cenozoic subduction along the western margin of North 

America (Christiansen andLipman, 1972; Lipman and others, 

1972;Lipman, 1980; Johnson, 1991; Ward, 1991). Studies by 

Mackin(1960),Cook(1965),andWilliams(1967)providethe 

earliest stratigraphic and petrographic descriptions of these
OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Figure 1. Index map showing location of the White River Narrows area and locations of ash-flow tuff composition profiles. 

Shaded areas show the distribution of the indicated mountain 

ranges. Unit designations: NL, PC, Lund Formation and Petroglyph Cliff Ignimbrite (southeast and northwest parts of profile, 

respectively); MT, Monotony Tuff; LC, lower and upper cooling 

units of the Leach Canyon Formation (southeast and northwest 

parts of profile, respectively); PF, Pahranagat Formation; HH, 

Harmony Hills Tuff; CS, CB, Swett and Bauers Tuff Members of 

the Condor Canyon Formation (southeast and northwest parts of 

profile, respectively); HT, Hiko Tuff; BH-HW, Baldhills Member 

of the Isom Formation, lower and intermediate cooling units of the 

Shingle Pass Tuff, tuffs of the Golden Gate Range and Hancock 

Summit, upper cooling unit of the Shingle Pass Tuff, and the 

Hole-in-the-Wall Member of the Isom Formation (southeast 

through northwest parts of the profile, respectively).

rocks. During the 1960's,Ekren and others (1971,1977) added 

considerably to the understanding of volcanic rocks in the 

southwestern and south-central parts of the Great Basin. 

Anderson and Rowley (1975) and Rowley and others (1979) 

described stratigraphic and lithologic features of Great Basin 

ash-flow tuffs that extend into southwestern Utah. Best, Christiansen, and others (1989) summarized knowledge concerning 

middle Tertiary volcanic rocks of the Great Basin. The most 

recent syntheses and presentations of new geochronologic, 

petrographic, paleomagnetic, and stratigraphic data for tuffs 

of southeastern Nevada are those of Best and others (1993), 

Rowley and others (in press), and Scott and others (in press).

Geologic mapping (du Bray and Hurtubise, 1994) demonstrates that the ash-flow tuff section in the Narrows area is 

remarkably complete. A composite section of the 18 units, 

compiled from numerous individual sections in the area (fig. 

1), contains no obvious erosional intervals and very minor 

interbedded sedimentary deposits. The majority of the individual sections is in the White River Narrows (fig. 1), an area 

that has been recognized since Cook's (1965) work as containing the most complete section of middle Tertiary ashflow tuffs in the southeastern Great Basin.

The chemical compositions of tuffs in the Narrows area 

are distinctive. Compositional data, especially for trace elements, can be combined with petrographic (Mackin, 1960; 

Williams, 1960, 1967; Cook, 1965), stratigraphic (Best, 

Christiansen, and others, 1989; Rowley and others, in press; 

Scott and others, in press), paleomagnetic (Gromme and others, 1972; Scott and others, in press), and geochronologic 

(Armstrong, 1970; Deino and Best, 1988; Best, Christiansen, 

and others, 1989; Best and others, 1993; Rowley and others, 

in press; Scott and others, in press) data to identify and correlate ash-flow tuffs in the southeastern part of the Great 

Basin where stratigraphic problems are unresolved.

Vertical compositional zonation within each of the tuffs 

in the Narrows area differs from that documented for other 

high-silica rhyolite ash-flow tuffs. The observed zonations 

are discontinuous and variable with regard to whether particular elements are concentrated in their early- versus lateerupted parts; enrichment-depletion factors are smaller than 

those documented for high-silica rhyolite tuffs studied by 

Smith (1979) and Hildreth (1979). The nature and extent of 

these differences may indicate that magma reservoirs represented by tuffs of the Narrows area became compositionally 

zoned by fractionation of distinctive sets and proportions of 

minerals. The evolution of vertical compositional zonation 

must be carefully evaluated. Zonation probably does not 

derive from a unique, universally operative process but 

rather from various processes in different magma reservoirs.

The availability of a large, well-documented body of 

compositional data for the tuffs of the Narrows area enables 

its comparison with data for other volcanic rocks of the Great 

Basin (Cans and others, 1989; Best and Christiansen, 1991; 

Feeley and Grunder, 1991) and with data for other major 

middle Tertiary volcanic fields of southwestern North America. Time-space-composition comparisons of this type may 

help refine interpretations of the plate tectonic processes 

(Johnson, 1991; Ward, 1991) that produced the major, middle Tertiary volcanic fields of southwestern North America.

Acknowledgments.—This study is an outgrowth of a 

mineral resource assessment of the U.S. Bureau of Land 

Management Weepah Spring Wilderness Study Area. I am 

indebted to P.D. Rowley, D.A. Sawyer, W.A. Duffield, and 

M.G. Best whose incisive reviews helped improve the 

focus and enhance interpretive sections in early drafts of 

the manuscript.
STRATIGRAPHY OF ASH-FLOW TUFFS IN THE NARROWS AREA

Table 1. Age, approximate average thickness, and location of systematically, vertically sampled sections of ash-flow tuffs in the White

River Narrows area, Nevada.

[Units are arranged in stratigraphic order; youngest units are at the top of table. Unit designations as used in figures are given in parentheses]

Unit

HikoTuff(HT)

Harmony Hills Tuff (HH)

Pahranagat Formation (PF)

Condor Canyon Formation

Bauers Tuff Member (CB)

Swett Tuff Member (CS)

Narrows Member of the Leach Canyon Formation

Upper cooling unit (LCU)

Lower cooling unit (LCL)

Hole-in-the Wall Member of the Isom Formation (HW)

Shingle Pass Tuff, upper cooling unit (SPU)

Tuff of Hancock Summit (HS)

Tuff of Golden Gate Range (GG)

Shingle Pass Tuff

Intermediate cooling unit (SPI)

Lower cooling unit (SPL)

Baldhills Tuff Member of Isom Formation (BH)

Monotony Tuff (MT)

Petroglyph Cliff Ignimbrite (PC)

Needles Range Group

Lund Formation (NL)

Wah Wah Springs Formation (NW)

Isotopic Thickness 

age (Ma) 1 (meters)

18.6

22±

22.65

22.78

23±

23.8

26.0

?

?

26.4-26.5

26.7

27.0

27.31

27.6±

27.9

-30

15

0-10

15

25

10

140

15

70

45

75

40

45

2

60

10

40

20

Location of composition profile 

Base Too

Latitude

37°49'51"

37°50'25"

37°50'36"

37°50'18"

37°50'17"

37°51'03"

37051'02"

37°45'15"

37°45'13"

37°45'12"

37°45'10"

37°45'09"

37°45'08"

37°45'08"

37°52 50"

37°54 28"

37054 29-

-

Longitude

115°02'14"

115°01'56"

115°01'38"

115°01'48"

115°01'47"

115°01'14"

115°01'13"

115°10'56"

115°10'51"

115°10'48"

115°10'43"

115°10'40"

115°10'37"

115°10'37"

115°00'58"

115°01'05"

115001'02"

--

Latitude

37049.54-

37°50'25"

37°50'37"

37°50'23"

37°50'18"

37°51'08"

37°51'03"

37°45'16"

37°45'15"

37°45'13"

37°45'12"

37°45'10"

37°45'09"

37°45'08"

37°52 54"

37°54 28"

37°54 28"

-

Longitude

115°02'15"

115°01'58"

115°01'40"

115°01'49"

115°01'48"

115001'20"

115°01'14"

115°10'58"

115°10'56"

1150 10'51"

115°10'48"

115°10'43"

115°10'40"

115°10'37"

115°01'ir

115°01'08"

115°01'05"

--

^ee text for sources of ages.

STRATIGRAPHY OF ASH-FLOW 

TUFFS IN THE NARROWS AREA

Middle Tertiary ash-flow eruptions resulted in numerous calderas in the Great Basin; locations, products, and ages 

of these calderas are summarized by Best, Christiansen, and 

others (1989, fig. 7, table 2). These tuffs were derived from 

sources in one of three caldera complexes: the Indian Peak 

caldera complex—Wah Wah Springs and Lund Formations 

and the Baldhills and Hole-in-the-Wall Members of the Isom 

Formation; the Central Nevada caldera complex—Monotony and Shingle Pass Tuffs, tuff of the Golden Gate Range, 

tuff of Hancock Summit, and Pahranagat Formation; and the 

Caliente caldera complex—Leach Canyon and Condor Canyon Formations and Harmony Hills and Hiko Tuffs. The oldest and youngest tuffs of the Narrows area are the ~30-Ma 

Wah Wah Springs Formation (Best and others, 1993) and the 

18.6-Ma Hiko Tuff (Taylor and others, 1989) (table 1). 

Stratigraphic relations and important features of the tuffs of 

the Narrows area, from oldest to youngest, are described following; petrographic attributes are summarized in table 2.

The oldest ash-flow tuffs in the Narrows area are part of 

the Oligocene Needles Range Group (Best and Grant, 1987), 

named for exposures in the Needles Range of western Utah 

and deposited on an undulating surface of Paleozoic

carbonate rocks. The Cottonwood Wash Tuff, Wah Wah 

Springs Formation, and Lund Formation of the Needles 

Range Group have a total volume of at least 6,600 km3 and 

were successively erupted from the nested Indian Peak 

caldera complex (Best and Grant, 1987; Best, Christiansen, 

and Blank, 1989). Small and major amounts, respectively, of 

the ~30-Ma Wah Wah Springs (Best and others, 1993) and 

the 27.9-Ma Lund Formations (Best and Grant, 1987) are 

present in the Narrows area; both tuffs are dacite (fig. 2). The 

Wah Wah Springs, the only tuff in the Great Basin that contains more hornblende than biotite (Best and others, 1993), 

forms limited outcrops along the east flank of the Seaman 

Range; the tuff probably wedges out in the subsurface west 

of these outcrops. The Lund Formation forms massive outcrops throughout the Seaman Range (fig. 3) and is particularly well exposed north of White River Narrows (du Bray 

and Hurtubise, 1994).

The Petroglyph Cliff Ignimbrite (fig. 3) of Cook (1965) 

is a lithic-rich dacite ash-flow tuff (fig. 2). The uppermost 

part of this tuff contains distinctive subangular, black glass 

lapilli (20 cm). The unit, whose source caldera is unknown, 

is about 15m thick. The Petroglyph Cliff Ignimbrite is not 

exposed at Cook's (1965) type section, though it is well 

exposed a few kilometers to the north (du Bray and Hurtubise, 1994); the Baldhills Member of the Isom Formation, 

similar in appearance to the Petroglyph Cliff Ignimbrite, is
Table 2. Summary of petrographic characteristics of ash-flow tuffs in the White River Narrows area, Nevada.

[Based on examination of more than 125 thin sections. Representative crystal abundances are based on quantitative modal analyses of about 40 sections and are confir

remaining samples. Leaders (—), not observed; tr, trace. Crystallinity: a, anhedral; s, subhedral; e, euhedral; where two crystallinities are indicated, the first is dominan

unwelded; incip, incipient; mod, moderate; den, dense. Degree of devitrification: non, nondevitrified; incip, incipient; mod, moderate; com, complete. Additional petr

crystals are broken; (2) plagioclase is albite twinned and zoned; (3) sanidine is carlsbad twinned; (4) magnetite is the predominant opaque oxide phase (weakly altered t

grains contain trace amounts of chromite); (5) biotite is pleochroic from tan to very dark reddish greenish brown; (6) hornblende is pleochroic from yellowish green to o

Total 

Unit crystals 

(percent)

HikoTuff 18

(HT)

Harmony Hills 29

Tuff(HH)

Pahranagat 22

Formation

(PF)

BauersTuff 15

Member

(CB)

Swett Tuff Member 5

(poorly welded top)

(CS)

Narrows Member, 14

upper cooling unit

(LCU)

Narrows Member, 10

lower cooling unit

(LCL)

Hole-in-the- Wall 7

Member (HW)1

Shingle Pass Tuff, 8

upper cooling unit

(SPU)

Plag San Otz Bi Hb Oox Cox Mae

Approximate modal abundance (percent) 

Form of crystals 

Grain size (millimeters)

8

a,s

0.2-1.5

16

s

0.2-3.0

6

s

0.2-2.0

8

s,e

0.2-6.0

4

s,e

0.1-3.0

6

s

0.2-2.0

3

s

0.1-1.2

6

s,e

0.2-3.0

4

s,e

0.5-2.0

3

a

1.5

tr

8

s

0.5-1.5

6

s,e

0.2-2.0

~

4

s

0.2-2.0

4

s

0.2-2.5

tr

s

0.5

3

s,e

0.5^.0

4

a

0.1-2.0

1

a

0.5-1.5

7

s

0.2-3.0

-

~

3

s

0.2-1.5

2

s

0.1-2.0

tr

s

0.5

tr

s,a

0.5

2

s

0.2-1.5

5

s

0.2-2.0

1

s

0.1-0.5

1

s

0.2-1.0

1

s

0.2-2.0

1

s

0.1-2.0

1

s

0.2-2.0

„

1

s

0.5-1.5

1

a,s

0.2-1.0

4

s,a

0.1-0.6

tr

s

0.4

~

tr

s

0.2-1.0

tr

a,s

0.1-1.2

-

tr

s

0.1-0.5

tr

a

0.5

tr

2

a,s

0.4-1.0

tr

s

0.4-0.8

tr

s

0.4

tr

s

0.3

tr

a

0.3

tr

a

0.2

tr tr

s s

0.2-0.8 0.2-0.8

tr

a

0.2

tr

a

0.1-0.5

1

a

0.1-0.5

tr

a

0.1-0.4

tr

a,s

0.5

tr

a,s

0.1-0.4

tr

a

0.3

tr

a

0.3

tr

a,s

0.1-0.4

tr

a

0.1-0.4

Accessory 

minerals

Sphene,

allanite,

zircon

Zircon,

apatite,

allanite

Allanite,

zircon

Allanite,

zircon,

apatite

Zircon

Sphene,

allanite,

zircon

Sphene,

allanite,

zircon

Zircon,

apatite

Allanite,

zircon

Degree of 

welding, 

devitrification

Mod,

incip

Weakmod,

variable

Weak,

mod

Weakden,

com

Weakden,

incip

Weak,

mod

Weak,

mod

Den,

modcorn

Den,

variable

Ma

Abundance dus

of pumice sh

lithic domi

Low,

low

Low,

low

High,

low

Low,

low

Low,

low

Mod,

mod

Low,

low

Mod,

mod

High,

low

Sha

Sha

Sha

Sha

Sha

Du

Sha

Sha

Sha
Tuff of Hancock 24

Summit (HS)

Tuff of the 31

Golden Gate

Range (GG)

Shingle Pass Tuff, 16

intermediate cooling

unit (SPI)

Shingle Pass Tuff, 15

lower cooling unit

(SPL)

Baldhills Tuff 16

Member (BH)2

Monotony 22

Tuff(MT)

Petroglyph Cliff 5

Ignimbrite (PC)3

Lund 29

Formation

(NL)

WahWah 41

Springs Formation

(NW)

9

a,s

0.2-2

6

s,e

0.2-2.0

5

a,s

0.4-2.0

5

a,s

0.5-3.0

13

s

0.4-5.0

10

a,s

0.2-1.5

4

s,a

0.1-1.0

16

s

0.2-2.5

25

s

0.2-0.8

7

s

00.2-1.6

13

s,e

0.4-2.0

9

a,s

1.0-3.0

8

s

0.5-2.5

—

4

s

0.8

..

2

s

0.2-2.0

-

5

s

0.2-3.0

11

s,e

0.2-2.0

2

s

0.2-1.2

1

a,s

0.3-2.0

—

6

a

0.2-1.5

tr

a,s

0.2-1.0

5

s,e

0.2-3.0

2

s

0.2-1.0

2

s

0.4-1.5

1

s

0.3-0.6

--

—

—

2

s

0.2-0.5

tr

s

0.2-0.5

4

s

0.1-2.5

4

s

0.5-3.0

1 tr

s s

0.2-2.5 0.5

tr

s,a

0.1-0.8

tr

s

0.5

tr

s

0.5

tr tr

s a,s

0.1-0.5 0.2-0.5

tr

a

0.2

tr tr

a,s a,s

0.1-1.0 0.4

2

a,s

0.1-1.5

9

a,s

0.1-2.0

-

..

1

s

0.5-1.5

—

2

a,s

0.2-0.5

tr

a

0.2

1

a,s

0.4

-

tr

s

0.4-1.5

tr

s

0.2

1

a

0.1-0.4

tr

a

0.1

tr

a

0.1-0.4

1

a,s

0.2

tr

a

0.1

tr

a,s

0.1-0.5

tr

a

0.1-0.4

1

a

0.1-0.3

Allanite,

zircon

Zircon,

allanite

Zircon,

allanite

Zircon,,

allanite,

fayalite

Allanite,

zircon,

apatite

Zircon,

allanite,

apatite

_

Sphene,

allanite,

zircon,

apatite

Zircon,

apatite

Mod,

com

Modden,

weak-mod

Den,

modcorn

Den,

com

Den,

weakmod

Incip,

incip

Den,

incip

Mod,

incipmod

Mod,

weak

Low,

low

Low,

low

Mod,

low

High,

low

High,

low

High,

high

High,

high

High,

low

Mod,

low

D

Sh

Sh

Sh

Sh

D

D

D

D

Contains glomerocrysts of plagioclase, augite, and opaque oxides. 

2Contains glomerocrysts of plagioclase, magnetite, and augite. 

3Upper part contains distinctive, flattened, black glass pumice lapilli.
OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

65 69 73 77 

Si0 2 , IN WEIGHT PERCENT

B

65 69 73 77 

Si0 2 , IN WEIGHT PERCENT

Figure 2. Total alkali-silica variation diagram for ash-flow tuffs 

in the White River Narrows area. International Union of Geological 

Sciences classification grid (Le Bas and others, 1986) is also shown. 

Unit designations identify symbols used in all subsequent figures: 

NW, Wah Wah Springs Formation; NL, Lund Formation; PC, Petroglyph Cliff Ignimbrite; MT, Monotony Tuff; BH, Baldhills Member 

of the Isom Formation; SPL and SPI, lower and intermediate cooling 

units, respectively, of the Shingle Pass Tuff; GG, tuff of the Golden 

Gate Range; HS, tuff of Hancock Summit; SPU, upper cooling unit 

of the Shingle Pass Tuff; HW, Hole-in-the-Wall Member of the Isom 

Formation; LCL and LCU, lower and upper cooling units of the 

Leach Canyon Formation, respectively; CS and CB, Swett Tuff and 

Bauers Tuff Members of the Condor Canyon Formation, respectively; PF, Pahranagat Formation; HH, Harmony Hills Tuff; HT, Hiko 

Tuff. A, Averages (from table 5) of compositions for ash-flow tuffs 

in the Narrows area, Nevada. B, Composition ranges (from tables 3 

and 4) for ash-flow tuffs exposed in the Narrows area.

instead exposed at the designated type section. The phenocrysts, composition, and dense welding of the Petroglyph 

Cliff Ignimbrite are similar to those of Isom-compositionaltype tuffs of Best, Christiansen, and others (1989). Although 

the age of the Petroglyph Cliff has not been determined, its 

eruption is bracketed between 27.9 and 27.31 Ma, the ages 

of the underlying Lund Formation and overlying Monotony 

Tuff, respectively.

The Monotony Tuff is a pumiceous, dacite to rhyolite 

ash-flow tuff (fig. 2, tables 2, 3) that forms recessive-weathering outcrops (fig. 3). In the Narrows area, the Monotony 

Tuff is exposed in a north-trending belt several kilometers 

wide that extends from about 5 km south of White River Narrows to about 10 km south of Black Cliff. Best, Christiansen, 

and others (1989) reported an 40Ar/39Ar age of 27.3 Ma for 

the Monotony. In most places, the Monotony probably is 

composed of a single, thick ash-flow cooling unit. Ekren and 

others (1971) suggested that the Monotony was derived from 

a source in the southern Pancake Range, whereas Best, Christiansen, and others (1989) and Best and others (1993) suggested a source within the Central Nevada caldera complex.

Rocks above the Needles Range Group and the Monotony Tuff and below the Leach Canyon Formation were 

termed the Pahrock sequence by Cook (1965). In the Narrows area, seven lithologically similar ash-flow tuffs crop 

out in this interval (figs. 4-6). These units, informally 

described as units 1-7, from oldest to youngest, of the rhyolite tuffs of the Seaman Range (Hurtubise and du Bray, 1992) 

are correlated with more widely distributed ash-flow tuffs. 

Deposition and preservation of all tuffs in this interval, initially identified on the basis of compositional data presented 

herein, are rare; a complete section is present about 1.5 km 

north of Fossil Peak (figs. 1,4,5). The section exposed in the 

Narrows area is anomalously thin and includes only a few of 

the ash-flow tuffs known to be in this interval.

In the northern cliffs of White River Narrows the 

Monotony Tuff is overlain by the Baldhills Member of the 

Isom Formation. This erosion-resistant tuff is a trachydacitic, 

1-2-m-thick black vitrophyre (fig. 2) erupted 27.0 Ma from 

a probable source in the Indian Peak caldera complex (Best 

and others, 1993). The Baldhills, another Isom-compositional type tuff (Best, Christiansen, and others, 1989), may 

also be correlative with the 27.4-Ma tuff of Hamilton Spring 

(Taylor and others, 1989). Stratigraphically above the Bald 

Hills are six rhyolite ash-flow tuffs (fig. 2) that form both 

massive bouldery outcrops and subordinate recessive intervals. Petrographic and compositional data suggest that the 

first two of these tuffs are the lower and intermediate cooling 

units of the Shingle Pass Tuff, which Sargent and Houser 

(1970) suggest was erupted from the Quinn Canyon caldera; 

Best and others (1993) reported ages of 26.7 Ma and 

26.4-26.5 Ma, respectively, for these tuffs. M.G. Best (oral 

commun., 1989) suggested that the next three tuffs in this 

ascending stratigraphic sequence are correlative with the tuff 

of the Golden Gate Range, with the tuff of Hancock Summit
STRATIGRAPHY OF ASH-FLOW TUFFS IN THE NARROWS AREA

Figure 3. Outcrops of the Lund Formation (NL), Petroglyph Cliff Ignimbrite (PC), Monotony Tuff (MT), and the Baldhills 

Member (BH) of the Isom Formation in cliffs north of White River Narrows. View to the west.

(Best, Christiansen, and others, 1989), whose inferred source 

is an unnamed caldera 85 km west-northwest of Caliente, 

Nev., and with the 26.0-Ma upper cooling unit of the Shingle 

Pass Tuff (Best and others, 1993), respectively. The youngest 

of the tuffs beneath the Leach Canyon Formation is another 

Isom-compositional-type tuff (Best, Christiansen, and others, 1989) and is probably correlative with the Hole-in-theWall Member of the Isom Formation (Best and others, 1993).

The type locality of the 23.8-Ma Leach Canyon Formation (Best and others, 1993), the next youngest tuff in the 

Narrows area, is at Leach Canyon in Utah (Cook, 1965; 

Anderson and Rowley, 1975). Cook (1965) reported a thickness of at least 137 m at White River Narrows (figs. 6-8). 

Williams (1967) suggested the Caliente caldera complex as 

a source for the Leach Canyon, whereas Best, Christiansen, 

and others (1989) suggested an unnamed caldera northeast of 

the complex. The Leach Canyon Formation is widespread in 

the southeast part of the Narrows area, where it forms prominent cliffs, many of which are columnar jointed. Williams 

(1967) defined two members of the Leach Canyon, the Narrows Tuff Member and the overlying Table Butte Tuff Member. Only the Narrows Member is present in the White River 

Narrows area, and it is composed of upper, hornblende-bearing and lower, hornblende-free rhyolite (fig. 2) ash-flow tuff 

cooling units. Chemical compositions of the two ash-flow 

units, described following, are distinct.

The Condor Canyon Formation, which overlies the 

Leach Canyon Formation, was named by Cook (1965); it 

consists of the lower 9-m-thick Swett Tuff Member and the 

upper 32-m-thick Bauers Tuff Member (figs. 6-8). Both 

tuffs are composed of rhyolite ash-flow tuff (fig. 2) and were 

probably erupted from the Caliente caldera complex (Williams, 1967; Rowley and Siders, 1988). Armstrong (1970) 

reported K-Ar ages of 23.9 Ma and 22.1 Ma for the Swett 

and Bauers, respectively. Best, Christiansen, and others 

(1989) reported an 40Ar/39Ar age of 22.78 Ma for the Bauers 

Tuff Member.

The basal part of the Swett Tuff Member is a palebrown and medium-gray vitrophyre as thick as 1.5 m overlain by a thin interval of densely welded pale-red tuff (0.5 m) 

that grades upward into an almost aphyric, poorly welded, 

pale-red tuff (2 m) that in turn is overlain by about 2 m of 

poorly welded pinkish-gray tuff (fig. 7). The Bauers Tuff 

Member includes a variably devitrified black vitrophyre several meters thick. Above its base is about 20 m of densely 

welded pale-red tuff (fig. 7). The uppermost part of the 

Bauers is characterized by densely welded tuff that weathers 

to form resistant slabs.

In the Narrows area (fig. 8), the Pahranagat Formation 

of Scott and others (in press) is exposed discontinuously 

above the Bauers Tuff Member (Condor Canyon Formation); the rhyolite tuff (fig. 2) is less than 15 m thick.
OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Figure 4. Outcrops of the continuous section from Baldhills up through the Hole-in-the-Wall Members (BH-HW) of the 

Isom Formation between the Lund Formation (NL) and the Leach Canyon Formation (LC). View to the west. This section, 

1.5 km north of Fossil Peak, is the only complete section in this stratigraphic interval known in the White River Narrows 

area. Arrow indicates the position, on the leading edge of a backsloping dip slope, from which photograph shown in figure 

5 was taken. The Baldhills Member of the Isom Formation and the lower and intermediate cooling units of the Shingle Pass 

Tuff are exposed between the top of the Lund and the base of the backsloping dip slope.

Williams (1967) reported that the thickness of the Pahranagat Formation, whose type section is in the Pahranagat Valley in southeastern Nevada, ranges from 0 to 35 m and 

averages 15 m. As a consequence of weak welding and induration, the rhyolite tuff weathers to recessive outcrops. Ekren 

and others (1977) suggested the Kawich or Cactus Ranges as 

likely source areas for the tuff, whereas Best, Christiansen, 

and others (1989) suggested a source in the Central Nevada 

caldera complex that they refer to as the Kawich caldera. 

Deino and Best (1988) reported an 40Ar/39Ar age of 22.65 

Ma for the tuff and suggested that it is correlative with all or 

part of the ash-flow tuffs known elsewhere as the tuff of 

White Blotch Spring (Ekren and others, 1971) and the granite-weathering tuff (Snyder and others, 1972).

The Harmony Hills Tuff, which overlies the Pahranagat 

Formation, is composed of dacite (fig. 2); its type locality is 

in the Harmony Mountains of Utah (Mackin, 1960). Cook 

(1965) recorded a thickness of 46 m in the White River Narrows (fig. 8). Blank (1959) suggested that the tuff was 

erupted from the Bull Valley center in southwestern Utah, 

whereas Best, Christiansen, and others (1989) suggested a 

source in the Caliente cauldron complex. Ages determined 

for the Harmony Hills Tuff are highly variable, but the ages 

of enclosing units constrain eruption of the tuff to between

22.5 and 22.0 Ma (Rowley and others, 1989); Best and others 

(1993) suggested an age of 22.2±Ma. Outcrops of the Harmony Hills Tuff in the Narrows area are limited; thin and discontinuous exposures weather to form recessive outcrops.

The youngest ash-flow tuff exposed in the Narrows area 

is the Hiko Tuff. The Hiko type locality is on the east side of 

the Hiko Range in southern Nevada (Dolgoff, 1963). In the 

Narrows area, only the basal 15 m of the Hiko Tuff is exposed. 

The rhyolite tuff (fig. 2) weathers to prominent low cliffs covered by a distinctive moderate-reddish-brown patina. Ekren 

and others (1977) suggested that the Hiko Tuff was erupted 

from the Caliente caldera complex, and Rowley and Siders 

(1988) confirmed this interpretation. Taylor and others (1989) 

reported an 40Ar/39Ar age of 18.6 Ma for the Hiko Tuff.

SAMPLING AND ANALYTICAL 

METHODS

Numerous samples of each ash-flow tuff unit were collected and analyzed in order to establish compositional 

ranges. This procedure is especially important for ash-flow 

tuffs, many of which are derived from zoned magma reservoirs (Hildreth, 1979, 1981). Establishing the full range of 

compositional zonation within each of the tuff units of the
SAMPLING AND ANALYTICAL METHODS

-£-^r f,*f •

•V*"T'*"t w'"".Jt~ '• f * ' i-i. * «•< »?"*•' ^'•"--•^^-^-V^n.-; ^"**'k »• * r^ J..». 

:-•«* -.-^.V. -*etf^-.^ ^-i*^--.^

'*• -—1

Figure 5. Upper part of the section between the Lund Formation and the Leach Canyon Formation (LC); this part of the 

section includes the tuff of the Golden Gate Range, the tuff of Hancock Summit, the upper cooling unit of the Shingle Pass 

Tuff, and the Hole-in-the-Wall Member of the Isom Formation (GG-HW). View to the west from point shown in figure 4.

southeastern Great Basin is essential if composition is to be 

employed as a tool for stratigraphic correlation. Compositional data for samples collected without regard to vertical 

position are unlikely to depict a full composition range 

because the stratigraphically lowest and highest parts of a 

unit may be overlooked in random sampling. Complete, 

unfaulted sections (table 1), hereafter referred to as compositional profiles, of 14 of the 18 ash-flow tuff stratigraphic 

units were identified; exposed sections of the other four 

units, the Baldhills and Hole-in-the-Wall Members of the 

Isom Formation, the tuff of Hancock Summit, and the Wah 

Wah Springs Formation, were too thin or incompletely 

exposed for meaningful vertical sampling.

Whole-rock samples were collected at 216 sites. Of 

these samples, only nine have anomalous (unrepresentative 

of the sampled ash-flow tuff unit) compositions. These nine 

samples are excluded from further consideration; their compositions may reflect alteration or weathering, incorporation 

of unrecognized xenolithic material, flow sorting during ashflow emplacement, or glass shard elutriation, or they may 

represent previously unrecognized local units. Samples were 

coarse crushed at the outcrop and all obvious xenolithic 

material removed. Of the 216 samples, 44 were collected in 

order to document vertical compositional zonation within 

the tuffs of the Narrows area. Two to five samples, depending on unit thickness, were collected at approximately

evenly spaced sites between the base and top of each profile. 

Abundances for an extensive set (described following) of 

trace elements and for the major oxides were obtained for all 

of these samples. The remaining 163 samples, collected 

throughout the Seaman Range and without reference to 

height in section, provide representative areal coverage; 

compositional data for these samples allow comparison of 

large-geographic-area compositional variation with the 

small-area variation identified in the compositional profile 

of each of the Narrows area tuffs. Abundances of a restricted 

set (described following) of trace elements were determined 

for all 163 of these samples, and abundances for the extensive set of trace elements and for the major oxides were 

determined for a representative subset of these samples.

Recent compositional studies of ash-flow tuffs (Fridrich 

and Mahood, 1987; Boden, 1989) have relied on analysis of 

cognate pumice inclusions because these are considered to 

represent quenched magma. Because most of the middle Tertiary tuffs of the southeastern Great Basin are indurated and 

moderately to densely welded (pumices are flattened to the 

extent that they are inseparable from enclosing tuff matrix), 

it was not possible to collect pumice fragments for this compositional study. Lipman (1965) demonstrated that the compositions of middle Tertiary ash-flow tuff vitrophyre 

(including pumice) are, in some cases, considerably modified 

during postmagmatic processes, including devitrification;
10 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Figure 6. Tuff of Hancock Summit (HS), upper cooling unit of the Shingle Pass Tuff (SPU), Hole-in-the-Wall Member 

of the Isom Formation (HW), Leach Canyon Formation (LC), Swett Tuff Member of the Condor Canyon Formation (CS), 

Bauers Tuff Member of the Condor Canyon Formation (CB), and Pahranagat Formation (PF). View to the west. Section is 

on the west side of the northern White River Narrows. Note multiple flow units within the compound cooling unit of the 

Leach Canyon Formation; prominent slope-forming interval about one-fourth of the Leach Canyon Formation thickness up 

from its base marks the break between the lower and upper cooling units of the Narrows Member.

devitrified pumice blocks such as those contained in the tuffs 

of the Narrows area may be of questionable utility in compositional studies.

Potential modifications, resulting from glass shard elutriation and flow sorting during ash-flow emplacement, of 

whole-rock compositions determined for tuffs of the 

Narrows area from magma compositions have not been 

established; however, the coherence of the Narrows area 

compositional data and their moderately systematic variation 

among profile samples suggest that data presented here are 

generally representative of magma compositions and zonation within each source reservoir. In addition, the effects of 

sectoral compositional variation, as indicated by compositional overlap between samples from the profiles and those 

collected throughout the Seaman Range, suggest that sectoral compositional variation is minor. In order to verify that 

whole-rock ash-flow tuff samples are representative of 

magma compositions, a comparative study of pumice samples separated from one of the least welded and indurated 

tuffs of the Narrows area, such as the Pahranagat Formation, 

could be conducted. To further evaluate the potential effects 

of sectoral compositional variation, samples of the Narrows

area tuffs from throughout their southeastern Great Basin 

distributions could be analyzed.

All chemical abundances were determined in analytical 

laboratories of the U.S. Geological Survey in Denver, Colorado. Major oxide abundances were determined by X-ray 

fluorescence techniques (Taggart and others, 1987) (analysts, J.E. Taggart, A.J. Bartel, D.F. Siems, B.C. Robb, and 

K. Stewart). FeO to FeO*(total iron as FeO) ratios were 

adjusted to 0.85, and major oxide abundances were recalculated to 100 percent volatile free. Energy-dispersive X-ray 

fluorescence spectroscopy, using 109Cd and 241 Am radioisotope excitation sources (Elsass and du Bray, 1982), was used 

to determine abundances of a restricted set (Rb, Sr, Y, Zr, 

Nb, and Ba) of trace elements (analyst, E.A. du Bray); the 

precision and accuracy of these data are discussed by Sawyer 

and Sargent (1989) and Yager and Quick (1992). The abundances of an extensive set of trace elements (Co, Ni, Cr, Cs, 

Hf, Sb, Ta, Th, U, Zn, Sc, La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, 

Yb, and Lu) were determined by instrumental neutron activation analysis (Baedecker and McKown, 1987) (analysts, 

R.J. Knight, J.R. Budahn, and R.B. Vaughn). Analytical precision is graphically portrayed in figure 16.
GEOCHEMISTRY 11

p. *••

f^ ' 4

Figure 7. Uppermost part of the upper cooling unit of the Narrows Member (LCU) of the Leach Canyon Formation, the 

Swett Tuff Member of the Condor Canyon Formation (CS), the Bauers Tuff Member of the Condor Canyon Formation (CB), 

and the base of Pahranagat Formation (PF). View to the northeast. Section is on the east side of northern White River Narrows.

GEOCHEMISTRY 

COMPOSITIONAL CHARACTERISTICS

The International Union of Geological Sciences classification of volcanic rocks (Le Bas and others, 1986) was 

applied to the compositions of the tuffs of the Narrows area 

(tables 3-5). On the basis of the total alkalis versus silica 

criterion of Irvine and Baragar (1971), all but one of the ashflow tuff units is subalkaline; all are members of the highpotassium calc-alkaline series defined by Ewart (1982). The 

Baldhills Member of the Isom Formation is transitionally 

alkaline and is trachydacite, whereas the other tuffs are rhyolite and dacite. Ash-flow tuffs exposed in the Narrows area 

are metaluminous to weakly peraluminous, and about half of 

them are corundum normative (table 5); these features may 

reflect minor, posteraptive alkali loss relative to alumina and 

are probably not primary magmatic characteristics.

As is typical for most calc-alkaline rocks, abundances 

of A12O3, total iron, MgO, CaO, P2O5 , TiO2, and Sr decrease 

continuously with increasing SiO2 in tuffs of the Narrows 

area, whereas abundances of Na2O, MnO, and Zr show no 

clear relationship with SiO2, and abundances of K2O and Rb 

increase with increasing SiO2 (fig. 9). Most of these variation patterns are linear or almost so. Compositional variation 

patterns portrayed by tuffs of the Narrows area are similar to 

those identified for calc-alkaline rocks of the East-Central

Nevada volcanic field (Cans and others, 1989; Feeley and 

Grunder, 1991) and Indian Peak caldera complex (Best, 

Christiansen, and Blank, 1989; Best and Christiansen, 1991).

Best, Christiansen, and others (1989) defined two compositional types of ash-flow tuff, the Monotony and Isom, in 

the Great Basin. In the Narrows area the Monotony type is 

represented by the Wan Wan Springs and Lund Formations 

and by the Monotony Tuff itself, whereas the Isom type is represented by the Petroglyph Cliff Ignimbrite and by the Baldhills and Hole-in-the-Wall Tuff Members of the Isom 

Formation. Monotony-type tuffs of the Narrows area are 

crystal-rich, voluminous, relatively featureless dacite, 

whereas Isom-type tuffs are crystal-poor plagioclasepyroxene phyric trachydacite tuff characterized by elevated 

abundances of TiO2, K2O, Zr, and the middle to heavy rare 

earth elements relative to rocks of similar silica contents.

As suggested by Best, Christiansen, and others (1989), 

continued study of Great Basin tuffs could lead to the identification of additional compositional types. Classification 

of tuffs in the Narrows area using definitions of the Monotony and Isom types leaves fully two-thirds of these tuffs 

unclassified. These tuffs, most of those erupted from the 

Caliente and Central Nevada caldera complexes, would 

seem to belong to a third, and perhaps most common, compositional type. These tuffs are composed of rhyolite, are 

individually distinctive (based on phenocryst proportions,
12 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Table 3. Chemical composition of samples from composition profiles of middle Tertiary ash-flow tuffs in the Seaman Range,

Nevada.

[Formations are arranged in stratigraphic order, from oldest to youngest. Within each formation, samples are also sequentially arranged from base to

top. FeO/FeO* (total iron as FeO) is adjusted to 0.85. Major oxide analyses are normalized to 100 percent, volatile free. Totalj, original analytical

(pre-normalization) total, with total iron as Fe2O3. LOI, loss on ignition; bdl, below detection limit]

Lund Formation

Sample No. 201454 201455 201456

Petroelvoh Cliff lenimbrite

201457 201458 201459 201460 201719 201720

Monotonv Tuff

201721 201722 201723

Major oxide compositions (weight percent)

Si02

A1203

Fe203

FeO

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

Totalj

LOI

69.26

15.84

0.49

2.49

0.86

3.50

2.60

4.24

0.52

0.17

0.03

99.93

3.07

69.18

15.57

0.57

2.91

0.97

3.26

2.54

4.30

0.52

0.15

0.03

99.19

3.19

64.46

16.43

0.83

4.24

2.00

4.96

2.78

3.31

0.70

0.21

0.07

99.48

3.47

68.30 69.07

14.76 15.50

0.67 0.62

3.43 3.18

1.09 0.86

4.13 2.43

2.51 3.08

4.26 4.21

0.55 0.81

0.23 0.20

0.06 0.03

99.51 99.50

2.95 3.02

65.32

15.87

0.77

3.95

1.47

4.61

3.19

3.58

0.87

0.27

0.09

99.92

1.82

63.72

16.55

0.81

4.11

1.94

5.51

3.01

3.06

0.91

0.30

0.07

99.66

2.54

69.84

15.63

0.49

2.50

1.49

3.50

2.46

3.61

0.36

0.10

0.04

99.60

5.26

69.83

15.34

0.49

2.52

1.35

3.66

2.53

3.78

0.39

0.08

0.03

99.52

3.44

70.63

15.28

0.45

2.31

1.18

3.31

2.50

3.88

0.33

0.07

0.04

99.41

3.60

71.57

15.29

0.36

1.82

0.90

3.13

2.50

4.06

0.26

0.08

0.03

99.50

3.17

71.35

15.25

0.40

2.05

1.15

2.89

2.35

4.14

0.29

0.07

0.05

99.65

3.75

Trace element compositions (parts per million)

Rb

Sr

Y

Zr

Nb

Ba

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

176

458

17

213

17

914

4.81

4.70

3.54

15.4

5.83

0.221

1.46

20.8

4.20

54.4

5.67

61.4

123

43.8

7.16

1.32

5.47

0.655

0.263

1.56

0.225

167

452

21

211

16

934

5.77

8.30

2.74

14.0

5.71

0.230

1.44

20.5

4.08

61.1

6.00

56.2

109

42.6

7.37

1.36

5.25

0.641

0.276

1.59

0.228

143

606

18

221

14

111

10.5

bdl

16.0

11.5

6.28

0.281

1.27

18.6

4.09

69.6

13.0

55.4

115

47.5

8.00

1.58

5.58

0.737

0.367

2.08

0.300

132 126

484 371

17 38

196 327

12 18

912 1,007

10.6 3.38

12.1 11.0

10.7 3.29

4.32 3.20

5.79 8.06

0.357 0.437

1.20 1.46

19.5 17.1

3.13 4.15

57.3 50.7

10.1 12.3

52.7 58.3

109 115

41.0 51.4

6.78 9.36

1.31 1.76

5.66 7.46

0.659 1.040

0.307 0.569

1.86 3.59

0.270 0.510

112

472

27

287

16

930

7.53

11.0

6.87

2.89

6.95

0.321

1.24

14.8

3.79

81.6

13.7

49.2

99.6

42.5

7.98

1.55

6.08

0.884

0.463

2.89

0.412

77

528

35

292

17

888

6.76

14.1

5.31

2.15

7.06

0.374

1.25

14.7

3.77

66.6

13.7

50.6

105

45.3

8.12

1.61

6.09

0.894

0.478

2.94

0.408

130

419

15

131

12

1,182

4.72

7.85

4.85

15.0

3.92

0.166

0.878

12.3

3.50

48.7

7.05

40.7

82.5

32.6

5.34

1.17

3.91

0.474

0.245

1.52

0.213

122

405

17

139

11

1,207

4.57

bdl

5.03

7.59

4.19

0.163

0.837

12.3

3.30

50.7

7.18

44.9

84.3

33.8

5.24

1.20

4.09

0.455

0.233

1.42

0.216

124

352

20

136

7

1,309

4.70

bdl

3.67

4.27

3.96

0.169

0.868

13.4

3.30

50.7

6.43

46.6

91.1

35.0

5.49

1.24

4.26

0.454

0.238

1.41

0.202

128

365

21

126

6

1,325

3.03

10.0

4.89

4.49

3.73

0.119

0.846

15.0

3.47

41.2

5.33

52.1

105

40.5

6.03

1.24

3.84

0.474

0.229

1.39

0.211

134

347

25

140

13

1,276

3.72

bdl

5.57

5.85

3.89

0.211

1.16

14.3

4.35

52.9

5.77

48.1

90.7

36.1

6.01

1.17

3.98

0.552

0.301

1.86

0.265
GEOCHEMISTRY

Table 3. Chemical composition of samples from composition profiles of middle Tertiary ash-flow tuffs in the Seaman 

Range, Nevada—Continued.

13

Shingle Pass Tuff

Intermediate

Lower cooling unit

Sample No. 201731 201730

cooling unit

201729 201728

Tuff of the

Golden

Gate Range

201727 201447

Shingle Pass Tuff, uooer cooling unit

201725 201724 201710 201711 201712

Major oxide compositions (weight percent)

SiO2

A1203

Fe2O3

FeO

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

Totali

LOI

75.04

13.25

0.27

1.39

0.18

1.00

3.09

5.63

0.14

bdl

bdl

99.19

0.96

74.67

13.61

0.29

1.47

0.33

0.99

2.89

5.61

0.14

bdl

bdl

98.92

1.80

74.66

13.48

0.32

1.62

0.28

1.01

2.99

5.44

0.18

bdl

0.02

99.23

1.14

73.27

13.58

0.33

1.71

0.47

1.86

3.00

5.45

0.21

0.06

0.04

99.16

1.80

77.63

12.15

0.19

0.98

0.31

0.95

2.63

5.08

0.08

bdl

bdl

99.12

1.11

76.27

12.83

0.22

1.12

0.26

1.19

2.60

5.35

0.15

bdl

bdl

99.23

0.91

75.24

13.27

0.21

1.08

0.38

1.10

2.92

5.61

0.15

bdl

0.03

99.10

1.03

73.98

13.24

0.23

1.18

0.36

2.31

3.03

5.47

0.16

bdl

0.04

99.35

1.76

73.28

14.55

0.24

1.24

0.93

1.92

2.42

5.18

0.18

bdl

0.06

99.57

5.97

74.50

13.63

0.23

1.19

0.34

1.34

3.09

5.44

0.18

bdl

0.05

99.12

2.89

74.14

13.89

0.25

1.27

0.50

1.49

2.74

5.50

0.18

bdl

0.04

99.44

3.54

Trace element compositions (parts per million)

Rb

Sr

Y

Zr

Nb

Ba

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

215

156

34

197

17

1,023

0.412

bdl

1.30

7.55

6.76

1.08

1.69

32.3

7.08

47.4

5.57

69.9

127

50.2

8.15

1.18

6.09

0.842

0.494

2.93

0.425

223

163

31

211

17

1,212

0.532

10.4

1.67

6.38

7.26

1.00

1.69

33.9

6.22

52.8

5.89

75.4

153

55.6

8.84

1.39

bdl

0.860

bdl

3.04

0.434

202

216

33

216

20

1,501

0.945

bdl

bdl

5.36

7.55

1.07

1.70

33.4

6.63

45.5

6.18

82.8

145

58.1

9.33

1.28

7.07

0.923

0.506

3.11

0.450

194

208

33

223

15

1,467

1.93

8.72

4.53

5.84

6.80

0.629

1.44

26.9

4.92

38.7

5.51

63.5

124

47.0

7.36

1.44

5.84

0.796

0.454

2.76

0.395

196

101

30

91

16

348

0.608

5.60

1.77

4.38

3.58

0.444

1.31

22.7

4.43

29.5

2.17

28.1

53.7

27.0

5.68

0.616

4.64

0.658

bdl

2.32

0.323

157

213

17

143

9

1,213

1.05

bdl

0.530

3.35

4.63

0.312

0.941

25.0

2.90

29.9

2.34

62.4

114

45.8

6.74

1.17

4.24

0.574

0.323

1.92

0.283

202

201

26

152

17

900

1.05

5.60

2.49

6.16

5.24

0.604

1.61

28.5

5.92

36.1

3.07

66.8

124

45.1

6.76

0.884

5.82

0.636

bdl

2.41

0.345

202

220

28

162

17

954

1.31

5.49

2.57

5.79

5.05

0.431

1.52

27.1

4.67

34.1

3.20

62.2

119

42.5

6.29

0.878

5.45

0.615

bdl

2.40

0.350

183

215

29

156

16

879

1.08

7.30

1.33

6.49

5.26

0.984

1.60

28.6

6.28

38.5

3.09

66.3

130

42.8

6.95

0.865

5.76

0.646

0.415

2.62

0.381

192

213

26

154

16

851

1.24

5.50

2.29

6.05

4.85

0.729

1.47

26.7

6.90

40.1

3.14

62.8

119

41.4

6.41

0.830

4.83

0.617

0.374

2.36

0.348

175

242

27

162

20

921

1.35

bdl

3.43

6.10

5.25

0.875

1.57

27.3

7.07

39.3

3.48

61.7

118

41.1

6.35

0.878

5.19

0.644

0.386

2.43

0.353
14 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Table 3. Chemical composition of samples from composition profiles of middle Tertiary ash-flow 

tuffs in the Seaman Range, Nevada—Continued.

Leach Canvon Formation. Narrows Member

Lower cooling unit

Sample No. 201714 201715

Upoer cooling unit

201716 201717 201718

Condor Canyon Formation

201697

Swett Tuff Member

201698 201699 201700

Major oxide compositions (weight percent)

Si02

A1203

Fe203

FeO

MgO

CaO

Na2O

K2O

Ti02

P205

MnO

Totali

LOI

74.74

13.46

0.16

0.83

0.92

1.83

2.63

5.23

0.16

bdl

0.04

99.67

5.25

75.95

12.96

0.19

0.95

0.31

1.09

3.34

4.97

0.18

bdl

0.04

99.41

0.56

73.63

13.46

0.28

1.44

0.64

1.97

3.39

4.78

0.28

0.08

0.04

99.26

1.05

72.46

13.40

0.27

1.39

0.54

2.63

4.18

4.71

0.27

0.09

0.04

99.17

3.52

70.62

13.29

0.26

1.33

0.47

5.34

3.14

5.15

0.26

0.10

0.05

99.28

3.55

73.61

14.30

0.22

1.12

0.52

0.99

3.03

5.87

0.30

bdl

0.04

99.51

4.30

72.82

14.42

0.25

1.29

0.42

1.28

3.32

5.74

0.36

0.06

0.04

99.05

3.19

69.90

16.16

0.28

1.42

1.71

2.84

2.46

4.76

0.38

0.06

0.04

99.05

9.78

67.89

17.88

0.31

1.59

2.60

3.65

1.84

3.69

0.40

0.07

0.07

99.74

14.6

Trace element compositions (parts per million)

Rb

Sr

Y

Zr

Nb

Ba

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

214

105

17

95

16

258

1.160

2.40

bdl

12.5

3.58

1.44

1.71

37.4

9.55

24.0

1.98

35.8

64.5

18.4

2.66

0.361

bdl

0.256

bdl

1.54

0.238

185

126

20

107

15

396

1.73

bdl

1.73

6.64

3.69

0.714

1.65

34.8

6.55

25.4

2.22

42.2

72.8

22.5

3.27

0.486

bdl

0.311

bdl

1.48

0.237

158

249

18

133

14

893

3.00

9.83

4.50

5.24

4.43

0.539

1.46

28.9

5.33

34.2

3.06

50.5

88.5

28.6

4.32

0.735

3.72

0.396

0.247

1.62

0.239

152

294

20

149

11

1,001

2.82

5.50

4.20

2.72

4.38

0.386

1.44

26.9

4.47

32.4

2.93

49.2

97.4

31.6

4.57

0.802

3.44

0.420

0.257

1.58

0.222

144

264

19

155

14

872

3.34

bdl

3.63

3.06

4.45

0.525

1.41

27.8

4.94

31.3

2.91

46.1

81.5

27.1

4.20

0.698

3.50

0.390

0.254

1.61

0.245

153

159

27

259

16

1,152 1

0.787

7.38

1.91

5.27

7.49

0.524

1.37

22.6

5.61

39.6

3.88

65.3

126

52.5

8.40

1.21

6.00

0.836

0.418

2.66

0.376

156

235

26

287

16

,197

1.25

11.0

bdl

5.51

7.77

0.468

1.29

21.4

5.04

43.9

4.06

60.4

121

46.3

7.42

1.30

5.95

0.757

0.406

2.52

0.367

125

297

29

291

16

937

1.43

bdl

2.69

4.68

8.26

0.552

1.41

23.7

4.41

46.7

4.62

51.9

135

41.9

7.42

1.17

5.72

0.752

0.410

2.62

0.382

107

303

27

306

20

753

1.19

bdl

1.25

11.6

8.97

0.985

1.74

45.6

5.55

48.8

4.36

70.7

149

51.6

8.34

0.954

5.97

0.718

0.445

2.65

0.382
GEOCHEMISTRY 15

Table 3. Chemical composition of samples from composition profiles of middle Tertiary ash-flow tuffs in the Seaman Range, 

Nevada—Continued.

Condor Canyon Formation

Bauers Tuff Member

Sample No. 201701 201702 201703 201704 201709

Pahranaeat Formation

201878 201879 201880

Harmony

Hills Tuff

201706 201705

Hiko Tuff

201509 201511

Major oxide compositions (weight percent)

SiO2

A1203

Fe203

FeO

MgO

CaO

Na2O

K20

TiO2

P205

MnO

Totali

LOI

72.60

14.44

0.25

1.26

0.46

1.16

3.41

6.01

0.31

0.06

0.04

99.43

3.01

71.59

15.18

0.25

1.29

0.50

1.39

3.59

5.83

0.32

bdl

0.05

98.94

1.30

71.81

14.75

0.27

1.37

0.38

1.44

3.66

5.95

0.33

bdl

0.05

98.98

0.51

71.99 71.38

14.70 14.26

0.25 0.26

1.27 1.30

0.38 0.36

1.45 2.69

3.75 3.65

5.77 5.70

0.31 0.30

0.08 0.07

0.04 0.04

99.22 99.10

0.46 1.45

75.02

13.69

0.19

0.95

1.08

1.22

2.62

4.93

0.17

0.05

0.08

99.87

4.06

73.39

12.71

0.20

1.04

0.34

3.74

3.06

5.13

0.18

0.13

0.06

99.13

2.28

78.16

11.76

0.17

0.89

0.25

1.07

2.98

4.50

0.15

bdl

0.05

99.48

0.74

63.22

15.06

0.98

4.98

3.18

4.64

2.90

3.85

0.81

0.30

0.09

99.65

2.15

64.22

14.77

0.82

4.21

2.61

5.31

3.02

3.96

0.70

0.32

0.07

99.60

1.66

69.41

15.57

0.40

2.04

1.14

2.60

3.20

4.99

0.43

0.15

0.05

99.38

2.20

69.23

14.73

0.36

1.86

1.01

4.30

3.42

4.52

0.39

0.13

0.04

99.35

0.92

Trace element compositions (parts per million)

Rb

Sr

Y

Zr

Nb

Ba

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

189

240

25

276

13

1,083

1.16

9.36

2.08

9.04

8.17

1.03

1.36

35.1

9.31

40.2

3.76

66.5

129

48.8

7.26

1.09

5.08

0.659

0.387

2.39

0.353

152

314

22

278

13

1,444

1.26

6.28

bdl

4.21

8.45

0.684

1.38

35.4

7.41

40.6

3.99

66.7

135

49.6

7.18

1.26

5.40

0.664

0.372

2.33

0.349

188

284

27

290

14

1,255

1.27

8.57

0.390

5.71

8.32

0.783

1.33

34.2

7.27

37.8

3.73

64.6

129

46.4

7.03

1.16

5.16

0.634

0.366

2.28

0.321

191 187

289 313

23 22

283 272

13 17

1,354 1,370

1.24 1.52

6.82 6.20

1.82 1,80

4.88 5.42

8.38 7.94

0.731 0.591

1.31 1.30

33.8 33.1

8.20 7.53

32.5 38.5

3.77 3.70

63.9 62.7

127 125

46.6 46.0

7.15 7.29

1.22 1.16

5.56 5.62

0.623 0.636

0.360 0.372

2.30 2.32

0.342 0.326

186

152

23

112

14

338

0.735

bdl

0.809

10.8

3.87

0.519

1.41

21.3

4.69

39.8

2.51

40.8

79.3

26.9

4.72

0.556

3.53

0.512

0.307

1.95

0.286

140

199

20

112

10

506

1.83

bdl

0.669

1.95

3.60

0.216

1.09

16.6

3.31

36.0

2.39

36.2

71.2

25.5

3.99

0.631

3.13

0.409

0.233

1.45

0.213

139

154

17

110

11

450

1.02

bdl

0.991

2.02

3.49

0.249

1.07

16.3

3.56

28.2

2.28

36.1

68.4

24.7

4.02

0.567

3.09

0.412

0.232

1.48

0.216

126

619

25

201

12

820

15.7

26.9

43.1

5.34

5.71

0.502

0.863

19.8

4.37

72.6

12.9

50.3

104

42.1

7.62

1.57

5.67

0.737

0.342

2.07

0.296

114

121

21

190

10

904

14.7

23.4

42.2

5.56

5.87

0.473

0.843

19.7

4.67

56.3

12.3

50.4

102

44.1

7.45

1.54

5.49

0.677

0.338

2.05

0.293

146

506

12

202

11

1,032

4.78

bdl

2.95

4.89

5.55

0.372

1.41

19.3

5.07

47.1

4.01

50.9

99.2

34.5

5.82

1.20

4.44

0.531

0.264

1.57

0.226

93

453

17

183

15

956

4.81

bdl

6.40

1.76

4.77

0.304

1.39

21.3

6.86

38.0

3.80

49.9

98.8

34.0

5.58

1.12

3.97

0.489

bdl

1.57

0.231
16 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Table 4. Chemical compositions of middle Tertiary ash-flow tuffs in the White River Narrows area, Nevada.

[Within unit, relative stratigraphic positions are not known. FeO/FeO* (total iron as FeO) is adjusted to 0.85. Major oxide analyses are normalized 

to 100 percent, volatile free. Totalj, original analytical (pre-normalization) total with total iron as FeiOs. LOI, loss on ignition; bdl, below detection 

limit; leaders (--), not analyzed for]

Sample No.

WahWah 

Springs

Formation

201405

Petroglyph 

Cliff

Lund Formation

201383 201392 201430

Ignimbrite Monotony Tuff

201398 201376 201461 201363

Isom Formation

Baldhills Tuff Member

201381 201466 201467 201468

Major oxide compositions (weight percent)

SiO2

A1203

Fe2O3

FeO

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

Totali

LOI

64.39

15.64

0.86

4.37

2.43

4.92

2.99

3.50

0.65

0.18

0.07

99.79

1.47

65.47

16.21

0.77

3.90

2.02

4.60

2.88

3.25

0.63

0.20

0.06

99.83

3.19

69.34

15.48

0.57

2.92

1.07

3.23

2.48

4.17

0.53

0.15

0.05

99.34

3.42

70.51

15.21

0.50

2.55

0.76

2.83

2.81

4.16

0.50

0.15

0.01

99.57

2.01

68.18

15.39

0.65

3.34

0.94

2.92

3.48

4.02

0.80

0.21

0.07

99.71

2.54

71.16

15.14

0.40

2.03

1.07

3.09

2.57

4.15

0.28

0.07

0.03

100.13

3.51

69.49 68.12

15.67 15.45

0.50 0.58

2.52 2.95

1.64 0.49

3.83 1.86

2.30 3.46

3.59 6.02

0.35 0.84

0.07 0.17

0.04 0.05

99.84 99.14

5.74 1.05

67.97

15.63

0.54

2.74

0.74

1.96

3.49

5.88

0.80

0.17

0.08

99.30

1.75

66.21

16.19

0.65

3.32

1.17

2.73

3.46

5.05

0.91

0.24

0.08

99.01

2.89

66.90

15.40

0.73

3.74

0.79

2.19

3.47

5.59

0.86

0.23

0.10

100.02

1.55

66.92

15.59

0.62

3.18

0.83

2.79

3.28

5.58

0.90

0.25

0.06

99.28

2.10

Trace element compositions (parts per million)

Rb

Sr

Y

Zr

Nb

Ba

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

126

530

24

157

13

823

14.3

22

40.9

3.71

4.97

0.364

1.22

20.5

5.06

76.3

16.1

44

93.6

36

6.64

1.34

5.66

0.711

0.366

2.18

0.320

125

601

26

204

16

839

—

-

~

—

-

-

-

-

~

~

-

~

—

_

—

-

—

—

—

-

-

167

436

21

218

20

966

5.86

14.1

14.2

5.61

5.84

0.223

1.46

21.7

3.88

68.5

5.94

60.2

118

42.3

7.65

1.36

6.20

0.718

0.307

1.73

0.250

135

412

19

208

18

1,017

—

~

~

_

-

—

—

_

~

_

-

—

—

—

—

—

—

—

-

—

—

131

400

33

311

19

1,063

—

—

—

—

~

—

—

~

~

~

~

~

..

..

—

~

..

—

~

—

—

142

354

13

146

11

1,360

-.

—

—

—

—

—

—

—

—

—

—

—

—

—

—

_

—

—

—

_

—

109 210

364 441

15 33

157 471

8 25

1,144 1,433

4.97

20

5.20

4.07

3.87

0.218

0.840

13.2

3.28

57.6

7.35

43.5

86.3

29.5

5.15

1.12

3.72

0.440

0.209

1.26

0.188

191

477

41

492

23

1,553

-

-

~

-

-

-

-

-

-

~

-

-

-

—

-

-

-

-

-

-

-

193

434

41

510

21

1,306

—

-

-

—

-

-

-

-

-

-

-

-

—

—

-

-

—

-

-

-

-

204

396

38

492

21

1,319

3.95

12

5.5

2.77

12.4

0.420

1.83

39.9

8.7

94.2

8.83

92

195

71.4

12

2.03

8.8

1.1

0.508

3.07

0.438

210

490

38

515

23

1,348

-

-

-

-

-

--

-

-

-

-

-

-

-

-

-

--

-

-

-

-

-
GEOCHEMISTRY 17

Table 4. Chemical compositions of middle Tertiary ash-flow tuffs in the White River Narrows area, Nevada—Continued.

Sample No.

Baldhills

Tuff Member

201732

Shingle Pass Tuff

lower

201473

inter.

201420

Tuff of Golden

Gate Ranee

201424 201512

Tuff of Shingle Pass

Hancock Summit Tuff, upper

201432 201453 201726 201515

Hole-in-the Leach Canyon

Wall Member Formation, upper

201713 201360 201378

Major oxide compositions (weight percent)

SiO2

A1203

Fe2O3

FeO

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

Totali

LOI

67.08

15.40

0.60

3.04

1.34

2.90

2.80

5.66

0.88

0.24

0.06

99.46

4.33

75.29

13.32

0.26

1.30

0.25

0.85

3.04

5.56

0.13

bdl

bdl

99.25

1.49

74.54

13.59

0.31

1.59

0.16

0.89

3.26

5.43

0.16

0.03

0.04

99.47

0.72

74.48

13.23

0.27

1.35

0.26

1.66

2.73

5.80

0.17

0.03

0.03

99.46

1.05

74.85

13.10

0.16

0.84

0.62

2.11

2.89

5.20

0.16

0.03

0.04

99.86

4.41

73.56

14.12

0.31

1.60

0.33

1.95

2.82

4.97

0.26

0.05

0.02

98.97

1.05

72.76 70.80

14.33 14.66

0.33 0.38

1.67 1.96

0.43 0.51

2.21 3.57

2.86 2.66

5.02 5.01

0.30 0.34

0.06 0.08

0.03 0.03

98.98 99.12

1.08 2.72

74.40

13.38

0.25

1.30

0.48

1.57

3.45

4.77

0.25

0.10

0.04

99.36

0.56

70.38

15.14

0.38

1.96

0.57

1.50

3.45

5.90

0.56

0.10

0.05

99.21

3.23

70.97

13.55

0.29

1.49

0.67

4.33

3.20

5.06

0.29

0.10

0.04

99.72

2.90

70.15

13.70

0.33

1.70

0.63

5.02

3.48

4.49

0.32

0.11

0.05

99.68

3.14

Trace element compositions (parts per million)

Rb

Sr

Y

Zr

Nb

Ba

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

218

433

37

463

25

1,218

3.93

11.4

3.9

12.7

11.5

0.729

1.76

37.3

7.98

84.5

8.5

92.7

187

74.8

11.9

2.03

8.09

1.06

0.531

3.11

0.437

232

145

20

205

17

977

0.346

bdl

bdl

6.01

6.74

0.814

1.75

33.8

6.19

50.8

5.66

67.9

96.7

50.8

7.48

1.17

5.98

0.667

0.380

2.33

0.342

210

226

38

241

19

1,594

—

—

—

-

—

—

-

-

—

—

—

-

~

—

—

—

~

—

—

_

-

157

259

20

166

14

1,363

—

—

_

-

_

—

~

-

—

—

—

-

-

—

—

—

—

—

—

_

—

193

110

12

96

13

294

~

—

—

~

—

—

—

-

—

—

—

~

—

—

—

—

—

—

—

_

-

144

352

22

209

13

2,001

1.74

bdl

12.3

3.44

5.99

0.384

0.926

27

3.69

37

3.61

97.9

182

64.2

8.66

1.61

5.22

0.655

0.348

2.08

0.298

154 142

391 567

25 23

236 248

10 14

2,058 2,161

2.17 3.01

10.7 8.39

bdl 4.55

5.15 2.89

6.37 7.41

0.499 0.310

0.883 0.865

25.5 24.5

3.46 4.42

39.4 45.3

4.05 4.58

92.3 97.5

173 188

59.1 65.4

7.98 8.59

1.66 1.74

5.06 5.70

0.66 0.645

0.345 0.316

2.08 1.92

0.283 0.277

172

203

16

147

14

727

2.63

9.17

3.06

5.43

4.11

0.584

1.48

31.4

6.25

32.7

2.69

46.8

82.1

26.3

4.16

0.686

3.20

0.414

-

1.55

0.227

180

258

29

383

18

1,176

2.36

bdl

2.52

7.62

9.65

0.925

1.33

30.5

7.93

49.4

5.90

66.1

134

53.8

8.76

1.45

6.15

0.814

0.441

2.60

0.382

151

287

19

175

14

1,153

-

-

—

--

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

131

324

21

178

15

1,266

—

-

-

-

-

-

~

-

-

-

~

-

-

-

-

-

-

-

-

-

-
18 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Table 4. Chemical compositions of middle Tertiary ash-flow tuffs in the White River Narrows area, Nevada—Continued.

Leach Canyon

Formation, upper

Sample No. 201517 201518

Condor Canvon Formation

Swett Member

201503 201504 201361

Bauers Tuff Member

201362 201365 201366 201507

Pahranagat

Formation

201707

Harmony

Hills Tuff

201368

Hiko

Tuff

201367

Major oxide compositions (weight percent)

Si02

A12C>3

Fe203

FeO

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

Totali

LOI

72.86

14.31

0.32

1.61

0.47

1.71

3.45

4.82

0.32

0.08

0.05

99.65

0.92

72.46

13.55

0.26

1.34

0.43

3.19

3.21

5.12

0.28

0.10

0.04

99.43

1.86

72.50

14.52

0.26

1.33

0.45

1.21

3.27

6.00

0.36

0.06

0.04

99.79

3.24

70.81 71.88

16.26 14.98

0.30 0.26

1.51 1.33

1.36 0.33

1.84 1.13

2.56 3.80

4.89 5.83

0.39 0.32

0.03 0.08

0.04 0.04

99.81 99.57

8.03 0.61

72.80

13.58

0.22

1.14

0.41

2.22

3.63

5.64

0.28

0.05

0.04

99.38

1.31

72.36

14.39

0.26

1.31

0.42

1.47

3.81

5.59

0.31

0.03

0.04

99.96

1.18

72.91

14.38

0.25

1.27

0.32

1.04

3.68

5.75

0.30

0.05

0.05

99.38

0.49

71.45

14.88

0.26

1.32

0.35

2.06

3.75

5.52

0.32

0.06

0.04

99.20

0.94

74.41

13.23

0.21

1.09

0.40

1.75

3.06

5.59

0.19

bdl

0.06

99.30

0.94

63.36

14.20

0.79

4.05

2.85

7.49

2.89

3.33

0.66

0.30

0.07

99.69

3.46

69.67

14.47

0.31

1.59

0.79

4.25

3.24

5.18

0.32

0.14

0.04

99.75

3.55

Trace element compositions (parts per million)

Rb

Sr

Y

Zr

Mb

Ba

Co

Ni

a

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

154

273

20

190

12

1,098

3.35

5.0

4.72

3.26

5.11

0.367

1.43

27.4

4.17

47.5

3.20

53.4

96.4

31.7

4.92

0.877

3.77

0.477

0.254

1.55

0.231

169

236

18

157

12

876

-

—

—

—

—

—

—

—

—

-

—

-

—

—

—

—

—

—

—

—

-

160

225

27

296

16

1,157

-

—

—

—

—

—

—

—

—

-

—

—

—

—

-

—

—

—

—

—

-

133 172

321 429

24 22

324 299

15 15

1,001 1,742

..

—

—

„

_

„

—

—

—

„

—

—

_

„

—

„

„

„

—

—

-

199

239

25

259

17

1,047

-

—

_

—

_

—

—

—

—

_

„

—

—

—

—

—

—

—

—

—

-

178

337

27

292

17

1,493

-

—

—

—

-

—

—

—

_

—

—

—

—

-

—

—

—

—

_

—

--

185

284

28

285

16

1,400

1.41

13

7.85

5.52

8.27

0.801

1.37

35.6

7.27

39.9

3.87

64.5

126

41.7

7.06

1.18

4.83

0.597

0.352

2.20

0.319

177

317

18

282

13

1,331

1.32

13

bdl

3.64

8.35

0.832

1.26

33.1

8.06

42.3

3.79

60.7

121

44.3

6.71

1.23

4.91

0.613

0.333

2.09

0.292

144

229

20

129

15

544

1.22

bdl

1.48

5.21

4.18

0.375

1.19

17.7

3.57

41.4

2.78

44.6

86.6

30.9

5.15

0.707

4.14

0.462

0.276

1.70

0.248

102

681

19

186

10

994

—

—

—

-

-

-

-

—

—

—

-

-

~

-

~

-

-

-

-

-

-

142

400

17

156

15

857

-

-

_

—

-

-

-

-

-

-

-

-

-

-

—

-

-

~

~

-

-
GEOCHEMISTRY 19

Table 5. Average major oxide, CIPW normative, and trace-element compositions (computed from data in tables 3 and 4) of middle 

Tertiary ash-flow tuffs in the Seaman Range, Nevada.

[FeO/FeO* (total iron as FeO) is adjusted to 0.85. Major oxide analyses are normalized to 100 percent, volatile free. LOI, loss on ignition; bdl, below 

detection limit; ±, calculated standard deviation, n is number of samples used in calculation of mean and standard deviation]

Wan Wan Springs

Formation Lund Formation

Petroglyph Cliff

Ignimbrite Monotony Tuff

Isom Formation,

Baldhills Member

Shingle Pass Tuff,

lower cooling unit

Major oxide compositions (weight percent)

n

SiO2

A1203

Fe203

FeO

MgO

CaO

Na2O

K20

TiO2

P2O5

MnO

LOI

1

64.39

15.64

0.86

4.37

2.43

4.92

2.99

3.50

0.65

0.18

0.07

1.47

7

68.08±2.24

15.64±0.57

0.63±0.13

3.21±0.67

1.25±0.53

3.79±0.79

2.66±0.16

3.96±0.46

0.57±0.07

0.18±0.03

0.05±0.02

3.04±0.49

4

66.57±2.48

15.83±0.52

0.71±0.09

3.65±0.45

1.31±0.51

3.87±1.44

3.19±0.21

3.72±0.51

0.85±0.05

0.24±0.05

0.07±0.03

2.48±0.49

7

70.55±0.84

15.37±0.20

0.44±0.06

2.25±0.28

1.25±0.25

3.34±0.33

2.46±0.10

3.89±0.24

0.32±0.05

0.08±0.01

0.04±0.01

4.07±1.00

6

67.20±0.73

15.61±0.30

0.62±0.07

3.16±0.35

0.89±0.31

2.41±0.45

3.32±0.27

5.63±0.33

0.86±0.04

0.22±0.03

0.07±0.02

2.28±1.18

3

75.00±0.32

13.40±0.19

0.27±0.02

1.39±0.08

0.25±0.07

0.95±0.08

3.01±0.11

5.60+0.03

0.14±0.01

bdl

bdl

1.42±0.42

CIPW norms (weight percent)

Q

C

or

ab

an

di

hy

mt

il

ap

17.98

0.00

20.66

25.34

18.90

3.55

10.66

1.24

1.24

0.44

25.95

0.53

23.38

22.47

17.62

0.00

7.64

0.91

1.08

0.42

22.03

0.10

21.98

27.00

17.61

0.00

8.08

1.04

1.61

0.57

31.06

1.23

22.97

20.79

16.07

0.00

6.43

0.64

0.62

0.19

18.62

0.20

33.28

28.13

10.50

0.00

6.23

0.90

1.64

0.52

32.73

0.67

33.09

25.44

4.70

0.00

2.72

0.39

0.27

0.00

Trace element compositions (parts per million)

n

Rb

Sr

Y

7s

Nb

Ba

n

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

1

126

530

24

157

13

823

1

14.3

22.0

40.9

3.71

4.97

0.364

1.22

20.5

5.06

76.3

16.1

44.0

93.6

36.0

6.64

1.34

5.66

0.711

0.366

2.18

0.320

27

156±22

456±63

19±3

189±22

14±3

895±78

5

7.51±2.81

7.84±5.68

9.44±6.06

10.2±4.97

5.89±0.22

0.262±0.06

1.37±0.12

20.2±1.20

3.88±0.43

62.2±6.72

8.14±3.28

57.2±3.57

115±6.02

43.4±2.48

7.39±0.47

1.39±0.11

5.63±0.35

0.682±0.04

0.304±0.04

1.76±0.21

0.255±0.03

7

110±25

476±97

32±5

311±25

18±2

990±104

3

5.89±2.21

12.0±1.79

5.16±1.80

2.75±0.54

7.36±0.61

0.377±0.06

1.32±0.12

15.5±1.36

3.90±0.21

66.3±15.5

13.2±0.81

52.7±4.90

107±7.81

46.4±4.55

8.49±0.76

1.64±0.11

6.54±0.79

0.939±0.09

0.503+0.06

3.14±0.39

0.443±0.06

9

124±11

370±25

17±4

139±9

9±3

1,263±77

6

4.29±0.75

6.31±8.04

4.87±0.64

6.88±4.19

3.93±0.15

0.174±0.04

0.905±0.13

13.4±1.08

3.53±0.41

50.3±5.40

6.52±0.82

46.0+3.94

90.0±8.12

34.6±3.68

5.54±0.39

1.19±0.05

3.97±0.19

0.475±0.04

0.235±0.02

1.48±0.21

0.216±0.03

11

209±12

425±62

39±3

493±29

23±1

1,357±92

2

3.94±0.01

11.7±0.43

4.70±1.13

7.74±7.02

12.0±0.64

0.575±0.22

1.80±0.05

32.6±1.55

8.34±0.51

89.4±6.86

8.67±0.23

92.4±0.50

191±5.65

73.1±2.41

12.0±0.07

2.03±0.00

8.45±0.50

1.08±0.03

0.520±0.02

3.09±0.03

0.438±0.00

11

223±7

144±13

33±6

204±11

17±2

1,012±107

3

0.430+0.09

3.47±6.01

0.990+0.88

6.65±0.80

6.92±0.30

0.965+0.14

1.71 ±0.04

33.3+0.90

6.50±0.51

50.3+2.73

5.71+0.17

71.1+3.88

126+28.2

52.2+2.96

8.16+0.68

1.25±0.12

4.02+3.49

0.790±0.11

0.494±0.00

2.77+0.38

0.400+0.05
20 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Table 5. Average major oxide, CIPW normative, and trace-element compositions (computed from data in tables 3 and 4) of middle 

Tertiary ash-flow tuffs in the Seaman Range, Nevada—Continued.

Shingle Pass Tuff,

intermediate

cooling unit

Shingle Pass Tuff,

Tuff of the

Golden Gate Range

Tuff of

Hancock Summit

upper

cooh'ng unit

Isom Formation, Leach Canyon Formation,

Hole-in-the-Wall

Member

Narrows Member,

lower cooling unit

Major oxide compositions (weight percent)

n

SiO2

A12O3

Fe2O3

FeO

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

LOI

3

74.16+0.77

13.55±0.06

0.32±0.01

1.64+0.06

0.30+.0.16

1.26±0.53

3.08+0.15

5.44±0.01

0.18+0.02

0.03+0.03

0.03+0.01

1.22±0.54

4

75.81+1.44

12.83±0.48

0.21±0.04

1.07±0.22

0.36±0.17

1.48+0.51

2.71+0.13

5.36+0.32

0.14±0.04

0.01+0.01

0.02+0.02

1.87±1.70

3

72.37+1.42

14.37±0.27

0.34±0.04

1.75±0.19

0.42+0.09

2.58+0.87

2.78+0.10

5.00±0.03

0.30±0.04

0.07±0.02

0.03±0.01

1.62±0.96

6

74.26+0.65

13.66±0.50

0.24±0.02

1.21+0.08

0.50±0.22

1.62+0.43

2.94+0.35

5.33±0.31

0.18+0.04

0.02+0.04

0.05+0.01

2.63±1.98

1

70.38

15.14

0.38

1.96

0.57

1.50

3.45

5.90

0.56

0.10

0.05

3.23

2

75.34+0.86

13.21+0.35

0.17+0.02

0.89+.0.09

0.62+.0.43

1.46±0.52

2.99+0.50

5.10±0.18

0.17±0.02

bdl

0.04+0.00

2.91+3.32

CIPW norms (weight percent)

Q

C

or

ab

an

di

hy

mt

il

ap

31.20

0.38

32.15

26.10

6.03

0.00

3.26

0.47

0.35

0.07

35.20

0.00

31.65

22.93

7.02

0.18

2.41

0.31

0.27

0.03

30.05

0.00

29.56

23.52

11.95

0.35

3.35

0.50

0.57

0.15

31.77

0.14

31.50

24.88

7.94

0.00

3.04

0.34

0.35

0.04

22.86

0.60

34.86

29.15

6.78

0.00

3.87

0.56

1.07

0.25

33.82

0.12

30.13

25.26

7.26

0.00

2.82

0.25

0.32

0.00

Trace element compositions (parts per million)

n

Rb

Sr

Y

Zr

Nb

Ba

n

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

11

203±11

201±16

33±4

218±26

17±3

1,400±173

2

1.44±0.70

4.36+6.17

2.27±3.20

5.60±0.34

7.18±0.53

0.850±0.31

1.57±0.18

30.2±4.60

5.78±1.21

39.1±9.05

5.85+0.47

73.2±13.7

135±14.8

52.6±7.85

8.35±1.39

1.36±0.11

6.46+0.87

0.859±0.09

0.480±0.04

2.94+0.25

0.422+0.04

28

180±23

160±51

23±6

124±21

13±2

746±411

2

0.829+0.31

2.80±3.96

1.15+0.88

3.87±0.73

4.11+0.74

0.378+0.09

1.13+0.26

23.9±1.63

3.67+1.08

29.7±0.28

2.26±0.12

45.3±24.3

83.9±42.6

36.4±13.3

6.21±0.75

0.893±0.39

4.44±0.28

0.616+0.06

0.323±0.00

2.12+0.28

0.303+0.03

9

162±22

387±79

24±2

246±28

14±2

1,999±289

3

2.31+0.65

6.36±5.63

5.62+6.22

3.83±1.18

6.59±0.74

0.398±0.10

0.891+0.03

25.7+1.26

3.86±0.50

40.6+4.27

4.08±0.49

95.9±3.13

181±7.55

62.9±3.35

8.41+0.37

1.67±0.07

5.33±0.33

0.653+0.01

0.336+0.02

2.03+0.09

0.286±0.01

8

191±13

209±18

24±5

154±6

16±2

863±70

6

1.44+0.59

5.51±3.07

2.53±0.72

6.00±0.36

4.96+0.45

0.686+0.22

1.54+0.06

28.3±1.72

6.18+0.86

35.8±3.29

3.11±0.26

61.1+7.33

115±16.9

39.9+6.79

6.15+1.01

0.837+0.08

4.92+1.05

0.595±0.09

0.392+0.01

2.23+0.38

0.334±0.05

7

179+14

281±92

31±5

358+46

18+5

1,144±112

1

2.36

bdl

2.52

7.62

8.15

0.925

1.33

30.5

7.93

49.4

5.90

66.1

134

53.8

8.76

1.45

6.15

0.814

0.441

2.60

0.382

4

198±15

121±20

24±7

101 ±5

14±2

356±70

2

1.45±0.40

1.20±1.70

0.865±1.22

9.57±4.14

3.64+0.08

1.08+0.51

1.68+0.04

36.1+1.84

8.05+2.12

24.7+0.99

2.10±0.17

39.0±4.52

68.7±5.87

20.5±2.90

2.97+0.43

0.424±0.09

bdl

0.283±0.04

bdl

1.51+0.04

0.237±0.00
GEOCHEMISTRY 21

Table 5. Average major oxide, CIPW normative, and trace-element compositions (computed from data in tables 3 and 4) of middle 

Tertiary ash-flow tuffs in the Seaman Range, Nevada—Continued.

Leach Canyon Formation,

Narrows Member,

upper cooling unit

Condor Canyon Formation

Swett Tuff Member Bauers Tuff Member

Pahranagat

Formation

Harmony Hills

Tuff

Hiko

Tuff

Major oxide compositions (weight percent)

n

Si02

A1203

Fe203

FeO

MgO

CaO

Na2O

K2O

Ti02

P2O5

MnO

LOI

7

71.88*1.30

13.61±0.33

0.29±0.03

1.47±0.14

0.55±0.10

3.46±1.46

3.43±0.35

4.88±0.24

0.29±0.02

0.10±0.01

0.05±0.01

2.42±1.13

6

71.25±2.14

15.59±1.43

0.27±0.03

138±0.17

1.17±0.88

1.97*1.06

2.75±0.57

5.16±0.88

0.37±0.03

0.05±0.03

0.05±0.01

7.19+4.52

10

72.08±0.55

14.55±0.45

0.25±0.01

1.29+0.06

0.39±0.06

1.61*0.54

3.67±0.12

5.76±0.15

0.31±0.01

0.05±0.03

0.04±0.00

1.13*0.76

4

75.25±2.05

12.85±0.83

0.19+0.02

0.99+0.09

0.52±0.38

1.95*1.23

2.93±0.21

5.04±0.45

0.17±0.02

0.05±0.06

0.06±0.01

2.00+1.53

3

63.60±0.54

14.67+0.44

0.87±0.10

4.41±0.50

2.88±0.29

5.82+1.49

2.94±0.07

3.71±0.34

0.72+0.08

0.31+0.01

0.08+0.01

2.42+0.93

3

69.44±0.22

14.93±0.57

0.36±0.04

1.83*0.23

0.98±0.18

3.71±0.97

3.29+0.12

4.90±0.34

0.38±0.06

0.14±0.01

0.04±0.01

2.22*1.32

CIPW norms (weight percent)

Q

C

or

ab

an

di

hy

rat

il

ap

26.32

0.00

28.84

29.05

7.30

6.86

0.43

0.42

0.55

0.23

28.90

2.02

30.47

23.23

9.46

0.00

4.72

0.39

0.70

0.11

24.31

0.00

34.04

31.08

6.21

1.21

2.08

0.37

0.59

0.12

33.93

0.00

29.76

24.81

7.02

1.94

1.82

0.28

0.33

0.11

15.92

0.00

21.93

24.83

15.90

9.00

9.06

1.25

1.37

0.73

22.71

0.00

28.94

27.80

11.52

4.96

2.50

0.52

0.73

0.33

Trace element compositions (parts per million)

n

Rb

Sr

Y

Zr

Nb

Ba

n

Co

Ni

Cr

Cs

Hf

Sb

Ta

Th

U

Zn

Sc

La

Ce

Nd

Sm

Eu

Gd

Tb

Tm

Yb

Lu

14

151±12

259±34

18+4

153±22

13±1

958±155

4

3.13±0.26

5.08±4.02

4.26±0.47

3.57±1.14

4.59+0.35

0.454±0.09

1.44±0.02

27.8±0.85

4.73±0.51

36.4±7.53

3.03±0.13

49.8±3.03

91.0+7.45

29.8+2.28

4.50±032

0.778±0.08

3.61±0.16

0.421±0.04

0.253±0.00

1.59+0.03

0.234±0.01

8

144±20

251±54

27±2

295±18

16±2

1,081±170

4

1.16*0.27

4.60+5.51

1.46*1.14

6.77±3.24

8.12±0.65

0.632+0.24

1.45*0.20

28.3*11.6

5.15±0.56

44.8±3.98

4.23±0.33

62.1±7.98

133+12.3

48.1±4.94

7.90±0.55

1.11*0.16

5.91±0.13

0.766±0.05

0.420*0.02

2.61±0.06

0.377±0.01

24

183+12

298±47

25+3

283±24

15+2

1.288*183

7

1.31*0.12

9.03+2.95

1.99+2.74

5.49+1.74

8.27*0.17

0.779±0.14

1.33*0.04

34.3*1.05

7.86±0.74

38.0+3.96

3.80+0.10

64.2±2.09

127±4.32

46.2+2.66

7.10+0.20

1.19+0.06

5.12+0.52

0.632±0.02

0.363±0.02

2.27+0.10

0.329±0.02

13

169±28

151±48

23±7

114±11

14±3

390±118

4

1.20+0.46

bdl

0.987±0.35

5.00±4.16

3.79+0.31

0.34±0.14

1.19*0.16

18.0+2.30

3.78±0.62

36.3±5.88

2.49+0.22

39.4+4.09

76.4±8.24

27.0+2.75

4.47±0.57

0.615±0.07

3.47±0.49

0.449±0.05

0.262±0.04

1.65*0.23

0.241±0.03

8

122±12

585±99

20+.4

194±10

13±3

975±114

2

15.2+0.71

25.2+2.48

42.7+0.64

5.45±0.16

5.79±0.11

0.488±0.02

0.853±0.01

19.8+0.07

4.52±0.21

64.5+11.5

12.6±0.43

50.4±0.08

103*1.41

43.1+1.41

7.54±0.12

1.56*0.02

5.58±0.13

0.707±0.04

0.340±0.00

2.06±0.01

0.294±0.00

7

133±20

469±39

16±2

180±20

13±2

994±72

2

4.80±0.02

bdl

4.68±2.44

3.33±0.17

5.16±0.55

0.34±0.05

1.40+0.01

18.8+3.54

5.97*1.27

42.6+6.43

3.91*0.15

50.4±0.71

99.0+0.29

34.3±0.35

5.70±0.17

1.16*0.06

4.21±0.33

0.510±0.03

0.264+0.00

1.57*0.00

0.228+0.00
22 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Figure 8. Uppermost part of the upper cooling unit of the Narrows Member (LCU) of the Leach Canyon Formation, the 

Swett Tuff Member of the Condor Canyon Formation (CS), the Bauers Tuff Member of the Condor Canyon Formation(CB), 

the Pahranagat Formation (PF), and the Harmony Hills Tuff (HH). View to the southwest. Section is on the west side of 

White River Narrows midway along its length. Note vitrophyres several meters thick at the base of the Swett Tuff and 

Bauers Tuff Members.

and lithic and pumice contents), and are characterized by 

compositional attributes similar to those of subalkaline continental interior subduction-related volcanic rocks (Macdonald and others, 1992).

Pearce and others (1984) recognized that granitoid 

rocks generated in various tectonic settings have distinctive 

geochemical signatures on trace-element discriminant diagrams. Trace-element abundance variations in coeval volcanic and plutonic rocks generated in a given terrane should 

be similar. Consequently, compositions of tuffs of the Narrows area can be compared to the tectonic setting-trace element grids developed by Pearce and others (1984). Traceelement data for the tuffs plot in the volcanic arc field, near 

its boundary with within-plate compositions, on these diagrams (fig. 10). Compositions of Narrows area tuffs plotting near the within-plate field may indicate that the 

associated magmas had a significant crustal component. 

Gill (1981) indicated that Ba/Nb ratios of modern arc rocks 

are greater than 26. Ba/Nb ratios for all tuffs of the Narrows 

area are greater than 26 and for most units are greater than 

50. Major oxide compositions for tuffs of the Narrows area 

follow a calc-alkaline trend on an AFM diagram (fig. 11). 

All of these compositional features support the inference 

that tuffs of the Narrows area are subduction-related

continental arc magmas. Furthermore, the compositions of 

ash-flow tuffs of the southeastern Great Basin are similar to 

those reported by Macdonald and others (1992) for obsidians from subduction-related volcanic centers in continental 

interior settings. Differences between the two data sets 

reflect the fact that the data set of Macdonald and others 

(1992) is biased toward rhyolitic compositions. As a consequence, some of the dacitic ash-flow tuffs of the southeastern Great Basin are characterized by compositions 

somewhat less evolved, and having relatively lower and 

higher abundances of the incompatible and compatible elements, respectively, than those of the obsidians.

Zirconium abundances for most of the tuffs of the Narrows area approximate the experimentally determined (Watson and Harrison, 1983) zirconium saturation threshold of 

several hundred parts per million. Thus, magmas represented 

by these tuffs did not equilibrate with peralkaline liquids nor 

did they equilibrate at a temperature greater than about 

860°C. Zirconium abundances in the Baldhills and Hole-inthe-Wall Members of the Isom Formation, however, are 

greater than 350 ppm. These tuffs have compositions with 

alkaline tendencies, and they may have equilibrated with 

peralkaline liquids and (or) at temperatures greater than 

about 860°C.
GEOCHEMISTRY 23

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Si0 2 , IN WEIGHT PERCENT

78

Figure 9. Variation diagrams showing abundances of selected major oxides and trace elements in ash-flow tuffs in the White River Narrows area, Nevada. Abundances given in tables 3 and 4.
24

1 ,000

OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

100

10

WITHIN PLATE

VOLCANIC ARC

10 100 

YTTRIUM, IN PARTS PER MILLION

10,000

1 ,000-

100 -

1 10 100 1,000 

B YTTRIUM+NIOBIUM, IN PARTS PER MILLION

Figure 10. Trace element-tectonic setting discrimination variation diagrams showing average compositions of ash-flow tuffs in 

the White River Narrows area, Nevada. Tectonic setting-composition boundaries from Pearce and others (1984); compositions from 

table 5. Symbols as in figure 2. A, Niobium versus yttrium. B, Rubidium versus yttrium plus niobium.

Feldspar-melt distribution coefficients for strontium, 

barium, and rubidium (Hanson, 1978) are such that feldspar 

fractionation preferentially removes strontium and then barium from the melt phase relative to rubidium such that residual 

liquids become progressively enriched in rubidium relative to 

barium and strontium. Rubidium abundances increase systematically with increasing SiC>2 (fig. 9) and deceasing 

strontium abundances (fig. 12). Rubidium enrichment,

Figure 11. Ternary AFM (Al2O3-FeO-MgO) diagram showing 

compositions of ash-flow tuffs in the White River Narrows area, 

Nevada. Symbols as in figure 2. Dots show all data from tables 3 

and 4; other symbols show average tuff compositions from table 

5. Cascade calc-alkaline trend line from Irvine and Baragar (1971).

250

200

- 150

100

O

A

x

A

n

o

O

100 200 300 400 500 600 

STRONTIUM, IN PARTS PER MILLION

700

Figure 12. Variation diagram showing the average rubidium and 

strontium abundances in ash-flow tuffs in the White River Narrows 

area, Nevada. Symbols as in figure 2; abundances from table 5.

relative to strontium and barium abundances (fig. 13), in tuffs 

of the Narrows area is not as pronounced as in some high-silica 

rhyolites, in which the abundance of rubidium may greatly 

exceed the abundances of strontium and barium (Hildreth, 

1979; Duffield and du Bray, 1990). Barium abundances in
GEOCHEMISTRY 25

RB SR

Figure 13. Ternary variation diagram showing the average relative proportions of rubidium, barium, and strontium in ash-flow 

tuffs in the White River Narrows area, Nevada. Symbols as in figure 2; abundances from table 5.

1 ,000-,

Rb Ba Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y Tm Yb

Figure 14. Chondrite-normalized (after Thompson and others, 

1983) extended trace-element diagram showing average compositions of ash-flow tuffs in the White River Narrows area, Nevada. 

Trace elements are arranged in order of increasing compatibility to 

the right. Trace-element abundances from table 5.

most of the analyzed tuffs are elevated, considerably in some 

cases, relative to barium abundances in obsidians from 

subduction-related volcanic rocks (Macdonald and others, 

1992). Rb/Sr ratios range from a low of 0.18 in the Harmony 

Hills Tuff to a more evolved value of 1.64 in the lower ashflow tuff of the Leach Canyon Formation; the average Rb/Sr 

value for the 18 analyzed tuffs is 0.68±0.45.

Chondrite-normalized extended trace-element patterns 

(table 5, fig. 14) for tuffs of the Narrows area are gently

La Ce Sm Eu Gd Tb Tm Yb Lu

Figure 15. Chondrite-normalized (after Anders and Ebihara, 

1982) rare earth element diagram showing average compositions of ash-flow tuffs in the White River Narrows area, Nevada. Rare earth element abundances from table 5.

negatively sloping and relatively smooth and show superposed negative Ba, Nb, Ta, Sr, P, and Ti anomalies. The barium and strontium anomalies probably reflect feldspar 

fractionation, whereas the phosphorous and titanium anomalies may indicate apatite and iron-titanium-oxide fractionation, respectively. A negative niobium-tantalum anomaly is 

considered (Wood and others, 1979; Gill, 1981; Pearce and 

others, 1984) to be an indication of subduction-related arc 

magmatism. The shape, slope, and abundance levels of 

chondrite-normalized extended trace-element patterns for 

tuffs of the Narrows area overlap those for the East-Central 

Nevada and Indian Peak volcanic fields (Gans and others, 

1989; Best and Christiansen, 1991; Feeley and Grunder, 

1991).

The most striking features of trace-element patterns for 

tuffs of the Narrows area are their parallelism and their relatively limited compositional range. In addition, patterns for 

samples from the composition profiles of individual stratigraphic units define remarkably narrow trace-element abundance ranges; compositional variation within each of the 

tuffs of the Narrows area is relatively limited (table 3). Indices of compositional evolution, abundances of SiO2 or 

rubidium, for instance, are poorly correlated with abundances of other oxides and trace elements shown in the 

trace-element diagram. The greatest amounts of compositional variation are among phosphorous, titanium, barium, 

and strontium and probably only reflect varying amounts of 

apatite, iron-titanium oxide, and plagioclase fractionation. 

Tuffs of the Isom compositional type are distinguished by 

the largest abundances of the most compatible trace elements (table 3, fig. 14). The most evolved tuffs, the 

Pahranagat Formation and the lower cooling unit of the 

Narrows Member of the Leach Canyon Formation, are distinguished by large negative barium anomalies that, again, 

probably reflect feldspar fractionation.
26 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

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STRONTIUM, IN PARTS PER MILLION

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ZIRCONIUM, IN PARTS PER MILLION

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NIOBIUM, IN PARTS PER MILLION

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BARIUM,__ IN PARTS PER MILLION
27

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Figure 16 (above and facing page). Stratigraphic compositional variation of ash-flow tuffs in the White River Narrows area, Nevada. 

Asterisks (*) represent data for samples collected without regard to vertical position within the indicated units; X's represent data for 

samples from composition profiles. Analytical uncertainty for oxide or element is shown by error bars in bottom right corner of plot. Units 

arranged from youngest (top) to oldest (bottom) in each plot. Unit designations as in figure 2.
28 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

LUND FORMATION 

201454/201456

o 2

SHINGLE PASS TUFF 

INTERMEDIATE COOLING UNIT 

201729/201728

SHINGLE PASS TUFF 

UPPER COOLING UNIT 

201725/201724

Na Al P Ca Ti Mn Co Zn Sr Zr Sb Ba Ce Sm Gd Tm Lu Ta U 

Mg Si K Sc Cr Fe Ni Rb Y Nb Cs La Nd Eu Tb Yb Hf Th

PETROGLYPH CLIFF IGNIMBRITE 

201458/201460

SHINGLE PASS TUFF 

LOWER COOLING UNIT 

201731/201730

TUFF OF THE 

GOLDEN GATE 

RANGE 

201727/201447

LEACH CANYON FORMATION 

NARROWS MEMBER 

LOWER COOLING UNIT 

201714/201715

Na' Al' P ' Ca' Ti ' Mn' Co' Zn ' Sr' Zr' Sb ' Ba' Ce's'm' Gd' Tm' Lu' fa' U 

Mg Si K Sc Cr Fe Ni Rb Y Nb Cs La Nd Eu Tb Yb Hf Th

Average (table 5) chondrite-normalized rare earth element patterns for tuffs of the Narrows area (fig. 15), similar 

to the chondrite-normalized extended trace-element patterns, define a narrow compositional range; similarly, compositional variation within each of tuffs is relatively limited 

(table 3). The light rare earth element parts of the patterns are 

moderately negatively sloping, whereas the heavy rare earth 

element parts are only very gently negatively sloping; the

patterns include small negative europium anomalies of variable magnitude that probably result from modest amounts of 

feldspar fractionation (Hanson, 1978). Chondrite-normalized La/Lu ratios range from 12.3 to 34.8 and average 

19.5±4.9, and total rare earth element contents range from 

133.5 to 384.0 (average 233.9±65.3) ppm.

Systematic time-space-composition variations characterize ash-flow tuffs erupted from sources within the three
GEOCHEMISTRY 29

LEACH CANYON FORMATION 

NARROWS MEMBER 

UPPER COOL ING UNIT 

201716/201718

CONDOR CANYON FORMATION 

BAUERS TUFF MEMBER 

201701/201709

HARMONY HILLS TUFF 

201706/201705

Na A l' P ' Ca' f i ' Mn' Co' z'n ' s'r' z'r' Sb ' Ba' Ce's'm' Gd' fm Lu' fa' U 

Mg Si K Sc Cr Fe N! Rb Y Nb Cs La Nd Eu Tb Yb Hf Th

CONDOR CANYON FORMATION 

SWETT TUFF MEMBER 

201697/201700

Na' A I' P ' Ca' T i ' Mn' Co' Zn ' Sr' Zr' Sb ' Ba' Ce's'm' Gd ' fm' Lu' fa' U 

Mg Si K Sc Cr Fe Ni Rb Y Nb Cs La Nd Eu Tb Yb Hf Th

Figure 17 (above and facing page). Enrichment-depletion factors (solid bars) for 14 ash-flow tuffs in the White River Narrows area, Nevada. Factors calculated from compositions of stratigraphically lowest and highest samples in composition profiles. Data for the Bishop Tuff 

are shown for comparison (diagonal-ruled bars). Dots on the baseline at a value of 1.0 indicate oxides or elements whose abundances are 

below detection limits or are identical within analytical uncertainty. Six-digit numbers in upper left corner of each plot indicate stratigraphically low and high samples (table 3), respectively.

caldera complexes of the southeastern Great Basin (fig. 16). 

Specifically, tuffs erupted from sources within the Indian 

Peak caldera complex, which reflect the earliest manifestation of voluminous middle Tertiary magmatism in the 

Narrows region, are characterized by distinctly lower abundances of SiC>2, K2O, rubidium, and thorium and higher abundances of A12O3 , FeO*, MgO, TiO2 , P2O5 , strontium, cobalt, 

and scandium relative to tuffs erupted from younger sources 

in either the Central Nevada or Caliente caldera complexes. 

No systematic compositional differences are apparent 

between tuffs erupted from the Central Nevada or Caliente 

caldera complexes, though some systematic compositional 

variation with respect to age characterizes these tuffs. In particular, abundances of SiC>2, K^O, rubidium, zinc, ytterbium,

and tantalum generally decrease in progressively younger 

tuffs erupted from the these two caldera complexes.

VERTICAL ZONATION

Smith (1979) and Hildreth (1979, 1981), among others, 

have argued convincingly that most if not all large, highly 

evolved magma systems, particularly those associated with 

caldera-forming eruptions, are vertically compositionally 

zoned. Most zoned ash-flow tuffs are interpreted to represent 

eruption from vertically zoned reservoirs; the base and top of 

such tuffs are interpreted to represent the shallowest and 

deepest erupted levels, respectively, of the source reservoir.
30 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

Table 6. Summary of enrichment and depletion relations for ash-flow tuff units exposed in the Seaman 

Range, Nevada.

[Numbers in the Enriched, Depleted, and Unchanged columns under the Early/Late heading indicate the number of units 

(of 14 total units) in which the abundance of the indicated oxide or element is enriched, depleted, or unchanged, 

respectively, in stratigraphically lowest sample versus that for highest sample. Similarly, numbers in the Enriched, 

Depleted, and Unchanged columns under the Transitions heading indicate the number of instances (of 29 total upsection 

within-unit transitions) in which the abundance of the indicated oxide or element is enriched, depleted, or unchanged, 

respectively, relative to that of the within-unit sample collected directly above. In both sets of columns, oxides and 

elements are arranged, from top to bottom, in order of decreasing enrichment in the top of the magma reservoir 

(stratigraphically low in the vertical section of each tuff) or, alternatively, in order of increasing enrichment in 

progressively lower parts of the magma reservoir (stratigraphically high in the composition profile of each tuff)]

Oxide or 

element

Rb

Ta

Sb

U

Cs

Tb

Gd

Yb

Nb

MgO

SiO2

K2O

Th

La

Ce

Sm

Tm

Zn

Nd

A1203

Hf

Lu

Ni

Sc

Eu

MnO

Y

Cr

TiO2

Zr

Ba

P205

Na20

FeO*

CaO

Sr

Co

Enriched

13

12

12

12

11

10

9

9

8

9

8

8

8

8

8

8

6

8

8

7

7

7

3

7

7

6

6

5

6

6

6

2

5

5

4

3

2

Earlv/Late

Depleted

1

1

2

2

3

3

2

2

3

5

4

4

5

5

5

5

3

6

6

6

6

6

2

7

7

6

6

7

8

8

8

5

8

9

10

11

12

Unchanged

.

1

-

-

-

1

1

3

3

-

2

2

1

1

1

1

5

.

.

1

1

1

9

.

-

2

2

2

1

-

.

7

1

-

.

_

-

Oxide or 

element

Rb

Ta

SiO2

Cs

U

Ni

La

Gd

A12O3

Sb

MgO

Tb

Yb

Lu

Nb

MnO

Nd

Zn

Th

Sm

Y

Hf

Ce

Eu

K2O

TiO2

Na20

Cr

Ba

Tm

Sc

P205

Zr

Sr

FeO*

Co

CaO

Enriched

19

16

19

18

16

15

13

12

17

17

16

12

11

6

8

11

13

11

10

10

10

10

10

12

14

10

12

12

11

15

7

9

6

9

10

5

8

Transitions

Depleted

4

5

9

9

9

8

6

5

11

12

11

7

6

2

5

9

11

9

8

8

9

9

10

12

15

12

14

14

14

12

11

13

13

18

19

15

20

Unchanged

6

8

1

2

4

6

10

12

1

-

2

10

12

21

16

9

5

9

11

11

10

10

9

5

-

7

3

3

4

2

11

7

10

2

-

9

1

The resulting rocks provide an inverted view of pre-emption 

compositional gradients within source magma reservoirs.

Hildreth (1979) pioneered the use of enrichment-depletion diagrams in the evaluation of compositional variation 

within ash-flow tuffs. The composition of the earliest 

erupted magma is normalized to that of the latest erupted 

magma, and the resulting values, which identify the magnitude and direction of pre-eruption vertical compositional 

gradients within the reservoir, are graphically portrayed to

create an image of compositional variation within the 

magma reservoir. Geochemical data for samples from 

compositional profiles of tuffs of the Narrows area were processed accordingly. In most cases, the composition of the 

sample from the lowest stratigraphic position (representing 

the earliest erupted, top of the magma reservoir) in the compositional profile of each unit was divided by that of the 

highest (latest erupted, relatively lower part of the magma 

reservoir). Vertical enrichment-depletion factors for 14 of
GEOCHEMISTRY 31

-10 No Al P Co Ti Mn "Co Zn Sr 

Mg Si K Sc Cr Fe Ni Rb

Zr Sb Ba Ce Sm Gd Tm Lu Ta U 

f Nb Cs La Nd Eu Tb Yb Hf Th

Figure 18. Histogram showing enrichment-depletion abundance behavior of oxides and elements in samples from composition profiles of the ash-flow tuffs in the White River Narrows area, 

Nevada. The height of each bar represents the number of instances 

(maximum of 14 possible; 1 per stratigraphic unit) in which the indicated oxide or element is enriched (early/late>l) minus the number of instances in which the indicated oxide or element is depleted 

(early/late<l), as compiled from figure 17 and table 6. Dots on 

zero baseline indicate oxides or elements that are enriched and depleted in the same number of units.

FIT

~ 10 No Al P 

Mg Si

Ti Mn Co Zn S 

c Cr Fe Ni Rb

Zr Sb Ba Ce Sm Gd Tm Lu Ta U 

C Nb Cs La Nd Eu Tb Yb Hf Th

Figure 19. Histogram showing within-unit enrichment-depletion abundance behavior of oxides and elements in composition 

profile sample suites of ash-flow tuffs in the White River Narrows 

area, Nevada. The height of each bar represents the number of 

samples (maximum of 29 possible) in which the abundance of the 

indicated oxide or element is enriched relative to that in the immediately higher (stratigraphically), within-unit sample minus the 

number of samples in which the abundance of the indicated oxide 

or element is depleted relative to that of the immediately higher, 

within-unit sample. Dots on the zero baseline indicate elements 

that are enriched and depleted in the same number of samples.

the Narrows area tuffs were obtained (fig. 17). In three cases 

(discussed following), compositional variation for a number 

of major oxide or trace elements in the stratigraphically 

highest sample reverses enrichment-depletion trends 

depicted by other samples from the compositional profile of 

that unit. These samples were excluded from enrichmentdepletion factor computation.

Hildreth (1979) demonstrated that a number of oxides 

and elements, including Na2O, MnO, Rb, Y, Nb, Cs, heavy 

rare earth elements, Ta, Th, and U, were concentrated in the 

top of the magma reservoir represented by the Bishop Tuff, 

whereas a number of others, including CaO, TK>2, FeO*, 

cobalt, strontium, zirconium, barium, and light rare earth elements were depleted in the top of the magma reservoir. Similar zonation patterns have been defined for many high-silica 

systems. Eruption of progressively deeper levels from 

magma reservoirs zoned in this fashion results in a "normally zoned" ash-flow tuff. Most of tuffs of the Narrows 

area are normally zoned; the Monotony Tuff is reversely 

zoned for many elements. Zonation patterns defined for a 

number of oxides and elements in tuffs of the Narrows area 

are, however, either inconsistent between the various stratigraphic units that they represent or opposite in direction to 

those for the Bishop and other similar high-silica tuffs. In 

addition, it is particularly noteworthy that the magnitudes of 

enrichments and depletions computed for various oxides and 

elements in tuffs of the Narrows area are significantly 

smaller than those for high-silica systems such as the Bishop 

Tuff (Hildreth, 1979). Zonation data for tuffs of the Narrows 

area can be summarized in several ways.

The number of tuffs of the Narrows area for which the 

abundances of each oxide or element is upward enriched, 

depleted, or unchanged (within analytical uncertainty) was 

compiled (table 6) from enrichment-depletion diagrams (fig.

17) in order to evaluate the consistency of between-unit 

oxide or element behavior. The difference between the number of enrichments and depletions, for each oxide or element 

in tuffs of the Narrows area, was computed and plotted (fig.

18) as a histogram in the form of an enrichment-depletion 

diagram. Accordingly, oxides and elements whose compositions are most systematically upward enriched or depleted 

can be identified. Surprisingly, very few oxides or elements 

are consistently either upward enriched or depleted in tuffs 

of the Narrows area. Specifically, only Rb, Ta, Sb, U, Cs, Tb, 

Gd, and Yb are systematically (in two-thirds or more of all 

instances) upward enriched, and only Co, Sr, CaO, and FeO* 

are systematically upward depleted (downward enriched).

The consistency of within-unit behavior for each oxide 

or element was evaluated in a similar manner. Of the 44 samples collected in the compositional profiles, 29 pairs of these 

represent upsection, within-unit transitions. Whether the 

abundance of each oxide or element increases, decreases, or 

is unchanged (within analytical uncertainty) was compiled 

(from table 1) for each of these upsection within-unit sample 

pairs. The difference between the number of enrichments 

and depletions for each oxide or element in each of these 29 

transitions was computed (table 6) and plotted (fig. 19) as a 

histogram in the form of an enrichment-depletion diagram 

that indicates the degree to which abundance variations of 

particular oxides and elements are monotonic. Within-unit 

oxide or element abundance variation is surprisingly nonmonotonic. Specifically, only the abundances of SiO2,
32 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

rubidium, tantalum, and cesium display systematic (in twothirds or more of all instances) within-unit, upsection 

increases, and only the abundances of calcium, cobalt, FeO*, 

and strontium display similarly systematic within-unit, 

upsection decreases.

The representative nature of compositional data for 

samples from the compositional profiles is verified by comparing abundance ranges defined by compositional profile 

sample suites with those portrayed by samples collected 

without regard to vertical position. Specifically, abundance 

ranges for most of the oxides and elements in samples from 

compositional profiles of most of the stratigraphic units generally encompass (within analytical uncertainty) the abundance range defined by samples collected without regard to 

vertical position (fig. 16). Exceptions to this generalization 

probably reflect complex dynamics prevailing during eruption and emplacement. In some cases, as portrayed, for 

instance, by data for samples of the tuff of the Golden Gate 

Range (fig. 16), samples collected without regard to vertical 

position depict compositions that are missing from corresponding composition profile abundance ranges. These 

"missing" compositions, representing tuff aliquots derived 

from the highest and (or) lowest erupted parts of a zoned reservoir, may indicate nonpreservation, due to topographic 

relief or postdepositional scouring, in sections represented 

by corresponding composition profiles. In addition, the distal nature of these outflow deposits enhances the probability 

that some eruptive pulses, potentially representing any level 

within a zoned reservoir, may not have travelled to and been 

deposited in the Narrows area.

DISCUSSION 

CORRELATION

Compositional ranges of major oxides and trace elements in samples of tuffs of the Narrows area (fig. 16) can be 

used to help determine the stratigraphic identity of a unit if 

field, petrographic, paleomagnetic, and geochronologic data 

either are unavailable or are insufficient. By comparing compositional data for a sample of tuff whose stratigraphic identity is uncertain with documented compositional ranges (fig. 

16), it may be possible to identify the unknown tuff. This 

approach would be especially useful where limited exposure 

or structural dismemberment results in limited stratigraphic 

context. Various combinations or subsets of major oxides and 

trace elements, combined with field, petrographic, paleomagnetic, or geochronologic data, may facilitate stratigraphic correlation (Hildreth and Mahood, 1985).

In parts of the Seaman Range, contacts were mapped 

between distinct ash-flow tuffs whose stratigraphic identity 

could not be conclusively established on the basis of field 

observations. In addition, many problems developed during 

attempts by early workers to identify some of the ash-flow

tuffs in the southeastern Great Basin. For instance, although 

Best, Christiansen, and others (1989), Best and others 

(1993), and Scott and others (in press) have summarized the 

petrographic, geochronologic, and paleomagnetic characteristics of the Cottonwood Wash Tuff, Wah Wah Springs 

Formation, Lund Formation, and Monotony Tuff, these units 

are frequently mistaken for one another. These factors led to 

development of the diagnostic compositional attributes for 

correlation described following.

Compositional data for a sample from limited outcrops 

of the Wah Wah Springs Formation in the Narrows area 

provide an inadequate base for stratigraphic correlation 

using geochemical criteria. Elevated MgO, cobalt, nickel, 

chromium, zinc, and scandium abundances in this sample 

relative to all other tuffs in the Narrows area (fig. 16, table 

5) suggest that composition data may be definitive in identification of this unit.

In the Narrows area, in particular, it has been difficult 

to distinguish the Lund from the Monotony in outcrops that 

lack stratigraphic context. Best and Grant (1987) indicated 

that the presence of accessory sphene is diagnostic of the 

Lund, but this criterion is not always reliable because sphene 

breaks down readily during vapor phase recrystallization; 

thus, although present as a magmatic phase, it may be absent 

in recrystallized tuff. Trace-element abundances (table 5) 

indicate, however, that the Lund and Monotony are compositionally distinct. In particular, the Lund has barium abundances distinctly lower than those of the Monotony. Most, 

but not all, "lower" barium samples also contain sphene.

M.G. Best (written commun., 1989) suggested that clinopyroxene is diagnostic of the Monotony. This observation 

was confirmed; no pyroxene was identified during petrographic analysis of 10 samples of compositional Lund rock 

from the Narrows area, whereas all 6 samples of compositional Monotony rock contained clinopyroxene. Although 

the presence of clinopyroxene seems to be diagnostic of 

Monotony, the extremely fine grain size and sparse abundance of this mineral cause this criterion to be of limited utility. Tentative identification of the Lund or Monotony can be 

achieved using the presence of sphene or clinopyroxene, and 

more certain distinctions can be made using relative abundances of barium, TiC>2, PiOs* and thorium (definitive) and 

SiC>2, FeO*, tantalum, and many of the rare earth elements 

(less definitive) in samples of these two units.

The Petroglyph Cliff Ignimbrite shares a number of 

compositional similarities with the Isom-compositional type 

tuffs (Best, Christiansen, and others, 1989). In particular, it 

is characterized by a low SiC>2 content and high abundances 

of FeO*, TiO2, ?2O5, zirconium, scandium, europium, and 

the heavy rare earth elements relative to most other tuffs of 

the Narrows area.

Compositional data for tuffs in the interval between the 

Monotony and the Leach Canyon Formation in the Narrows 

area provide a clear example of the utility of compositional 

data, and of trace elements in particular, in stratigraphic
DISCUSSION 33

v v V V V V V V V

400 -

100 300 500 700 

STRONTIUM, IN PARTS PER MILLION

SR

A

RB

RB

B

SR

Figure 20. Variation diagrams showing compositions of samples of in the stratigraphic interval between (and including) the Baldhills and 

Hole-in-the Wall Members of the Isom Formation, White River Narrows area, Nevada. BH, Baldhills Member of the Isom Formation; SPL 

and SPI, lower and intermediate cooling units, respectively, of the Shingle Pass Tuff; GG, tuff of the Golden Gate Range; HS, tuff of Hancock 

Summit; SPU, upper cooling unit of the Shingle Pass Tuff; HW, Hole-in-the-Wall Member of the Isom Formation. A, Strontium-zirconiumrubidium. Data for the upper cooling unit of the Shingle Pass Tuff shown by pluses. B, Rubidium-barium-strontium. Data for the Hole-inthe-Wall Member of the Isom Formation shown by pluses. C, Barium versus strontium. Data for the Hole-in-the Wall Member of the Isom 

Formation shown by pluses.

correlation. At the onset of geologic mapping in the Seaman 

Range (du Bray and Hurtubise, 1994), ash-flow tuff stratigraphy in the interval between the Monotony Tuff and the 

Leach Canyon Formation was poorly known. Field observations indicated that a number of grossly similar tuffs were

present within this interval but that their distribution was not 

continuous throughout the Seaman Range. Trace-element 

data for samples collected without regard to vertical position 

within this interval suggested the presence of seven compositionally distinct stratigraphic units (fig. 20). Subsequent
34 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

work demonstrated that the abundances of rubidium, strontium, zirconium, and barium in each of these units define distinct, generally nonoverlapping compositional fields (fig. 

20). Units whose compositional fields overlap on one diagram, such as those of the tuff of the Golden Gate Range and 

the upper cooling unit of the Shingle Pass Tuff on the ternary 

strontium-zirconium-rubidium diagram (fig. 20A), form distinct fields on a barium versus strontium plot (fig. 20C). Noting relative stratigraphic and geographic positions of 

samples that composed the various compositional groups 

enabled development of a composite stratigraphic column 

containing these seven ash-flow tuffs. Ultimately, an intact 

section, 1.5 km north of Fossil Peak (fig. 1), containing all of 

these tuffs, in stratigraphic contact, was identified and sampled in detail to verify the inferred relative stratigraphic and 

compositional relations.

Compositional data for the Leach Canyon Formation 

provide another example of the utility of trace-element data 

in stratigraphic correlation. Multiple ash flows were 

observed within the Leach Canyon Formation; analytical 

data for samples from throughout this unit enable identification of a major compositional, stratigraphic break within this 

sequence of ash flows. The composition break is coincident 

with the prominent horizontal parting noted by Williams 

(1967) within the Narrows Tuff Member of the Leach Canyon Formation in the Narrows area (fig. 1). Ash-flow tuff in 

the lower part of the Leach Canyon Formation is characterized by elevated abundances of SiO?, Ta, Th, and U and by 

depleted abundances of FeO*, P2Os, Sr, Ba, Zn, Sc, and the 

light rare earth elements relative to their abundances in tuff 

from the upper part of the Leach Canyon Formation and other 

tuffs of the Narrows area (fig. 16). Abundances of individual 

trace elements in samples of the upper ash-flow tuff of the 

Leach Canyon Formation are not diagnostic although combinations of trace-element features, such as low zirconium, 

scandium, and rare earth element abundances and elevated 

Na2O, cobalt, and tantalum abundances, enable discrimination of this unit from other tuffs of the Narrows area.

The composition of the S wett Tuff Member of the Condor Canyon Formation is distinguished by abundances similar to those of the Isom-compositional-type tuffs of Best, 

Christiansen, and others (1989). Specifically, samples of the 

Swett Tuff Member are characterized by elevated abundances of K2O, Zr, Hf, La, Ce, Tb, Yb, and Lu. These compositional features, as well as previously described 

distinctive field appearance, thinness, and petrographic characteristics, clearly distinguish the Swett Tuff Member from 

other tuffs of the Narrows area.

One of the most diagnostic features of the Bauers Tuff 

Member of the Condor Canyon Formation is its relative 

compositional homogeneity. In addition, samples of the 

Bauers Tuff Member are characterized by elevated abundances of Na2O, K2O, zirconium, and hafnium and among 

the highest abundances of thorium and uranium of any of 

tuffs of the Narrows area.

The Pahranagat Formation is one of the most silica rich 

tuffs of the Narrows area. Another diagnostic feature of the 

Pahranagat is its relatively weakly developed incompatible 

trace-element enrichment for such a high-silica rhyolite. It is 

further distinguished by low abundances of FeO*, strontium, 

zirconium, barium, scandium, and light rare earth elements. 

These compositional characteristics and abundant unflattened pumice blocks are diagnostic of this unit.

The Harmony Hills Tuff is the most mafic of the Narrows area tuffs. Its composition is characterized by low 

SiO2 abundances and by high abundances of FeO*, MgO, 

CaO, TiO2, P2C<5, strontium and particularly high abundances of cobalt, nickel, chromium, and scandium relative 

to the other tuffs of the Narrows area. Relatively coarse, 

abundant biotite also distinguishes this unit from other 

tuffs of the Narrows area.

The composition of the Hiko Tuff is perhaps the most 

nondistinct of any tuff exposed in the Narrows area. Abundances of most oxides and elements in samples of this unit 

overlap those of many other tuffs of the Narrows area. The 

Hiko Tuff is characterized by slightly low abundances of 

yttrium relative to most of tuffs of the Narrows area and by 

high abundances of cobalt relative to all of tuffs of the Narrows area younger than the Monotony Tuff. Fortunately, its 

stratigraphic position above the distinctive Harmony Hills 

Tuff and the fact that it weathers to prominent low cliffs covered by a distinctive moderate-reddish-brown patina render 

it somewhat distinctive.

ZONATION

Most of tuffs of the Narrows area display compositional 

zoning that is generally similar to that described for the 

Bishop Tuff (Hildreth, 1979); however, compositional zonation within the tuffs of the Narrows area is less systematic 

than that of some high-silica rhyolites and the magnitude of 

enrichments and depletions is smaller (fig. 18). Specifically, 

the most systematically zoned of the tuffs of the Narrows 

area—that is, tuffs whose compositions most nearly display 

monotonic variation in their composition profiles—are the 

Petroglyph Cliff Ignimbrite, the Swett Tuff Member of the 

Condor Canyon Formation, and the upper part of the Leach 

Canyon Formation (fig. 16). The tuff of the Golden Gate 

Range, the Petroglyph Cliff Ignimbrite, the Swett Tuff Member, and the Pahranagat Formation are among the most 

strongly zoned of tuffs of the Narrows area (fig. 17), whereas 

the Harmony Hills Tuff, the Bauers Tuff Member of the 

Condor Canyon Formation, the upper part of the Leach Canyon Formation, and lower and upper cooling units of the 

Shingle Pass Tuff are the most weakly zoned.

Relative to the Bishop Tuff, the Monotony Tuff is 

reversely zoned in many elements. Abundances of SiO2, 

K2O, rubidium, barium, thorium, uranium, and light rare 

earth elements are enriched in samples (inferred to represent
CONCLUDING REMARKS 35

deep reservoir levels) from the top of the Monotony composition profile, whereas abundances of FeO, MgO, CaO, 

TiO2, strontium, and scandium are enriched in samples 

(inferred to represent shallow reservoir levels) from the base 

of the profile (table 2, fig. 16).

One explanation for the reversed zoning is that the 

Monotony Tuff source reservoir was normally zoned and 

was evacuated from bottom to top. This scenario is unlikely, 

however, because it would require very high initial eruption 

rates (Blake and Ivey, 1986a, b), followed by progressively 

decreasing eruption rates. This eruption style requires that 

magma in the upper part of the reservoir be effectively shouldered aside and blocked from entering eruption conduits by 

magma surging upward, from deep in the reservoir, in 

response to very high eruption rates; this process requires a 

large vent and an enhanced eruption driving force.

A second possibility is that the contents of the Monotony Tuff reservoir became reversely zoned by magmatic 

processes. Zonation of this type, however, has not been demonstrated for other systems, and the mechanisms by which 

this type of zonation would develop are unknown.

Another process by which the Monotony Tuff might 

have become reversely zoned is that outlined by Duffield 

and Ruiz (1992) for the reversely zoned part of the Oligocene Taylor Creek Rhyolite reservoir. They suggested that 

magmatic processes within the reservoir favored normal 

zonation but that these processes were overwhelmed, specifically at the top of the reservoir, by assimilation of relatively 

geochemically primitive roof rock that caused compositional 

zonation reversal. Similarly, assimilation of relatively unevolved roof rocks at the top of the Monotony reservoir may 

have overwhelmed evolution of a normal composition profile. If so, progressively more evolved compositions from 

deeper in the chamber (stratigraphically higher samples) 

would indicate decreasing contamination by assimilation of 

geochemically primitive roof rock.

The composition of sample 201723 from the top of the 

Monotony profile (inferred to represent the deepest sampled 

level in the source reservoir) depicts a zonation reversal 

toward normal zonation and more primitive compositions. 

This observation suggests the presence of a threshold in the 

Monotony reservoir, in the part of the reservoir represented 

by samples 201723 and 201722, in which magmatic processes that lead to normal zonation became dominant over 

the roof-rock assimilation or contamination process.

Compositions of the uppermost samples of the Lund 

and Pahranagat Formations reverse the variation patterns 

portrayed by the remaining samples in these profiles (fig. 

16). In each unit, uppermost samples depict more evolved 

compositions than the samples collected immediately below. 

Thus, these samples represent a discontinuity in the pattern 

of eruption of progressively less evolved magma from progressively deeper reservoir levels. These compositional relations may depict diminished eruption rates during the 

waning stages of reservoir evacuation. As a consequence,

more evolved, residual magma, shouldered aside and 

blocked from eruption conduits during the time of high eruption rates, was able to reestablish contact with eruption conduits. Pertinent studies concerning the effects of variable 

eruption dynamics have been discussed by Blake and Ivey 

(1986a, b), and similar compositional reversals, described by 

Boden (1989), characterize ash-flow tuff erupted from the 

Toquima caldera complex of Nevada.

CONCLUDING REMARKS

Trace-element data enabled conclusive identification 

and correlation of middle Tertiary ash-flow tuffs in the Narrows area of the southeastern Great Basin. Whole-rock 

analysis by energy-dispersive X-ray fluorescence is fast and 

relatively inexpensive; thus, use of this type of data should 

become a more routine part of ash-flow tuff characterization and correlation.

Hildreth (1979, p. 71) urged that "Elemental distribution patterns within several well-preserved ash-flow complexes that cover a range of volumes, compositions***need 

to be established." Middle Tertiary ash-flow tuffs of the 

southeastern Great Basin, especially those of the Narrows 

area, meet these criteria well. Some speculation concerning 

the differences between vertical compositional zonation in 

high-silica ash-flow tuffs, as epitomized by the Bishop Tuff, 

and tuffs of the Narrows area follows.

The bulk composition of magma erupted during 

caldera-forming events is certainly a function of conditions 

prevailing in the source region during magma genesis and is 

also a function of pre-eruption reservoir processes. Highly 

evolved high-silica magmas, which are characterized by 

extreme geochemical gradients, may require significantly 

more time to evolve in crastal reservoirs than less evolved, 

less strongly zoned systems. The diversity of vertical zonation portrayed by tuffs of the Narrows area may, in part, 

reflect pre-eruption reservoir residence times.

Perhaps the most characteristic feature of high-silica 

tuffs is their extremely evolved geochemical character. The 

compositions of these tuffs depict maximum degrees of 

geochemical evolution including remarkable enrichments in 

Rb, Nb, Y, Sb, Cs, Ta, U, and heavy rare earth element 

abundances and depletions in FeO*, Ba, Sr, and Eu abundances. None of tuffs of the Narrows area is characterized 

by geochemical features of this type; herein may lie a 

source of the differences in the consistency and magnitude 

of enrichments and depletions in oxide-element abundances 

for tuffs of the Narrows area.

The similar sense and magnitude of enrichment and 

depletion in high-silica systems for most reservoirs (Hildreth, 1979) suggest that similar geochemical processes are 

acting with similar efficiencies in these systems. Processes 

such as double-diffusive fractional crystallization (Christiansen, 1983) that result in extreme compositional gradients
36 OLIGOCENE AND MIOCENE ASH-FLOW TUFFS, NEVADA

in high-silica reservoirs may operate weakly, if at all, in less 

evolved reservoirs. Variability of the sense and magnitude of 

enrichments and depletions portrayed by tuffs of the Narrows area suggests that no single process can be responsible 

for evolution of these geochemical features. Because reservoirs represented by tuffs of the Narrows area were not similarly zoned, other processes, in particular crystal 

fractionation, were more likely responsible for geochemical 

gradients preserved in composition profiles of tuffs of the 

Narrows area.

Tuffs of the Narrows area span a wide composition 

range, from low-silica dacite to high-silica rhyolite. Consequently, geochemical processes and efficiencies controlling 

the development of vertical zonation in their source reservoirs may have been highly variable. In particular, if crystalliquid equilibrium and crystal fractionation played major 

roles in compositional evolution, the fact that magma bulk 

compositions, as indicated by the diversity of average compositions of ash-flow tuffs of the Narrows area, were different among the stratigraphic units mandates distinct 

fractionating mineral assemblages for each of the source reservoirs. Variable fractionating assemblages, each having distinctive bulk distribution coefficients, may have caused the 

sense and magnitude of oxide or element enrichments and 

depletions defined by tuffs of the Narrows area to be highly 

variable. Rigorous petrogenetic modelling is beyond the 

scope of this study, but data presented herein pertaining to 

compositions of the tuffs of the Narrows area and to the type 

and relative proportions of phenocrysts contained therein 

should prove useful in future studies of compositional evolution within individual middle Tertiary magma reservoirs of 

the southeastern Great Basin.

The temporal-compositional variation among Narrows 

area tuffs, known to have been derived from several sources, 

may provide some insight, though highly speculative, into 

the crust-mantle magmatic processes responsible for voluminous middle Tertiary magmatism in the southeastern Great 

Basin. In particular, with regard to Cenozoic magmatism in 

the southeastern Great Basin, it is noteworthy that Johnson 

(1991) considered that all Cenozoic silicic ash-flow magma 

in western North America results from fractional crystallization of mantle-derived magmas that assimilated varying 

amounts of continental crust.

One of the initial, voluminous pulses of middle Tertiary 

magmatism in the southeastern Great Basin, represented by 

the eruption of voluminous dacitic ash flows from the Indian 

Peak caldera complex, may reflect input of mantle-derived 

basaltic magma at the base of the crust and its evolution by 

fractional crystallization and assimilation to dacitic compositions. This influx of basaltic magma at the base of the crust 

probably caused anatexis throughout the region and generation of relatively low density liquids whose presence created 

a gravitational boundary to further upward migration of 

more dense basaltic magma. The resulting anatectic magmas 

may be represented, as a consequence of similar processes

acting throughout a large region, by ash-flow tuffs erupted 

from the Central Nevada and Caliente caldera complexes. 

The compositions of these ash-flow tuffs are dramatically 

more evolved (fig. 16) than those of the Indian Peak caldera 

complex, perhaps because they represent eruption of magma 

generated by partial melting at the base of the crust and 

therefore include smaller mantle components than more 

nearly primary magmas erupted from the Indian Peak 

caldera complex. This hypothesis could be tested using 

radiogenic isotopic data.

The eruption of progressively less evolved magmas 

from the Central Nevada and Caliente caldera complexes 

(fig. 16) may reflect the emptying (by eruption) and solidification of the anatectic reservoirs. Residual magma in 

these reservoirs may have involved progressively larger 

mantle components as the low-density barrier above basalt 

ponded at the base of the crust was eliminated; subsequently erupted magma, which may have included progressively larger mantle contributions, was geochemically less 

evolved as a consequence. This process culminated, as ashflow eruptions diminshed during the early Miocene, with 

the renewed eruption, beginning about 17 Ma (Best, Christiansen, and others, 1989), of mantle-derived basalt in the 

southeastern Great Basin.

REFERENCES CITED

Anders, Edward, and Ebihara, Mitsuru, 1982, Solar-system abundances of the elements: Geochimica et Cosmochimica Acta, 

v. 46, p. 2363-2380.

Anderson, J.J., and Rowley, P.O., 1975, Cenozoic stratigraphy of 

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Published in the Central Region, Denver, Colorado

Manuscript approved for publication August 16, 1994

Edited by Judith Stoeser

Graphics prepared by Denny Welp, Alex Donatich, and the author

Photocomposition by Mari L. Kauffmann

Tables typeset by Judith Stoeser

.S. GOVERNMENT PRINTING OFFICE: 1995-673-046/86077
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