Summary of Chemical Analyses and 

40Ar/39Ar Age-Spectra Data for 

Eocene Volcanic Rocks from the 

Central Part of the 

Northeast Nevada Volcanic Field

U.S. GEOLOGICAL SURVEY BULLETIN 1988-K

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Summary of Chemical Analyses and 

40Ar/39Ar Age-Spectra Data for 

Eocene Volcanic Rocks from the 

Central Part of the 

Northeast Nevada Volcanic Field

By William E. Brooks, Charles H. Thorman, Lawrence W. Snee, 

Constance J. Nutt, Christopher J. Potter, and Russell F. Dubiel

EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN 

Harry E. Cook and Christopher J. Potter, Project Coordinators

U.S. GEOLOGICAL SURVEY BULLETIN 1988-K

A multidisciplinary approach to research studies of sedimentary 

rocks and their constituents and the evolution of 

sedimentary basins, both ancient and modern

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

Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks 

from the central part of the Northeast Nevada volcanic field / by William E. 

Brooks... [et al.].

p. cm. (Evolution of sedimentary basins Eastern Great Basin ; K) 

(U.S. Geological Survey bulletin ; 1988)

Includes bibliographical references.

Supt.ofDocs.no.: I 19.13 : B1988-K

1. Rocks, Igneous Nevada Composition. 2. Argon-argon dating Nevada. 

3. Geochemistry Nevada. 4. Geology, Stratigraphic Eocene. I. Brooks, 

William E. II. Series. III. Series : Evolution of sedimentary basins Eastern 

Great Basin ; ch. K. 

QE75.B9 no. 1988-K 

[QE461] 

557 s dc20

[552'.2' 09793] 95-23828

CIP
CONTENTS

Abstract........................................................................................................................... Kl

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

Regional Eocene Setting................................................................................................. 1

Data Tables and Plots of Analyses.................................................................................. 5

References Cited............................................................................................................. 31

FIGURES

1. Map showing central part of Northeast Nevada volcanic field, composite stratigraphic column for Nanny

Creek type area, and schematic west-east cross section of central part of Northeast Nevada volcanic field.............. K2

2. Age-spectrum diagrams for volcanic rocks from the central part of the Northeast Nevada volcanic field................. 4

3. Geologic map of the Nanny Creek area, northern Pequop Mountains, Nevada.......................................................... 6

4. AFM ([Na2O+K2O]-FeO-MgO) diagrams for samples from the central part of the

Northeast Nevada volcanic field.................................................................................................................................. 7

5. Total-alkali (Na2O-t-K2O)-(SiO2) diagrams for samples from the central part of the

Northeast Nevada volcanic field.................................................................................................................................. 7

6. Total-alkali (Na2O+K2O)-(SiO2) diagrams for samples from the central part of the

Northeast Nevada volcanic field by locality................................................................................................................ 8

TABLES

1. Regional summary of localities at which Eocene volcanic rocks have been dated, northeast Nevada

and adjacent Utah......................................................................_ K9

2. Chemical analyses of Eocene volcanic rocks from the Nanny Creek type area, Northeast Nevada

volcanic field......................................................................._ 10

3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada

volcanic fi&d................................................................................................................................................^ 13

4. Summary of 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the

Northeast Nevada volcanic field................................................................................................................................. 22

5. Abbreviated 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the

Northeast Nevada volcanic field.................................................................................................................................. 23

6. Production ratios for interfering isotopes of argon produced during irradiation......................................................... 30

7. U-Th-Pb isotopic ages of sphene from pyroxene diorite, southern East Humboldt Range,

central part of Northeast Nevada volcanic field.......................................................................................................... 31

ffl

Summary of Chemical Analyses and

40Ar/ 39Ar Age-Spectra Data for

Eocene Volcanic Rocks from the

Central Part of the Northeast Nevada Volcanic Field

By William E. Brooks, Charles H. Thorman, Lawrence W. Snee, 

Constance J. Nutt, Christopher J. Potter, and Russell F. Dubiel

ABSTRACT

Widespread rhyolitic to andesitic calc-alkaline 

volcanic rocks in northeast Nevada and northwest Utah are 

part of a distinct Eocene eruptive sequence that is older than 

previously believed. Parts of this volcanic terrane, the 

central part of the Northeast Nevada volcanic field, are 

exposed over a large area that extends in an east-west 

direction from the Silver Island Mountains, Utah, to Elko, 

Nevada, and in a north-south direction from an area a few 

miles north of Wells, Nevada, to the Deep Creek Range, 

Utah.

The type area for the Northeast Nevada volcanic field 

is at Nanny Creek, in the northern Pequop Mountains, where 

the base of the volcanic sequence, unconformable on 

Eocene lacustrine deposits, includes rhyolitic ash-flow tuffs 

that are overlain by a monotonous series of dacitic to 

andesitic flows and flow breccias that were locally erupted. 

The similarities in age, chemistry, and mode of occurrence 

of these volcanic rocks throughout the field indicate that 

they are part of the same widespread Eocene volcanic 

sequence.

INTRODUCTION

Middle to late Eocene calc-alkalic volcanism that 

formed the Northeast Nevada volcanic field marks the onset 

of Tertiary volcanism in the northern Basin and Range. The 

central part of this large field, in northeast Nevada and adjacent Utah, is defined by (1) 12 numbered localities (fig. I A) 

from which 23 40Ar/39Ar ages, ranging from 42.6 to 39.0 

Ma, were obtained, (2) more than 90 chemical analyses, (3) 

stratigraphic position of the volcanic rocks above a regional 

Eocene unconformity, and (4) lithology. The type area is at

Nanny Creek in the northern Pequop Mountains, Nevada 

(Brooks and others, 1992, 1995a, b; Thorman and others, 

1993) (fig. 1). Prior to our studies, dated middle Eocene volcanic rocks were known at a only few widespread sites in 

northeast Nevada and adjacent Utah (fig. IA, lettered localities; table 1). Integration of ages (K-Ar method) from these 

localities into a regional volcanic framework was difficult 

because (1) the localities are geographically scattered and 

(2) only a few chemical analyses of these dated volcanic 

rocks are available.

On the basis of the previously sampled localities having middle Eocene ages listed in table 1, the Northeast 

Nevada volcanic field was defined as extending east to the 

Cottonwood Canyon area in the Wasatch Range, Utah, north 

to the Nevada-Idaho State line, south to the Roberts Mountains in central Nevada and west to the Snowstorm Mountains in north-central Nevada. Sparse chemical analyses and 

no 40Ar/39Ar dates are available for Eocene volcanic rocks 

at localities listed in table 1. As part of an ongoing regional 

study, samples of the volcanic rocks from those localities in 

table 1 were recollected for chemical and geochronological 

(40Ar/39Ar method) analysis in order to help delineate the 

regional extent of the Northeast Nevada volcanic field.

REGIONAL EOCENE SETTING

The Northeast Nevada volcanic field consists of the 

coalesced products of intermediate to rhyolitic, calk-alkalic 

volcanism in northeast Nevada and adjacent Utah that were 

erupted from 42.6 to 39 Ma, during Eocene time. The central 

part of the Northeast Nevada volcanic field (Brooks and 

others, 1995) was defined by mapping and stratigraphy at 12 

localities (fig. LA), by 92 major oxide chemical analyses of

Kl
K2 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

40'

Figure 1 (above and facing page). Map showing central part of 

Northeast Nevada volcanic field, northeast Nevada and adjacent 

Utah, composite stratigraphic column for Nanny Creek type area, 

and schematic west-east cross section of central part of Northeast 

Nevada volcanic field. A, Map showing localities (solid circles) 

from which Eocene volcanic rocks were dated and analyzed. Shaded areas indicate ranges. Samples from numbered localities were 

collected as part of this study: 1, Nanny Creek, northern Pequop 

Mountains; 2, southern Snake Mountains; 3, northern East 

Humboldt Range; 4, southern East Humboldt Range; 5, Deadman 

Creek area, Windermere Hills (Mueller, 1992); 6, Wood Hills; 7, 

Ferguson Mountain (J. Welsh, U.S. Geological Survey, unpub. 

mapping, 1992); 8, Dolly Varden Mountains (Zamudio, 1992); 9, 

Silver Island Mountains; 10, Sanford Springs, southern Deep Creek 

Mountains; 11, Gold Hill area, northern Deep Creek Mountains 

(Dubiel and others, 1993); 12, Coal Mine Canyon, northern Adobe 

Range, east side of Elko Basin (K. Ketner, U.S. Geological Survey, 

written commun., 1993). Letters indicate localities of Eocene 

volcanic rocks previously studied: a, central Pilot Range, Utah, 

K-Ar (biotite), 37.1 Ma, tuff and sedimentary rock, (Miller, 1984); 

b, central Pilot Range, Utah, K-Ar (biotite), 36.9 Ma, tuff, (Miller,

1984); c, Silver Island Mountains, Utah, K-Ar (biotite), 40.9 Ma, 

andesite (Moore and McKee, 1983); d, Gold Hill, Utah, K-Ar 

(biotite), 39.2 Ma, latite (Moore and McKee, 1983); e, Grouse 

Creek Mountains, Utah, K-Ar (biotite), 36.4 Ma, tuff (Compton, 

1983); f, Tuscarora (Big Cottonwood Canyon caldera), Nevada, 

K-Ar (biotite), 40.5 Ma, tuff (B.R. Berger, U.S. Geological Survey, 

written commun., 1993); g, Tuscarora, Nevada, K-Ar (biotite), 41.9 

Ma, basal ash-flow tuff (Boden and others, 1993); h, Tippett 

Canyon, southern Deep Creek Mountains, Nevada, 40Ar/39Ar 

(biotite), 39.5 Ma, tuff (Gans and others, 1989); i, Independence 

Range, Nevada, 40Ar/39Ar (biotite), 41.6 Ma, tuff (A.H. Hofstra, 

U.S. Geological Survey, written commun., 1994). B, Composite 

stratigraphic column, Nanny Creek type area. Ages were 

determined by Ar/3 Ar method; solid circles indicates dated 

units. Map units T1, T2, T3, and T4 are shown in figure 3. C, Schematic west-east cross section of the central part of the Northeast 

Nevada volcamc field. Intertonguing relationship of lava flows and 

pre-Eocene and early to middle Eocene unconformities (heavy 

dashed and solid lines, respectively) are generalized. Lines in 

sedimentary units in the Elko Basin and the White Sage Basin indicate tilted, bedded units, not true dip. No vertical scale implied.
NORTHEAST NEVADA VOLCANIC FIELD K3

Eroded top

Hornblende rhyolite (T4)

Intercalated unit (T3)

Crystal-poor ash-flow tuff (T2)

Crystal-rich ash-flow tuff (T1) 

Basal conglomerate

WEST

ELKO BASIN NANNY CREEK

EAST

WHITE SAGE 

BASIN

volcanic rocks and 1 analysis of a coeval pyroxene diorite 

(tables 2, 3), and by 23 40Ar/39Ar ages (table 4) from 12 

localities. Age-spectrum diagrams and abbreviated data 

tables for samples from the 12 numbered localities shown in 

figure IA are presented in figure 2 and table 5, respectively. 

Production ratios are presented in table 6. Comparable 

volcanic setting, lithology, and stratigraphic position of the 

volcanic rocks above a regional middle Eocene unconformity (Thorman and Brooks, 1991) that is recognized in the 

Elko Basin (Wingate, 1983; Ketner and Ross, 1990) to the 

west and in the White Sage Basin to the east (Potter and 

others, 1995) (figs. 1A, Q are also significant in the regional 

reconstruction of this Eocene volcanic terrane.

The Northeast Nevada volcanic field coincides in time 

and space with the Tuscarora magmatic belt of Christiansen 

and Yeats (1992), which was broadly defined using only a 

few K-Ar ages and no rock chemistry. The type area for the 

Northeast Nevada volcanic field is at Nanny Creek (fig. 15, 

loc. 1, fig. 3) in the northern Pequop Mountains, where the 

section is 1,200 m thick. Here, rhyolite ash-flow tuffs (units 

T1, T2) are overlain by a thick section of intercalated andesitic to dacitic flows and flow breccias (unit T3x) and rhyolite 

ash-flow tuffs (unit T3a). These rocks, which are dated, are 

overlain by an undated hornblende rhyolite, and regional 

relationships of the flows, flow breccias, tuffs, and underlying Paleozoic strata are shown schematically in figure 1C. A 

widespread basal sedimentary unit is included in the stratigraphic section because of the tectonic implications of 

included Eocene volcanic material (Brooks and others, 

1995). Typically, the volcanic outcrops of the field are 

widely scattered, have limited areal extent, and are discontinuous between ranges.

Intermediate-composition volcanic rocks, including 

hornblende andesite, two-pyroxene andesite, and biotite 

(±hornblende) dacite, probably were locally derived from 

numerous vents throughout the field, whereas calderas for 

the biotite (±hornblende, quartz, lithic) rhyolite ash-flow 

tuffs are, for the most part, unknown. For example, in the

Folded and faulted 

Paleozoic and Mesozoic strata

EXPLANATION

EOCENE ROCKS OF 

NORTHEAST NEVADA VOLCANIC FIELD

Intermediate-composition flows 

and breccias

Ash-flow tuff 

Rhyolite flow 

Conglomerate

ELKO AND WHITE SAGE FORMATIONS (EOCENE) 

Lacustrine ostracode-bearing limestone

Subhorizontal

Tilted

Fault

southern East Humboldt Range (fig. 1A, loc. 4) several 

volcanic centers in andesitic to dacitic rocks are characterized by flows, scoriaceous agglomerate, spatter, and 

near-source, oxidized, angular block and breccia (2-3 m) 

flows, all of which are features present in low hills with 

shieldlike morphology. A hypabyssal center in the southern 

East Humboldt Range was identified on the basis of an 

Eocene (U-Th-Pb ages of 39.5±0.4 Ma and 37.8±0.3 Ma on 

two sphene fractions; R.E. Zartman, USGS, written commun., 1994) pyroxene diorite (table 3, sample 91T22; table 

7) that intruded and contact metamorphosed the Permian and 

Triassic strata. This fine-grained holocrystalline rock 

weathers much the same as its nearby extrusive equivalents 

and can be easily mistaken for andesite. In the southern Deep 

Creek Range, near Sanford Springs, a dissected 

block-and-cinder cone 40 m high is exposed through dacitic 

to andesitic flows and flow breccias (Nutt and Brooks, 

1994).
K4 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

NANNY CREEK NORTHERN EAST HUMBOLDT RANGE

APPARENT (Ma) AGE 

40

30 

40

30

30

20 

40

30 

or\

| 1 1 1 1 1 1 1 1 1

NU 91 T1 0 (hornblende) 39.23 ± 0.5 Ma

H 90B9B (biotite) 39.61 ± 0. 1 3 Ma

88T55 (biotite) 39.89 ±0.1 2 Ma

88T56 (biotite) 41.08 ±0.11 Ma ~~

I I I I I I I I I

0 10 20 30 40 50 60 70 80 90 100 

PERCENT 39Ar RELEASED

K

SOUTHERN SNAKE MOUNTAINS

CO

kRENTAGE(

D. 

0-

40

30 

40

30

20 

40

30

20 

40

30

20

_lll II I ^

J 88T36 (biotite) 39.5 ± 0.2 Ma

f^ 88T42 (biotite) 39,7 ± 0.1 Ma

T

f J

J 88T41 (biotite) 39. 76 ±0.1 3 Ma

J ~~

88T38 (biotite) 39.85 ± 0.15 Ma

-

-Ill II

0 10 20 30 40 50 60 70 80 90 100 

PERCENT 39Ar RELEASED

K

LU 40

8

LU 30

90B31B (biotite) 38.0 ± 0.5 Ma

0 10 20 30 40 50 60 70 80 90 100 

PERCENT 39Ar, RELEASED l\

SOUTHERN EAST HUMBOLDT RANGE

50

40

30

20

50

i r

Lr 91T12 (hornblende) 38.8 ± 0.4 Ma

LU

40

Q. 

Q_

30

91T17 (hornblende) 39.5 ± 0.3 Ma

20

91T19 (biotite) 40.98 ± 0.1 Ma

0 10 20 30 40 50 60 70 80 90 100 

PERCENT 39ArK RELEASED

WOOD HILLS

LU

<2 40

<

I 

Z 

LUI 30

^ I I I I I I I I I

92BWH1

I I I I I

(biotite) 39.7 ±0.1 Ma

I I

0-0 10 20 30 40 50 60 70 80 90 10

PERCENT 39Ar RELEASED K

FERGUSON MOUNTAIN

APPARENT AGE S8 

1 1 1 1 1 1 1 1 =r j =i ' 

Rn 12659-92T21

II I I I I I

) 10 20 30 40 50 

PERCENT 39Ar

K

(hornblende) 39.8 ±0.1 f

I I I

,1a

60 70 80 90 10 

RELEASED

Figure 2 (above and facing page). Age-spectrum diagrams for volcanic rocks from the central part of the Northeast Nevada volcanic 

field. Sample localities are shown in figure L4. Age-spectrum diagrams for Deadman Creek are given in Mueller (1992)
NORTHEAST NEVADA VOLCANIC FIELD K5

DOLLY VARDEN MOUNTAINS

LU 

O

h- 40

LU 

CC

n C 

CL

1 1 1 1 1 1 1 1 1 

__! 3233-92BDV (biotite) 39.08 ±0.11 Ma _

I I I I I I I I I

10 20 30 40 50 60 70 80 90 

PERCENT 39Ar, RELEASED K

10

SILVER ISLAND MOUNTAINS

APPARENT AG (Ma 

S8 fe3

III 1 1 1 1 i I 1 1 

fl

- H^ bt

r:

91T3 (hornblende) 42.6 ± 0.3 Ma 

H

91T4 (biotite) 42.61 ± 0.08 Ma 

I I I I I I I

0 10 20 30 40 50 60 70 80 90 100

PERCENT 39Ar RELEASED

SANFORD SPRINGS

LU 

O 

< 40

1- 

Z 

LU 

CC 

<r rvi

1 1 1 1

92B27 (biotite) 40.64 ± 0.07 Ma

1 1

0 10 20 30 40 50 60 70 80 90 100

PERCENT 39Ar RELEASED

GOLD HILL

40

LU 30 

O

40

30

91CP33 (biotite) 39.58 ± 0.1 Ma

91CP30 (hornblende) 39.6 ± 0.2 Ma

0 10 20 30 40 50 60 70 80 90 100 

PERCENT 39Ar- RELEASED

COAL MINE CANYON

50

40

12624 (hornblende) 40.4 ± 0.2 Ma

0 10 20 30 40 50 60 70 80 90 100 

PERCENT 39Ar RELEASED

A possible source for some of the rhyolite ash-flow 

tuffs is an Eocene caldera complex near Tuscarora, northwest of Elko (McKee and Coats, 1975; Berger and others, 

1991; Boden and others, 1993). A K-Ar age of 40.5 Ma was 

obtained from vitrophyre at the Big Cottonwood Canyon 

caldera (B.R. Berger, written commun., 1993) in the 

complex.

DATA TABLES AND PLOTS OF 

ANALYSES

Samples of the volcanic units from the numbered 

localities shown in figure 1A were collected in order to 

define regional and local chemical affinity and refine field 

nomenclature. Although most samples are devitrified and 

some are altered, samples were collected and analyzed in 

order to provide analytical data for each locality. 

Potassium-metasomatized volcanic rocks, which have been 

considered absent or sparse in the northern Basin and Range 

(Glazner and Bartley, 1990), are present in the Grant Range 

(Scott, 1965; Brooks and others, 1994), at Round Mountain 

(Shawe and Leprey, 1985), and, by this study, in the southern 

Snake Mountains (table 3, samples 88T36, 88T38, 88T41, 

and 88T42), southern East Humboldt Range (table 3, sample 

92B46), and Deadman Creek area (table 3, sample 90-14). 

This type of alteration, which is usually not obvious in hand 

sample, is indicated by analytical results including minimal 

amounts of Na2O (<1.0 weight percent) and excessive 

amounts of K2O (as much as 12-13 weight percent) that 

yield K2O:Na2O ratios greater than 2 (Brooks, 1986). 

Neither leucite, analcite, nor nepheline, possible host phases 

for the excess potassium in some high-potassium volcanic 

rocks, is present.

Armstrong (1970) recognized problems in dating 

potassium-metasomatized rocks and indicated that dates 

from these altered rocks may indicate the age of 

metasomatism, not the age of the volcanic rock. Biotite from 

metasomatized volcanic rock from the southern Snake 

Mountains was dated by 40Ar/39Ar methods, and those ages 

(table 4) are considered reliable, based on work by Brooks 

and others (1994) on biotite from similarly potassium-metasomatized volcanic rocks in the Grant Range, Nevada. 

Despite their anomalously high potassium content these 

altered rocks are referred to as andesite or dacite because 

their SiO2 content, a key oxide in chemical rock nomenclature, and other major-element contents were little changed 

during metasomatism (Sawyer and others, 1989; Brooks and 

others, 1994). Because of their excessive K2O content, however, analyses from these potassium-metasomatized rocks 

commonly plot in the trachyandesite or trachydacite field on 

a total alkali-silica (TAS) diagram.
K6 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

114°32'3D"

/ PHOTO

' LINEAMENTS
NORTHEAST NEVADA VOLCANIC FIELD K7

Qal

EXPLANATION

Alluvium (Quaternary) 

Hornblende rhyolite (middle Eocene) 

Rhyolite ash-flow tuff (middle Eocene) 

Andesite ash-flow breccia (middle Eocene) 

Crystal-poor rhyolite ash-flow tuff (middle Eocene) 

Crystal-rich rhyolite ash-flow tuff (middle Eocene) 

Conglomerate (middle Eocene) 

Pequop Formation of Steele (1960) (Permian) 

Ely Limestone (Pennsylvanian)

PMdp:j Diamond Peak Formation (Pennsylvanian and Mississippian) 

Mch ~~ Chainman Formation (Mississippian)

16-1

SOd

o o

Dg ~T Guilmette Formation (Devonian)

Dolomite (Silurian and Ordovician)

Eureka Quartzite (Ordovician)

Contact

Fault Bar and ball on downthrown side

Lineament interpreted from aerial photographs

Early to middle Eocene unconformity

Figure 3 (above and facing page). Geologic map of the Nanny 

Creek area, northern Pequop Mountains, Nevada.

FeO*

MgO

Figure 4. AFM ([Na2O+K2O]-total iron as FeO-MgO) diagrams 

using recalculated major oxide analyses for samples from the 

central part of the middle Eocene Northeast Nevada volcanic field. 

Recalculated using method of Sidder (1994); calc-alkaline trend 

from Irvine and Baragar (1971). A, All analyses from numbered 

localities shown in figure L4 within the central part of the Northeast Nevada volcanic field. B, Analyses from Nanny Creek type 

area.

12-

4H

Dacite n=92

54

\ ' I r I ^ I ' I 

58 62 66 70 74

Si02, IN WEIGHT PERCENT

78

A

12-

4-

Rhyolite

n=24

54 58

1 ' I ^ 1 ' I 

62 66 70 74 

Si02, IN WEIGHT PERCENT

78

B

Figure 5. Total-alkali (Na2O+K2O)-(SiO2) diagrams using recalculated major oxide analyses for samples from the central part of 

the middle Eocene Northeast Nevada volcanic field. Recalculated 

using method of Sidder (1994); rock classification grid from Le Bas 

and Streckeisen (1991). A, All analyses from numbered localities 

shown in figure LA within the central part of the Northeast Nevada 

volcanic field. B, Analyses from Nanny Creek type area.

Propylitic alteration has affected andesite and dacite in 

the northern East Humboldt Range (table 3, sample 90B31B) 

and elsewhere in the study area. These rocks are commonly 

green, typically yield more than 2.0 weight percent volatiles 

(loss on ignition or LOI), and have total alkali-silica compositions in or near the trachytic field. Silicified ash-flow tuffs 

may also be green; however, they have conchoidal fracture 

and porcellaneous matrix. They typically contain more than 

76 weight percent SiC>2 but still plot in the rhyolitic field of 

the total alkali-silica diagram.

Major oxide analyses presented in tables 2 and 3 are 

unconnected for loss of volatiles and were obtained by 

X-ray fluorescence techniques in analytical laboratories of 

the U.S. Geological Survey, Denver, Colorado; analytical 

methods, accuracy, and precision are as described by Taggait and others (1987). Trace element contents (tables 2, 3) 

were determined by energy-dispersive X-ray fluorescence
K8 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

16

12

36

Rhyolite

44 52 60 68 

Si02, IN WEIGHT PERCENT

76 84 36

Rhyolite

52 60 

Si02, IN WEIGHT PERCENT

16

B

44 52 60 68 

Si02, IN WEIGHT PERCENT

76 36

Rhyolite

44 52 60 68 

Si02, IN WEIGHT PERCENT

76 84

16

Q-12

O 4

CM H

v

JS 36

Rhyolite

44 52 60 68 

Si02, IN WEIGHT PERCENT

76

12

36 44 52 60 68 

Si02, IN WEIGHT PERCENT

76

g 16

o

cc.

LU 

D. 12

I

!°36

D

Rhyolite

44 52 60 68 

Si02, IN WEIGHT PERCENT

76

16

36

H

44 52 60 68 

Si02, IN WEIGHT PERCENT

76

Figure 6 (above and facing page). Total-alkali 

-(SiO2) diagrams using recalculated major oxide analyses for samples from the central part of the middle Eocene Northeast Nevada 

volcanic field. Recalculated using method of Sidder (1994); rock 

classification grid from Le Bas and Streckeisen (1991). Localities 

are shown in figure L4. A, Southern Snake Mountains. B, Northern

East Humboldt Range. C, Southern East Humboldt Range. D, 

Deadman Creek. E, Deadman Creek (samples received from K. 

Mueller, University of Wyoming). F, Wood Hills. G, Ferguson 

Mountain and Dolly Varden Mountains. //, Silver Island Mountains, Utah. /, Sanford Springs. J, Gold Hills area. K, Coal Mine 

Canyon, northern Adobe Range.
NORTHEAST NEVADA VOLCANIC FIELD K9

Table 1. Regional summary of localities at which Eocene volcanic rocks have been dated, northeast Nevada and adjacent Utah. 

[Leaders ( ) indicate not described]

Date (Ma)

37.3

37.5

38.4

38.8

38^3

39.6

39.9

41.8

42.5

Method

K-Ar, biotite

K-Ar, -

K-Ar, biotite

K-Ar, biotite

K-Ar, -

K-Ar, biotite

K-Ar, biotite

Fission track, zircon

K-Ar, biotite

Rock type

Tuff

Dacite

Andesite

-

Rhyolite

Tuff

Rhyodacite

-

Locality

Cottonwood area, Wasatch Range, Utah (Crittenden and others, 1973).

Roberts Mountains, Nevada (Maher and others, 1990).

Snowstorm Mountains, Nevada (Wallace, 1993).

Bingham, Utah (James and others, 1961).

Tuscarora area-Bull Run Mountains, Nevada (McKee and others, 1976).

Owyhee, Nevada (Coats, 1971).

Jarbridge, Nevada (Coats, 1964).

Drum Mountains, Utah (Lindsey, 1982).

Bull Run Mountains, Nevada (Axelrod, 1966).

16

9,0

36

CM 0

36

Rhyolite

44 52 60 68 

Si02, IN WEIGHT PERCENT

76

Rhyolite

44 52 60 68 

Si02, IN WEIGHT PERCENT

76

spectroscopy (Elsass and duBray, 1982) using 109Cd and 

241 Am sources; accuracy and precision of these analyses 

are as described by Sawyer and Sargent (1989). Chemical 

data are for crushed bulk-rock samples from which 

xenocrystic fragments were hand picked from the ash-flow 

tuff samples.

Major oxide analyses shown in tables 2 and 3 were corrected for volatiles and plotted on AFM ([Na2O+K2O]-total 

iron as FeO-MgO] and total alkali (Na2O+K2O)-silica 

(SiO2) diagrams using a petrologic recalculation program 

(Sidder, 1994). The AFM plots show the regional, 

calc-alkalic, subduction-related character of the central part 

of the Northeast Nevada volcanic field (fig. 4A). Analyses 

from the Nanny Creek type area show a similar trend (fig. 

4B). The andesitic-dacitic-rhyolitic composition of the volcanic rocks from the central part of the Northeast Nevada 

volcanic field and the Nanny Creek type area is shown in the 

total alkali-silica diagrams (figs. 5A, B). Classification of the 

volcanic rocks at each numbered locality is shown in a series 

of total alkali-silica diagrams (fig. 6). The analysis of the 

Eocene pyroxene diorite from the southern East Humboldt 

locality (loc. 4, fig. 1A) was not plotted.

Z 16

Rhyolite

36

K

44 52 60 68 

Si02, IN WEIGHT PERCENT

76
Table 2. Chemical analyses of Eocene volcanic rocks from the Nanny Creek type area, Northeast Nevada volcanic field.

[Location of areas shown in figure IA. Major oxides (weight percent, uncorrected) determined by X-ray spectroscopy; analysts D.F. Siems and J.E. Taggart; FeTOs 

error is 10 percent of value listed or ±6 (Rb), ±5 (Sr), ±4 (Y), ±3 (Zr), ±3 (Nb), and ±10 (Ba), whichever is greater. Asterisk (*) indicates dated sample (table 4). M

figure 3]

Map unit 

Lab No.

Field No. ------

Latitude -

Longitude 

Tl

D-323634

QQT <A* ool jo*

41°01'30"N.

114°32'47"W.

Tl

D-365204

90B6

41°01'38"N.

114°32'54"W.

Tl

D-365205

90B11

41°00'34"N.

114°32'05"W.

T2

D-323633

COT CC=|c

oo 1 OJ

41°01'29"N.

114°32'41"W.

T2

D-365206

90B3

41°00'42"N.

114°32'27"W.

T2

D-365207

Qnr>7 A y\)D / /\

41°01'38"N.

114°32'45"W.

T

D-36

Qrv

y\JD 

41°01

114°32

Major-oxide composition

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K20

TiO2

P205

MnO

LOI

Total

71.4

14.2

1.78

0.53

2.29

3.18

4.14

0.37

0.11

0.02

0.96

99.98

67.6

16.6

1.80

0.66

2.75

3.81

4.13

0.45

0.14

0.02

1.48

99.44

67.3

15.6

2.57

0.60

2.54

3.46

4.09

0.39

0.14

0.02

2.41

99.12

78.0

11.6

0.45

0.12

0.76

2.46

5.36

0.1

0.05

0.02

0.67

99.59

75.0

12.8

0.93

0.29

0.88

3.08

5.12

0.10

0.05

0.04

1.25

99.54

76.5

11.6

0.74

0.24

0.87

2.52

5.29

0.09

0.07

0.02

1.01

98.95

75

11

0

0

2

5

0

0

0

98

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

114

408

21

212

8

1,974

144

598

20

276

15

2,110

157

573

24

252

12

2,550

152

109

18

99

12

605

201

163

22

141

15

1,043

203

154

25

120

14

915

251

130

23

114

11

711
Table 2. Chemical analyses of Eocene volcanic rocks from the Nanny Creek type area, Northeast Nevada volcanic field Continued

Map Unit 

T ah Nr> \-id\) 1NU. 

Field No. 

Latitude - 

Longitude 

T2

D-365210

90B13

41°01'55"N.

114°32'39"W.

T3x

D-365219

90B5

41°01'07"N.

114°32'25"W.

T3x

D-365220

QOR1QA :7\JLJ 1 7 r\

41°01'23"N.

114°31'40"W.

T3x

T~\ O /CC-">^ 1 D-365221

41°01'23"N.

114°31'40"W.

T3x

D 357055

QOR'MA y\JLj £.^r\

41°01'28"N.

114°32'30"W.

T3x

D-357056

90B24B

41°01'28"N.

114°32'30"W.

T

D 50

91T

41°03

114°30

Major-oxide composition

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P2O5

MnO

LOI

Total

75.2

12.4

1.15

0.19

0.89

3.04

4.85

0.10

0.05

0.02

1.55

99.44

61.3

16.3

4.89

2.54

5.59

3.52

2.09

0.59

0.19

0.07

2.66

99.74

60.3

16.0

5.51

3.14

6.08

2.91

1.71

0.64

0.17

0.08

3.69

100.23

64.6

16.5

3.68

1.45

5.80

3.50

2.09

0.64

0.18

0.04

1.10

99.58

60.3

16.8

5.37

2.86

5.70

3.20

2.13

0.66

0.21

0.10

2.71

100.04

60.8

16.4

5.45

2.93

5.73

3.20

2.42

0.66

0.23

0.09

2.27

100.18

61

16

4

2

4

3

2

0

0

2

98

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

208

157

20

126

14

952

62

525

18

168

7

1,348

54

544

22

154

12

1,136

65

509

24

147

8

1,462

81

574

21

181

9

1,240

95

552

18

171

7

1,243

73

526

20

124

10

2,910
Table 2. Chemical analyses of Eocene volcanic rocks from the Nanny Creek type area, Northeast Nevada volcanic field Continued

Map Unit -

Lab No.

Field No. 

Latitude - 

Longitude -----

T3a

D-357054

90B9B*

41°01'34"N.

114°32'36"W.

T3a

T~\ O/^CO 1 O U 365212

90B10

41°01'36"N.

114°32'08"W.

T3a

D-365213

nr\r> 1 1 yum /

41°01'56"N.

114°32'25"W.

T3a

D-365214

90B20

41°01'33"N.

H4°31'44"W.

T3a

D-365215

90B25

41°03'03"N.

114°31'43"W.

T3a

D O/^CT 1 O 

 3652 IS

90B27

41°02'10"N.

T

D-36

90B2

41°02'

114°30

Major-oxide composition

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

LOI

Total

74.8

12.5

1.35

0.23

0.89

2.86

5.16

0.10

0.05

0.02

1.65

99.61

73.8

11.3

1.16

0.51

1.38

1.44

4.93

0.15

0.06

0.02

4.69

99.44

76.0

11.8

0.67

0.17

0.96

2.62

5.02

0.11

0.05

0.02

1.69

99.11

79.0

10.2

0.34

0.10

0.12

1.21

7.12

0.08

0.05

0.02

1.27

99.51

75.7

11.1

1.12

0.22

0.74

1.64

6.55

0.13

0.14

0.02

1.74

99.10

68.4

13.3

2.07

0.79

1.80

2.26

4.05

0.10

0.08

0.04

6.90

99.79

70.

14

2

0

3

3

2

0

0.

0

1

99.

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

205

143

22

128

12

773

115

480

18

149

14

1,941

177

176

18

143

17

1,146

183

79

14

121

11

895

200

153

21

146

11

1,499

146

246

16

110

13

1,658

110

450

17

133

9

1,468
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field.

[Location of areas shown in figure IA. Major oxides (weight percent, uncorrected) determined by X-ray spectroscopy; analysts D.F. Siems, J.S. Mee, and I.E. Tagg

reported as Fe2C>3. LOI (weight percent), loss on ignition at 925°C. Rb, Sr, Y, Zr, and Nb (parts per million) determined by energy-dispersive analysis, 109Cd and 24

LaRock and K. Woodburne; error is 10 percent of value listed or ±6 (Rb), ±5 (Sr), ±4 (Y), ±3 (Zr), and ±3 (Nb), whichever is greater. Asterisk (*) indicates dated s

pyroxene diorite (table 7); t indicates sample received from K. Mueller, University of Wyoming; tt indicates sample received from P. Camilleri, Univiversity of W

Locality -

Field No. 

Lab No.

Latitude- - -

Longitude -

Southern Snake Mountains

QQT 1 1 OO 111

D-323620

41°07'35"N.

114°59'08"W.

OQT 'J /£* oo 1 36*

r\ ^ "> 'j /£ "> 1 L) j 23621

41°09'57"N.

114°57'06"W.

QQT ~11

001 J 1

V\ OT5/CT"> D 323622

41°10'02"N.

114°57'02"W.

QQT 10* OO 1 JO

D 323623

41° 1 OWN.

114°56'59"W.

OQT 39

D-323624

41°12'03"N.

H4°54'04"W.

QQT /in 001 ft\}

D 'J T2/^T C 323625 

41°12'04"N.

114°54'21"W.

88T

r\ m

u 32

41°12

114°54

Major-oxide composition

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

LOI

Total

68.0

11.6

3.01

0.76

1.59

1.09

4.65

0.41

<0.05

<0.02

8.45

100.43

81.7

8.63

0.66

0.11

0.30

0.83

6.25

0.08

0.06

<0.02

0.69

99.33

61.9

16.4

5.67

1.57

3.66

3.89

3.91

0.55

0.16

<0.02

2.24

99.97

77.1

11.2

1.39

0.11

0.23

0.53

6.77

0.11

0.13

0.04

1.72

99.33

75.6

12.1

1.61

<0.10

1.07

2.81

5.03

0.34

0.07

<0.02

0.48

99.23

62.1

17.6

5.06

0.67

4.19

3.93

3.41

0.77

0.31

0.03

1.57

99.64

79

9

0

0

0

0

6

0

0

<0

1

99

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

221

170

52

464

*37

1,288

131

54

8

82

9

836

89

303

11

121

6

860

117

40

13

114

13

837

134

139

34

408

20

1,975

94

450

19

157

9

1,216

168

60

23

91

6

876
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field Continued.

Locality

Field No. 

I nK V[n \-ia\j rNu. 

Latitude -

Longitude ~

Northern East Huraboldt Range

QOFH1 A 7\JLjJ 1/A

D-357057

41°02'50" N.

115°04'10"W.

90B31B*

D 357058

41°02'50"N.

115°04'10"W.

91T11

D-503360

40°42'09" N.

115°04'20"W.

91T12*

D-503361

40°42'11"N.

115°04'22"W.

Southern East Huraboldt Range

91T13

D-503362

40°41'10"N.

115°03'47"W.

91T14

D 503363

40°40'10"N.

115°02'40"W.

91T

D-50

40°39'

115°06

Major-oxide composition

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K2O

TiO,

P205

MnO

LOI

Total

62.0

16.5

5.52

1.80

4.48

4.45

1.64

0.69

0.19

0.08

2.62

99.97

65.4

14.2

3.85

1.37

3.49

1.53

2.32

0.39

0.15

0.02

6.67

99.39

61.7

16.0

4.92

1.77

3.74

3.46

2.94

0.61

0.17

0.06

3.45

98.82

61.1

16.3

5.12

2.77

5.19

3.90

1.26

0.62

0.17

0.10

2.77

99.3

60.6

16.4

5.59

3.11

5.66

3.58

1.84

0.70

0.19

0.12

1.59

99.38

59.0

16.7

5.68

3.53

6.06

3.50

2.10

0.83

0.24

0.11

1.45

99.2

66

15

2

0

2

3

3

0

0

0

3

99

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

43

481

16

158

5

1,083

114

2,965

12

194

10

2,239

77

341

18

140

12

1,286

70

404

11

139

11

1,235

80

402

17

122

15

1,168

84

653

18

133

8

1,544

95

320

12

160

12

1,527
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field Continued.

Locality

Field No. 

Lab No. -

Latitude 

Longitude ~

Southern East Humboldt Ranee

91T19*

D-503366

40°41'48" N.

H5°04'44" W.

91T20

D-503367

40°41'22" N

115°05'22" W.

91T22§

D-503368

40°38'33" N.

115°05'28" W.

91T23

D 503369

40°38'29" N.

115°05'25" W.

92B42

D-522594

40°41'33" N.

115°04'33" W.

92B45

D-522595

40°41'39" N.

115°03'50" W.

92

D-52

40°41

115°05

Major-oxide composition

SiO2

A1203

FcTO3

MgO

CaO

Na2O

K26

TiO2

P2O5

MnO

LOI

Total

71.4

12.4

2.00

0.88

2.85

2.25

4.10

0.39

0.14

0.05

2.25

98.71

67.5

13.8

1.44

0.72

3.06

2.20

3.00

0.13

0.08

0.02

6.81

98.76

53.2

17.0

5.32

3.34

13.3

3.73

1.38

0.45

0.27

0.08

0.76

98.83

58.4

17.0

5.91

2.48

5.30

3.56

2.32

0.81

0.24

0.07

3.18

99.27

67.3

12.6

1.55

1.05

2.66

0.67

4.09

0.19

0.11

0.02

8.80

99.04

62.8

15.7

4.29

2.20

2.88

2.54

5.07

0.68

0.19

0.04

3.09

99.48

72

11

0

0

0

7

0

0

0

4

99

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

89

509

13

160

11

1,941

57

1,101

10

74

10

1,474

35

1,948

11

84

4

696

50

554

19

120

10

1,505

126

763

18

129

9

1,261

106

277

12

94

6

1,112

138

137

18

63

12

1,175
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field Continued.

Locality

Field No. 

I ih Nn L-«aU 1NO. - 

Latitude - 

Longitude -- 

Southern East 

Humboldt Range

92B57 

D 522599

40°38'27"N.

115°10'00"W.

Deadman Creek area

HI 

D-365192

41°15'N.

114°37'30"W.

H2 

D-365193

41°15'N.

114°37'30"W.

H3 

D-365194

41°15'N.

114°37'30"W.

H4 

D-365195

41°15'N.

114°37'30"W.

H6 

D-365196

41°15'N.

114°37'30"W.

we 

D-36

41°18

114°38

Major-oxide composition

SiO2

A12 03

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P2O5

MnO

LOI

Total

65.2

15.7

3.76

1.58

3.79

3.22

3.61

0.54

0.16

0.06

1.97

99.59

62.4

16.8

5.67

1.29

2.11

5.07

2.51

0.65

0.21

0.05

2.50

99.26

74.9

12.4

1.11

0.43

0.71

2.32

5.00

0.11

0.06

<0.02

2.22

99.28

63.9

14.6

4.15

0.78

3.59

3.27

4.47

0.60

0.21

0.10

3.70

99.37

78.1

11.1

0.84

0.24

0.55

2.96

3.77

0.09

<0.05

<0.02

1.61

99.33

62.5

17.9

4.46

1.62

1.39

8.17

0.49

0.59

0.19

0.18

1.85

99.34

71

13

0

2

3

3

0

0

0

0

98

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

106

298

22

139

15

988

75

494

21

190

11

1,754

167

266

23

141

15

1,611

137

343

21

197

12

1,721

118

226

27

118

16

1,115

17

296

14

105

15

650

138

482

23

253

9

1,873
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field Continued.

Locality 

Field No. 

Lab No.

Latitude -

Longitude 

HOL-51

D-365199

41°14'48"N.

114°37'27"W.

90-141

D-365200

41°16'28"N.

1 14°4Q' W.

Deadman Creek area

90-22f

D-365201

41°17'18"N.

114°39'59"W.

Wood Hills

90-67|

D 365202

41°18'58"N.

114°39'55"W.

on TQ+ y\} /By

D O/^CO AT 3o5ZUj

41°18'44"N.

114°38'32"W.

92BWHl*tt

D-522590

41°04'53"N.

114°52'55"W.

nTD\\

yzrJW

D-5

41°04

114°5

Major-oxide composition

Si02

A12O3

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

LOI

Total

74.8

12.7

1.13

0.38

0.57

2.26

5.78

0.10

0.05

0.02

1.86

99.65

70.7

12.1

1.16

0.58

1.40

0.85

6.53

0.12

0.05

0.02

5.71

99.22

67.5

13.7

4.10

1.33

3.95

2.80

3.43

0.58

0.22

0.02

1.58

99.21

72.7

11.8

2.97

1.04

2.95

2.27

3.81

0.51

0.19

0.02

1.14

99.4

67.6

15.7

2.74

0.60

2.32

3.65

4.92

0.40

0.18

0.05

1.04

99.2

75.2

12.6

1.44

0.19

0.91

3.15

4.86

0.15

0.05

0.04

0.93

99.52

6

1

9

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

176

217

21

139

18

1,596

191

809

17

146

12

1,195

133

634

23

157

13

1,810

143

490

21

162

10

1,394

165

519

28

278

15

2,096

140

125

14

113

13

1,274

7

38

1

13

1,04
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field Continued.

Locality 

Field No. 

T ah Nn

Dolly Varden 

Mountains

92BDV*

40°19'20"N.

114°31'09"W.

Silver Island Mountains

91T3*

D 503357

40°49'59" N.

113°56'49"W.

91T4*

D 503358

40°49'56" N.

113°57'24"W.

91T30

D 503370

39°48'26" N.

114°08'15"W.

Sanford Springs area, southern Deeo Creek Moun

91T32

D 503371

39°48'23" N

114°08'15"W.

91T33

D-5Q3372

39°48'35" N.

114°08'25"W.

92B

D-51

114°10

Major-oxide composition

SiO2

A1203

FeTO3

MgO

CaO

Na2O

K2O

TiO2

P2O5

MnO

LOI

Total

64.1

15.2

4.46

2.04

3.74

2.84

3.03

0.55

0.15

0.06

3.16

99.33

59.2

17.6

6.06

2.79

6.04

3.14

2.09

0.62

0.19

0.11

1.30

99.14

68.0

14.9

2.31

0.88

2.99

3.15

2.84

0.21

0.11

0.07

3.53

98.99

60.8

15.9

5.56

3.71

5.73

3.38

2.55

0.78

0.20

0.08

0.81

99.5

59.8

16.0

5.31

3.80

5.76

3.03

2.75

0.76

0.21

0.08

1.41

98.91

60.0

16.0

5.44

3.61

5.84

2.76

2.47

0.75

0.19

0.09

2.22

99.37

66

15

4

1

3

3

4

0

0

0

<0

99

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

109

230

24

182

19

977

67

368

19

132

10

1,047

84

275

9

122

15

1,045

83

490

30

194

15

1,143

94

513

21

190

13

1,195

75

463

24

174

5

979

189

331

32

234

18

1,163
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field Continued.

Locality 

Field No. -

Lab No.

Latitude - 

Longitude 

Sanford Sorinas area, southern Deeo Creek Mountains

92B15

D-5 16490

39°54'16"N.

OO13 1 £. 92B1O

D 516484

39°57'13"N.

114°07'07"W.

92B19

D-5 16485

39°57'43"N.

114°06'42"W.

92B21

D-5 16491

39°58'13"N.

114°07'56"W.

92B24

D-5 16486

39°59'59" N.

114°07'53"W.

92B26

D-5 16487

39°59'23" N.

114°04'50"W.

92B

D-5 

39°48

114°07

Major-oxide composition

SiO2

A1203

FeT03

MgO

CaO

Na2O

K2O

TiO2

P205

MnO

LOI

Total

66.4

14.8

4.28

0.80

2.95

2.93

4.82

0.52

0.19

0.08

1.26

99.03

67.0

14.8

3.53

0.94

2.63

3.05

4.91

0.45

0.18

0.06

1.51

99.06

64.0

15.1

4.43

2.03

3.64

2.77

3.03

0.55

0.15

0.06

3.55

99.31

61.3

14.6

5.33

2.13

5.59

2.85

4.11

0.64

0.29

0.1

1.81

98.75

65.4

14.8

3.63

1.26

2.94

2.99

4.73

0.45

0.18

0.07

2.56

99.01

69.0

13.8

2.55

0.11

3.07

3.28

5.22

0.20

0.10

0.08

1.48

98.89

69

13

1

1

2

2

2

0

0

0

4

99

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

198

269

27

205

21

1,245

206

281

23

210

21

1,239

194

255

26

197

18

1,208

167

350

21

201

16

1,576

206

276

25

218

20

1,141

241

157

22

192

22

981

78

373

14

114

8

1,343
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada volcanic field Continued.

Locality -

Field No. 

Lab No.

Sanford Sorines area, southern Deeo Creek Mountains

92B33 

D-5 16497 

39°48'09" N. 

114°07'50"W.

92B34 

D-5 16496 

39°48'16"N. 

H4°07'44"W.

92B38 

D-5 16499 

39°49'29" N. 

114°07'31"W.

92B60 

D 516492 

39°59'20" N. 

114°08'04"W.

92B62 

D-5 16493 

39°52'30" N. 

114°10'37"W.

92B69 

D-5 16494 

39°51'39"N. 

114°09'49"W.

92B

D-5 1

39°51'4

114°09'

Major-oxide composition

SiO2 

A1 203 

FeTO3 

MgO 

CaO

Na2O 

K^O

Ti02 

P205 

MnO

LOI

Total

62.8 

15.9 

4.11 

2.66 

4.63

3.16 

2.86

0.61 

0.19 

0.07

2.38

99.37

60.7 

16.1 

4.86 

3.01 

5.37

2.81 

2.83

0.72 

0.20 

0.08

2.96

99.64

67.4 

11.1 

1.42 

1.12 

5.00

1.35 

3.06

0.20 

0.11 

0.02

8.48

99.26

64.5 

14.3 

5.05 

1.93 

3.88

2.80 

4.46

0.55 

0.23 

0.09

1.36

99.15

65.0 

14.6

4.45 

1.06 

3.72

2.93 

4.82

0.51 

0.18 

0.09

1.49

98.85

65.0 

14.9 

4.51 

2.65 

4.14

3.02 

3.43

0.73 

0.19 

0.07

0.55

99.19

70.

13.

2.

0.

2.

3.

4.

0.

0.

0.

0.

99.

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

91

513

15

182

16

1,288

76

475

24

165

10

827

60

637

13

93

12

1,761

195

226

26

198

24

1,138

191

284

31

210

16

1,277

136

383

23

225

15

1,162

194

224

24

213

21

423
Table 3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevada 

volcanic field Continued.

Locality 

Field No. 

Lab No. -

Sanford Springs 

area

92B67 

D-5 16500 

39°48'15"N.

Gold Hill area

91CP30* 

D-522592 

40°11'23"N. 

114°58'15"W.

91CP33* 

D-522593 

40°12'18"N. 

114°58'15"W.

Coal Mine Canyon

12247 

D-559062 

41°07'N. 

115°37'57"W.

12624* 

D 559063 

41°06'52"N. 

115°37'46"W.

Major-oxide composition

SiO^

A1203 

FeTO3 

MgO 

CaO

Na20 

K2O

P2O5

MnO

LOI

Total

65.6

12.6 

1.62 

1.81 

5.88

2.58 

2.44 

0.22

0.12

0.03

6.23

99.13

62.2

15.8 

5.16 

2.68 

5.19

2.82 

2.73 

0.63

0.15

0.1

2.06

99.52

68.5

15.0 

1.68 

0.72 

2.47

2.87 

3.95 

0.33

0.12

0.05

2.93

98.62

65.7

15.4 

3.46 

1.04 

2.92

2.61 

5.16 

0.67

0.23

0.04

1.79

99.02

65.6

15.2 

3.54 

1.17 

3.11

2.58 

4.85 

0.65

0.23

0.08

2.39

99.4

Trace element composition

Rb

Sr

Y

Zr

Nb

Ba

85

412

17

111

9

1,373

115

279

29

191

15

931

115

206

36

209

16

980

130

366

16

157

16

2,252

138

372

20

164

15

1,527
K22 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

Table 4. Summary of 4(1Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada

volcanic field.

[Location of areas shown in figure \A. Ferguson Mountain sampled by J. Welsh for 40Ar/39Ar date, (12659), resampled by C. Thorman for rock

chemistry (92T21). Dolly Varden Mountains sampled by J. Zamudio for' 

analyses performed by the U.S. Geological Survey, Denver]

'Ar/3 Ar date (3233), resampled by Brooks for rock chemistry (92BDV). All

Area

Nanny Creek

Nanny Creek

Nanny Creek

Nanny Creek

Southern Snake Mountains

Southern Snake Mountains

Southern Snake Mountains

Southern Snake Mountains

Northern East Humboldt Range

Southern East Humboldt Range

Southern East Humboldt Range

Southern East Humboldt Range

Deadman Creek Area,

Windermere Hills2

Deadman Creek Area,

Windermere Hills2

Wood Hills

Ferguson Mountain

Dolly Varden Mountains

Silver Island Mountains

Silver Island Mountains

Sanford Springs

Gold Hill

Gold Hill

Coal Mine Canyon

Sample no.

91T10

90B9B

88T55

88T56

88T36

88T42

88T41

88T38

90B31B

91T12

91T17

91T19

WC-6

WC-1

92BWH1

12659-92T21

3233-92BDV

91T3

91T4

92B27

91CP33

93CP30

12624

Rock type

Dacite

Ash-flow tuff

Ash-flow tuff

Ash-flow tuff

Ash-flow tuff

Dacite

Ash-flow tuff

Ash-flow tuff

Ash-flow tuff

Dacite

Dacite

Dacite 1

Dacite

Ash-flow tuff

Ash-flow tuff

Dacite

Dacite

Andesite

Rhyolite

Ash-flow tuff

Rhyolite

Dacite

Ash-flow tuff

Apparent age (Ma) 

Mineral and error (la) Character of spectrum

Hornblende

Biotite

Biotite

Biotite

Biotite

Biotite

Biotite

Biotite

Biotite

Hornblende

Hornblende

Biotite

Hornblende

Biotite

Biotite

Hornblende

Biotite

Hornblende

Biotite

Biotite

Biotite

Hornblende

Hornblende

39.23±0.5

39.61±0.13

39.89+0.12

41.08+0.11

39.5±0.2

39.7±0.1

39.76±0.13

39.85±0.15

38.0±0.5

38.8+0.4

39.5+0.3

40.98±0.1

39.87±0.1

40.38±0.1

39.7±0.1

39.80±0.1

39.08±0.11

42.6±0.3

42.61±0.8

40.64+0.07

39.58±0.10

39.6±0.2

40.4±0.2

Plateau date; 87 percent of total 39ArK

Plateau date; 60 percent of total 39ArK

Plateau date; 94 percent of total 39ArK

Plateau date; 86 percent of total 39ArK

Plateau date; 95 percent of total 39ArK

Preferred date for disturbed spectrum;

60 percent of total 39ArK

Plateau date; 63 percent of total 39ArK

Preferred date for disturbed spectrum;

80 percent of total 39ArK

Preferred date for disturbed spectrum;

54 percent of total 39ArK; probably a

minimum

Plateau date; 71 percent of total 39ArK

Plateau date; 92 percent of total 39ArK

Plateau date; 52 percent of total 39ArK

Plateau date; 77 percent of total 39ArK

Plateau date; 64 percent of total 39ArK

Preferred date for disturbed spectrum;

excess argon, maximum estimate

Plateau date; 62 percent of total 39ArK

Plateau date; 94 percent of total 39ArK

Plateau date; 81 percent of total 39ArK

Preferred date for disturbed spectrum

Plateau date; 92 percent of total 39ArK

Plateau date; 74 percent of total 39ArK

Plateau date; 63 percent of total 39ArK

(recalculated)

Plateau date; 93 percent of total 39ArK

'Dacite clast in basal conglomerate. 

2Mueller, (1992).
NORTHEAST NEVADA VOLCANIC FIELD K23

Table 5. Abbreviated 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada 

volcanic field.

[Location of areas shown in figure I A; reactor package (table 6) is given following sample number. Age-spectrum data for Deadman Creek are given in 

Mueller (1992). 40ArR, radiogenic 4()Ar; 39ArK, potassium-derived 39Ar; F, 40ArR divided by 39ArK; Ma error to Id. Leaders (-) indicate unmeasurable; 

asterisk (*) indicates step used in plateau-date or preferred-date calculation]

Temperature

4°ArR 39ArK F 39Ar/37Ar 40ArR (percent) 39Aric (percent)

Apparent age 

and error (Ma)

NANNY CREEK

Sample 91T10/66/DD37; dacite; 289.2 mg hornblende; measured 4()Ar/36Ar=296;

J-value=0.007781±0.1 percent (la);

800

900

1,000

1,050

*1,100

*1,150

*1,175

* 1,200

* 1,250

1,350

0.12980

0.02139

0.01992

0.03779

0.11208

1.2323

1.7275

0.59157

0.97129

0.54260

plateau date=39.23±0.5 Ma;

lat 41°1'28" N., long 1 14°30'10" W.

0.04291

0.00710

0.00949

0.00977

0.03966

0.43526

0.61377

0.20750

0.34404

0.18741

Total gas

Sample 90B9B/32/DD28; ash-flow tuff; 58 mg biotite

J-value=0.007317±0.1 percent (la);

650

750

850

900

950

1,000

1,050

*1,100

*1,150

* 1,300

0.01982

0.06042

0.37870

0.85369

0.63085

1.4416

1.3049

1.6431

3.3623

2.1992

3.025 2.5

3.01 1.10

2.10 0.41

3.87 0.34

2.82 0.20

2.831 0.15

2.815 0.15

2.851 0.15

2.823 0.15

2.895 0.15

2.839

; measured 40Ar/36Ar=296.6

23.2

20.9

27.4

61.8

65.2

85.8

93.2

88.2

92.8

93.6

2.3

0.4

0.5

0.5

2.1

22.9

32.4

10.9

18.1

9.9

42±1

42±8

29±7

54±5

39±2

39.3±0.2

39.08±0.11

39.6±0.4

39.2±0.2

40.2±0.5

39.4±0.3

; plateau date=39.61±0.13 Ma;

lat 41°1'23"N., long 114°31'40"W.

0.02023

0.03948

0.12920

0.27621

0.20521

0.47145

0.42834

0.54138

1.1085

0.72483

Total gas

Sample 88T55/21/DD9; ash-flow tuff; 89.8 mg biotite

J-value=0.007447±0.25 percent (la)

500

600

700

*750

*800

*850

*900

*950

* 1,000

* 1,050

*1,150

1,300

0.15838

0.23313

1.6435

3.6428

3.7730

3.0798

3.5829

5.7707

9.8746

5.8823

1.9717

0.04820

;lat41°l'29"N.,

0.10844

0.10217

0.55134

1.2111

1.2561

1.0239

1.1930

1.9131

3.2973

1.9644

0.65648

0.01555

Total gas

0.98

1.530

2.931

3.091

3.074

3.058

3.046

3.035

3.033

3.034

3.015

; measured 4()Ar/36Ar=298.9

long 114°32'41"W.

1.470 26

2.282 64

2.981 201

3.008 417

3.004 483

3.008 542

3.003 433

3'.016 253

2.995 176

2.994 101

3.003 27

3.10 8.1

2.984

9.0

27.6

47.6

76.6

86.7

94.2

92.2

90.8

90.9

92.2

0.5

1.0

3.3

7.0

5.2

12.0

10.9

13.7

28.1

18.4

13±2

20±2

38.28±0.15

40.34±0.08

40.1 ±0.3

39.92+0.09

39.77+0.06

39.62+0.13

39.60±0.07

39.6±0.2

39.4±0.2

; plateau date=39.89±0.12 Ma;

5.0

8.6

32.1

58.0

61.7

58.0

61.3

67.5

73.1

76.3

78.6

10.9

0.8

0.8

4.1

9.1

9.4

7.7

9.0

14.4

24.8

14.8

4.9

0.1

19.6±0.3

30.4±0.8

39.61+0.12

'39.96±0.11

39.91±0.15

39.96±0.11

39.90±0.11

40.08±0.13

39.79+0.11

39.79±0.11

39.90+0.13

41±6

39.65+0.13
K24 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

Table 5. Abbreviated 4(>Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada 

volcanic field Continued.

Temperature

"ArR yArK 39Ar/37Ar ATR (percent) AFR (percent)

Apparent age 

and error (Ma)

NANNY CREEK Continued

Sample 88T56/16/DD12; ash-flow tuff; 79.3 mg biotite; measured 4llAr/j6Ar=298.9; plateau date=41.08±0.11 Ma 

J-value=0.007342±0.25 percent (la); lat 41°1'30" N., long 114°3247" W.

500

600

700

750

800

850

*900

*950

* 1,000

* 1,050

*1,150

1,300

0.05826

0.07291

0.38815

0.64068

1.2601

2.4142

3.6391

4.6752

6.0889

7.3773

9.7167

0.50310

Total gas

0.03447

0.02416

0.12254

0.20074

0.39691

0.76145

1.1572

1.4903

1 .9407

2.3564

3.0952

0.15804

1.69

3.02

3.168

3.192

3.175

3.169

3.145

3.137

3.138

3.131

3.139

3.183

3.138

20

40

66

118

162

227

277

272

163

88

50

28

12.9

36.6

40.6

79.0

84.6

91.0

93.0

92.9

89.9

85.3

87.7

54.4

0.3

0.2

1.0

1.7

3.4

6.5

9.9

12.7

16.5

20.1

26.4

1.3

22±2

40±2

41.5±0.6

41.8±0.3

41.57±0.15

41.50±0.13

41.18±0.12

41.08±0.11

41.09±0.11

41.00±0.11

41.11±0.11

41.7±0.4

41.09±0.13

SOUTHERN SNAKE MOUNTAINS

Sample 88T36/18/DD12; ash-flow tuff; 87 mg biotite; measured 4()Ar/36Ar=298.9; no plateau; preferred date=39.5±0.2 Ma; 

J-value=0.007163±0.25 percent (la); lat 41°9'57" N., long 114°57'6" W.

500

600

700

750

800

850

900

950

* 1,000

* 1,050

*1,150

* 1,300

0.30420 

0.77060 

6.6119 

5.7352 

4.1256 

2.6844 

1.8721 

0.79985 

4.5589 

5.6361 

4.3953 

0.33488 

Total gas

0.17163

0.29229

2.1322

1.8427

1.3290

0.86756

0.61022

0.26451

1.4774

1.8242

1.4164

0.10708

1.772

2.667

3.101

3.112

3.104

3.094

3.068

3.024

3.086

3.090

3.103

3.127

3.067

30

13

72

230

210

161

98

85

65

25

9.9

9.2

27.8

63.5

85.9

94.0

94.1

91.9

87.0

83.5

85.4

90.7

93.2

76.6

1.4

2.4

17.3

14.9

10.8

7.0

4.9

2.1

12.0

14.8

11.5

0.9

22.76±0.07

34.1 ±0.2

39.63±0.11

39.78±0.11

39.68±0.11

39.55±0.15

39.21±0.15

38.7±0.3

39.44±0.14

39.49±0.11

39.66±0.11

40.0±0.7

39.21±0.12

Sample 88T42/20/DD12; dacite; 102.3 mg biotite; measured 40Ar/36Ar=298.9; minor excess 40Ar; preferred date=39.7±0.1 Ma; 

J-value=0.007268±0.25 percent (la); lat 41°12'2" N., long 114°5443" W.

500

600

700

750

800

850

900

950

1,000

1,050

1,150

1,300

0.37846 

0.61035 

1.5013 

1.6668 

2.0437 

2.2285 

2.6020 

3.7744 

6.8916 

5.9272 

13.640 

1.5217 

Total gas

0.23817

0.31737

0.57354

0.55909

0.65713

0.71080

0.83967

1.2271

2.2531

1.9190

4.3898

0.48327

1.589

1.923

2.618

2.981

3.110

3.135

3.099

3.076

3.059

3.089

3.107

3.149

3.020

21

16

27

48

72

91

106

111

114

116

78

47

17.8

38.3

52.0

72.6

83.7

88.3

88.5

87.3

83.8

88.7

92.3

86.4

1.7

2.2

4.0

3.9

4.6

5.0

5.9

8.7

15.9

13.5

31.0

3.4

20.7±0.2

25.0±0.3

34.00±0.13

38.67±0.14

40.32±0.13

40.65±0.12

40.18±0.12

39.89±0.11

39.66±0.11

40.05±0.11

40.29±0.11

40.8±0.2

39.17±0.12
NORTHEAST NEVADA VOLCANIC FIELD K25

Table 5. Abbreviated 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada 

volcanic field Continued.

Temperature Apparent age 

(°C)______4"ArR_________39ArK_________F______39Ar/37Ar 40ArR (percent) 39ArK (percent) and error (Ma)

___________________________SOUTHERN SNAKE MOUNTAINS Continued___________________________

Sample 88T41/14/DD12; ash-flow tuff; 101.6 mg biotite; measured 40Ar/36Ar=298.9; plateau date=39.76±0.13 Ma;

J-value=0.007208±0.25 percent (la); lat 41°12'4" N., long 114°54'36" W.

500 0.17167 0.11099 1.547 58 22.1 0.7 20.0±0.6 

600 0.39633 0.17888 2.216 66 42.2 1.2 28.6±0.2 

650 0.67225 0.24434 2.751 80 58.2 1.6 35.4±0.3 

700 2.1099 0.67874 3.108 101 74.1 4.5 40.0±0.2 

750 4.6088 1.4847 3.104 125 91.9 9.9 39.92±0.11 

800 5.3092 1.7032 3.117 157 94.5 11.4 40.08±0.11 

850 3.7568 1.2060 3.115 164 92.1 8.1 40.06±0.13

*900 2.9802 0.96075 3.102 156 93.8 6.4 39.89±0.12

*950 2.6491 0.85635 3.093 120 91.7 5.7 39.78±0.13

* 1,000 3.8378 1.2472 3.077 120 91.0 8.3 39.57±0.12

* 1,050 6.6500 2.1593 3.080 158 91.7 14.4 39.61 ±0.11

*1,150 10.867 3.5066 3.099 105 92.2 23.4 39.85±0.11

* 1,300 1.9346 0.62283 3.106 119 79.0 4.2 39.9±0.2

Total gas 3.071 39.50±0.12

Sample 88T38/11/DD12; ash-flow tuff; 97.7 mg biotite; measured 40Ar/36Ar=298.9; no plateau; preferred date=39.85±0.15 Ma; 

J-value=0.007100±0.25 percent (la); Iat41°10'6" N., long 114°56'59" W.

500

600

*700

*750

*800

*850

*900

*950

* 1,000

* 1,050

*1,150

* 1,300

0.46200

0.65700

5.0628

6.3761

4.1359

2.8251

2.2411

2.6114

5.9991

7.0790

4.9505

0.42176

Total gas

0.29833

0.26223

1.6003

2.0151

1.3108

0.8996

0.72269

0.83810

1.9146

2.2519

1.5710

0.13207

1.549

2.505

3.164

3.164

3.155

3.140

3.101

3.116

3.133

3.144

3.151

3.194

3.099

27

31

45

62

67

61

46

45

56

50

35

27

23.6

47.1

75.5

89.4

90.9

88.9

82.7

79.1

82.6

86.1

88.5

75.4

2.2

1.9

11.6

14.6

9.5

6.5

5.2

6.1

13.9

16.3

11.4

1.0

19.73±0.15

31.8±0.2

40.07±0.11

40.08±0.11

39.97±0.11

39.8±0.2

39.29±0.15

39.47±0.11

39.69±0.11

39.82±0.11

39.92±0.11

40.4±0.4

39.27±0.12

NORTHERN EAST HUMBOLDT RANGE

Sample 90B31B/42/DD28; ash-flow tuff; 62.3 mg biotite; measured 40Ar/36Ar=296.6; no plateau; minimum date=38.0±0.5 Ma;

J-value=0.007318±0.1 percent (1 a); lat 41 °2'50" N., long 115°4'10" W.

600 1.0729 0.48607 2.207 - 29.3 27.0 28.91 ±0.14

700 0.90034 0.32507 2.770 -- 32.2 18.0 36.20±0.16

*750 0.45053 0.15259 2.953 - 34.4 8.5 38.6±0.4

*800 0.29564 0.10106 2.925 -- 35.4 5.6 38.2±0.9

*850 0.17968 0.06158 2.918 - 38.4 3.4 38.1±0.5

*900 0.20100 0.07135 2.817 - 36.8 4.0 36.8±0.5

*950 0.30674 0.10802 2.840 - 35.8 6.0 37.1 ±0.6

* 1,000 0.40961 0.13985 2.929 -- 36.9 7.8 38.26±0.16

* 1,050 0.48513 0.16587 2.925 -- 39.3 9.2 38.2±0.4

*1,100 0.35793 0.12307 2.908 -- 41.7 6.8 38.0±0.4

*1,150 0.14697 0.04986 2.948 - 47.0 2.8 38.5±0.5

1,300 0.03581 0.01901 1.88 -- 27.4 1.1 25±3

Total gas 2.685 35.1 ±0.3
K26 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

Table 5. Abbreviated 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada 

volcanic field Continued.

Temperature

"ATR 39Ar/37Ar ATR (percent) ATK (percent)

Apparent age 

and error (Ma)

SOUTHERN EAST HUMBOLDT RANGE

Sample 91T12/67/DD33; dacite; 190.3 mg hornblende; measured 4()Ar/36Ar=296.6; plateau date=38.8±0.4 Ma; 

J-value=0.007750±0.1 percent (la); Iat40°42'll" N., long 115°4'22" W.

800

900

950

1,000

1,025

* 1,050

* 1,075

*1,100

*1,125

*1,150 

1,200 

1,250 

1,350

0.0241 

0.0081 

0.0089 

0.0430 

0.0892 

0.20204 

0.27813 

0.34620 

0.59076 

0.41827 

0.43733 

0.06277 

0.06355 

Total gas

0.0107

0.0058

0.0085

0.0139

0.0329

0.07275

0.10068

0.12429

0.20926

0.14800

0.15202

0.02121

0.02110

2.26

1.41

1.05

3.09

2.71

2.777

2.762

2.785

2.823

2.826

2.877

2.96

3.011

2.793

0.39

0.51

0.30

0.15

0.12

0.12

0.12

0.12

0.12

0.12

0.12

0.12

0.12

5.4

25.3

31.0

70.6

73.1

82.2

86.9

90.1

92.8

92.0

94.5

88.3

78.3

1.2

0.6

0.9

1.5

3.6

7.9

10.9

13.5

22.7

16.1

16.5

2.3

2.3

Sample 91T17/59/DD37; dacite; 268.3 mg hornblende; measured 40Ar/36Ar=296.6; plateau date=39.5±0.3 Ma; 

J-value=0.007482±0.1 percent (la); lat 40°40'4" N., long 115°6'22" W.

800 0.0133 0.0071 1.87 0.73 2.5 0.5

900 0.0167 0.0052 3.22 0.58 15.9 0.3

950 0.0038 0.0015 2.4 0.28 14.3 0.1

1,000 0.0062 0.0016 3.7 0.19 25.1 0.1

1,050 0.0150 0.0046 3.25 0.15 41.7 0.3

1,100 0.27736 0.09039 3.068 0.14 86.8 5.9

*1,125 0.59974 0.20398 2.940 0.14 89.3 13.4

*1,150 0.72717 0.24471 2.972 0.14 93.4 16.1

*U75 1.0586 0.35924 2.947 0.14 95.0 23.6

* 1,200 0.73829 0.24966 2.957 0.13 93.5 16.4

* 1,250 0.77600 0.26172 2.965 0.13 95.6 17.2

* 1,350 0.23507 0.07968 2.950 0.13 90.0 5.2

1,450 0.0397 0.0145 2.73 0.15 44.2 1.0

Total gas 2.957

31±3

20±2

15±8

43±4

37±2

38.4±0.4

38.2±0.4

38.5±0.5

39.0±0.3

39.1 ±0.3

39.8±0.4

41±2

41.6±0.8

38.6±0.8

25±5

43±7

33±24

50±35

43±10

41.0±0.6

39.2±0.4

39.67±0.14

39.34±0.11

39.5±0.2

39.6±0.3

39.4±0.6

37±4

39.5±0.4

Sample 91T19/68/DD37; dacite clast in conglomerate; 54.5 mg biotite; plateau date=40.98±0.10 Ma; measured 40Ar/36Ar=296.6; 

J-value=0.007818±0.1 percent (la); Iat40°41'48" N., long 115°4'44" W.

600

800

900

1,000

1,050

1,100

*1,150

*1,350

0.03695 

0.18778 

1.1766 

1.2428 

0.82265 

1.2821 

2.2633 

3.3878 

Total gas

0.01958

0.14897

0.42345

0.42579

0.28726

0.44795

0.77111

1.1517

1.89

1.260

2.778

2.919

2.864

2.862

2.935

2.942

2.829

13

19

98

87

57

56

63

31

18.5

20.7

71.5

84.3

80.0

81.9

91.9

95.2

0.5 

4.1

11.5

11.6

7.8

12.2

21.0

31.3

26±3

17.69±0.15

38.8±0.2

40.70±0.10

39.94±0.13

39.9±0.3

40.93±0.11

41.02±0.09

39.47±0.16
NORTHEAST NEVADA VOLCANIC FIELD K27

Table 5. Abbreviated 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada 

volcanic field Continued.

Temperature

"ATR 39Ar/37Ar AJR (percent) ATK (percent)

Apparent age 

and error (Ma)

WOOD HILLS

Sample 92BWH1/8/DD49; ash-flow tuff; 54.6 mg biotite; measured 40Ar/36Ar=298.9; no plateau; preferred date=39.7±0.1 Ma; 

J-value=0.007967±0.1 percent (la); Iat41°4'53" N., long 114°52'55" W.

600

700

750

800

850

900

950

1,000

1,050

1,100

1,150

* 1,200

* 1,350

0.05061

0.15604

0.19724

0.24367

0.45604

0.63587

1.1200

0.98496

1.2199

1.9483

3.0700

4.0152

4.7112

Total gas

0.02522

0.06264

0.07046

0.07927

0.15490

0.21578

0.39217

0.34639

0.43316

0.69260

1.0943

1.4337

1.6885

2.01

2.491

2.799

3.074

2.944

2.947

2.856

2.843

2.816

2.813

2.805

2.801

2.790

2.812

15

18

19

20

22

24

28

34

40

52

71

83

25

11.2

30.4

41.1

41.3

69.8

85.6

89.7

91.7

92.0

92.3

90.6

90.4

89.4

0.4

0.9

1.1

1.2

2.3

3.2

5.9

5.2

6.5

10.4

16.4

21.4

25.2

28.6±1.1

35.4±0.3

39.8±0.5

43.6±0.4

41.8±0.2

41.86±0.10

40.59±0.07

40.41 ±0.1 4

40.03±0.07

39.98±0.13

39.88±0.06

39.81 ±0.07

39.66±0.06

39.97±0.09

FERGUSON MOUNTAIN

Sample 12659-92T21/57/DD31; dacite; 307.3 mg hornblende; measured 40Ar/36Ar=298.9; plateau date=39.80±0.10 Ma; 

J-value=0.007656±0.1 percent (la); lat 40°26'15" N., long 114°8'54" W.

700

800

900

950

1,000

1,050

1,075

*1,100

*1,150

* 1,250

1,350

0.19505

0.17530

0.02904

0.02155

0.14291

1.1086

1.7045

1.2910

3.1788

1.2243

0.06718

Total gas

0.06734

0.06337

0.01411

0.01111

0.05322

0.38812

0.59050

0.44162

1.0922

0.42034

0.02097

2.90

2.77

2.06

1.94

2.69

2.86

2.887

2.923

2.911

2.913

3.20

2.889

2.5

1.4

0.41

0.34

0.19

0.16

0.16

0.16

0.16

0.16

0.18

33.4

20.9

10.9

11.1

44.0

70.3

79.3

87.0

80.9

80.4

80.8

2.1

2.0

0.4

0.4

1.7

12.3

18.7

14.0

34.5

13.3

0.7

39.6±0.3

37.8±0.7

28±5

27±6

37±1

39±1

39.43±0.07

39.93±0.06

39.76±0.06

39.8±0.2

44±2

39.5±0.2

DOLLY VARDEN MOUNTAINS

Sample 3233-92BDV/54/DD26; dacite; 48.2 mg biotite; measured 4"Ar/36Ar=298.9; plateau date=39.08±0.11 Ma; 

J-value=0.006182±0.25 percent (la); Iat40°19'20" N., long 114°31'9" W.

600

700

800

900

* 1,000

* 1,050

*1,100

*1,150

* 1,300

0.01061 

0.02629 

0.11411 

0.65604 

4.1651 

3.6756 

2.4423 

1.5050 

1.5808 

Total gas

0.00551

0.00771

0.02993

0.18019

1.1738

1.0403

0.68975

0.42405

0.44597

1.93

3.41

3.812

3.641

3.548

3-.S33

3.541

3.549

3.545

3.546

1.5

3.8

13

34

233

343

40

115

192

2.5

34.8

27.9

90.9

97.3

98.0

95.9

86.7

78.7

0.1

0.2

0.7

4.5

29.4

26.0

17.3

10.6

11.2

21 ±4 

.38±3 

42.0±0.9 

40.2±0.4 

39.14±0.11 

38.98±0.11 

39.06±0.11 

39.15±0.11 

39.10±0.11 

39.12±0.13
K28 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

Table 5. Abbreviated ^'A 

volcanic field Continued.

Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada

Temperature

"An, 39Ar/37Ar TR (percent) ' 9ArK (percent)

Apparent age 

and error (Ma)

SILVER ISLAND MOUNTAINS

Sample 91T3/60/DD37; andesite; 255.3 mg hornblende; measured 40Ar/36Ar=296.0; plateau date=42.6±0.3 Ma;

J-value=0.007595±0.1 percent (la); Iat40°49'59" 

800 0.11850 0.04696

900

925

950

1000

1025

1075

1,100

1,125

1,150

1,175

1,200

1,225

1,250

1,350

0.10432

0.02896

0.02547

0.00965

0.01097

0.02506

0.06174

0.26794

0.43486

0.96583

0.73636

0.32291

0.23418

0.37716

Total gas

0.03909

0.01029

0.00769

0.00427

0.00409

0.00936

0.01977

0.08724

0.13881

0.30592

0.23403

0.10260

0.07446

0.12065

N.,long 1] 

2.52

2.67

2.81

3.31

2.26

2.68

2.68

3.12

3.071

3.133

3.157

3.146

3.147

3.145

3.126

3.090

0.59

0.23

0.20

0.17

0.15

0.15

0.14

0.13

0.12

0.12

0.12

0.12

0.11

0.11

0.11

24.3

23.7

48.2

57.4

32.6

34.8

45.8

65.5

78.1

86.2

92.6

93.6

92.7

92.3

92.0

3.9

3.2

0.9

0.6

0.4

0.3

0.8

1.6

7.2

11.5

25.4

19.4

8.5

6.2

10.0

34±3

36±2

38±5

45±5

31±14

36±10

36±5

42±3

41.6±0.4

42.42±0.14

42.75±0.11

42.60±0.13

42.6±0.8

42.59±0.16

42.3±0.5

41.8±0.7

Sample 91T4/61/DD37; rhyolite; 70.8 mg biotite; measured 40Ar/36Ar=296.0; no plateau; excess 40Ar; preferred date=42.61±0.08 Ma; 

J-value=0.007803±0.1 percent (la); lat 40°49'56" N., long 113°57'24" W.

650

750

850

*950

* 1,000

1,050

1,100

1,150

1,350

0.20173

0.25269

0.76432

1.6035

2.3902

3.5278

3.2635

2.6182

0.73826

Total gas

0.09652

0.09054

0.24405

0.52348

0.78041

1.1321

1.0319

0.81507

0.22428

2.090

2.791

3.132

3.063

3.063

3.116

3.163

3.212

3.292

3.110

32

51

103

174

281

255

155

82

16

32.7

42.2

84.6

89.3

92.0

90.8

90.1

91.8

91.4

2.0

1.8

4.9

10.6

15.8

22.9

20.9

16.5

4.5

29.2±0.5

38.9±0.2

43.56±0.20

42.61 ±0.10

42.61 ±0.07

43.34±0.07

43.98±0.11

44.66±0.09

45.8±0.3

43.26±0.11

SANFORD SPRINGS

Sample 92B27/61/DD42; ash-flow tuff; 58.9 mg biotite; measured 40Ar/36Ar=298.9; plateau date=40.64±0.07 Ma; 

J-value=0.008156±0.1 percent (la); lat 39°48'39" N., long 114°7'55" W.

600

750

800

850

900

950

* 1,000

* 1,050

*1,100

*1,150

* 1,300

1.2902 

2.8101 

0.91643 

0.64531 

0.62326 

0.76540 

1.3234 

2.6291 

3.2377 

1.5480 

0.63725 

Total gas

0.49008

1.0077

0.32924

0.23191

0.22357

0.27660

0.47289

0.94023

1.1604

0.55418

0.22861

2.633

2.789

2.783

2.783

2.788

2.767

2.799

2.796

2.790

2.793

2.788

2.777

43

54

82

70

59

68

156

254

314

119

17

72.4

76.4

85.0

84.2

82.3

84.4

92.2

95.5

96.1

95.3

91.5

8.3

17.0

5.6

3.9

3.9

4.7

8.0

15.9

19.6

9.4

3.9

38.33±0.06 

40.57±0.35 

40.50±0.08 

40.48±0.23 

40.56±0.06 

40.26±0.15 

40.71 ±0.07 

40.68±0.06 

40.59+0.06 

40.64±0.07 

40.55±0.06 

40.40±0.12
NORTHEAST NEVADA VOLCANIC FIELD K29

Table 5. Abbreviated 40Ar/ 9Ar age-spectrum data for middle Eocene volcanic rocks from the central part of the Northeast Nevada 

volcanic field Continued.

Temperature

(°C) 40ArR

39ArK F39Ar/37Ar 40ArR (percent) 39AfK (percent)

Apparent age

and error (Ma)

GOLD HILL

Sample 91CP33/21/DD36; rhyolite;

J-value=0.005305±0.1 percent (la);

650 0.0415

750 0.2422

850 0.93339

950 1.2850

* 1,000 1.2874

* 1,050 1.9930

*1,100 1.7783

* 1,1 50 1.7706

* 1,350 0.52902

Total gas

48.6 mg biotite;

lat40°12'18"N.

0.0216

0.0597

0.22181

0.30511

0.30708

0.47635

0.42487

0.42515

0.12623

measured 40Ar/36Ar=298.0; plateau date=39.58±0.10 Ma;

, long 114°58'15" W.

1.92

4.059

4.208

4.211

4.192

4.184

4.185

4.165

4.191

4.161

3.7

19

123

149

168

140

66

78

24

13.5

49.2

86.0

89.3

90.0

92.9

92.5

93.9

83.1

0.9

2.5

9.4

12.9

13.0

20.1

17.9

18.0

5.3

18±2

38.4±0.3

39.83±0.06

39.86±0.07

39.7±0.2

39.60±0.11

39.62±0.06

39.42±0.07

39.67±0.06

39.42±0.13

Sample 91CP30/22/DD36; dacite; 242.4 mg hornblende; measured 40Ar/36Ar=296.6; plateau date=39.6±0.2 Ma;

J-value=0.005318±0.1 percent (la);

700 0.1485

800 0.03057

900 0.0189

1,000 0.04364

1,025 0.04991

1,050 0.20502

1,075 0.2893

*1,100 1.1110

*1,125 1.8807

* 1,1 50 0.02452

* 1,200 0.61772

1,350 0.11054

Total gas

lat40°ll'23"N.

0.02615

0.00907

0.00435

0.01074

0.01257

0.05046

0.0706

0.26461

0.45134

0.0586

0.14796

0.02693

, longll4°58'15"W.

5.68

3.37

4.35

4.06

3.97

4.063

4.099

4.199

4.167

4.180

4.175

4.10

4.192

0.62

0.31

0.31

0.23

0.18

0.16

0.16

0.15

0.15

0.15

0.15

0.13

27.2

34.8

48.5

53.0

70.4

82.8

87.0

93.7

95.8

91.5

95.4

83.2

2.3

0.8

0.4

0.9

1.1

4.5

6.2

23.3

39.8

5.2

13.1

2.4

54±2

32±1

41 ±4

39±3

38±3

38.6±0.5

38.9±0.5

39.8±0.2

39.54±0.08

39.7±0.4

39.6±0.2

39±2

39.8±0.4

COAL MINE CANYON

Sample 12624/56/DD31; ash-flow tuff; 267.4 mg hornblende;

J-value=0.007631±0.1 percent (la);

700 0.0287

800 0.0227

900 0.0321

950 0.04995

* 1,000 0.29047

* 1,025 0.95399

* 1,050 3.0453

* 1,1 00 2.7655

*1,150 0.65701

* 1,350 0.42209

Total gas

lat40°6'52"N.,

0.0085

0.00579

0.01020

0.01711

0.09773

0.32126

1.0264

0.92929

0.22110

0.14267

long 115

3.37

3.91

3.15

2.92

2.972

2.970

2.967

2.976

2.972

2.959

2.974

measured 40Ar/36Ar=298.9; plateau

°37'46" W.

0.64

0.55

0.20

0.16

0.16

0.16

0.16

0.16

0.15

0.14

2.5

14

39

52

64

80

91

94

87

79

date=40.4±0.2 Ma;

0.3

0.2

0.4

0.6

3.5

11.6

36.9

33.4

8.0

5.1

46±10

53±14

43±7

40±4

40.5±1.1

40.4±0.2

40.39±0.10

40.51 ±0.11

40.4±0.3

40.3±0.4

40.5±0.3
K30 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

Table 6. Production ratios for interfering isotopes of argon produced during irradiation. 

[Leaders (--) indicate not available]

Reactor 

package

DD9

DD12

DD26

DD28

DD31

DD33

DD36

DD37

DD42

DD49

Approx. error

(36Ar/37Ar)Ca

2.55x10"*

2.66x10"*

2.70x10"*

2.61x10"*

2.70x10"*

2.70x10^

..

2.80x10^

2.90x10"*

2.70x10"*

±0.01x10"*

(39Ar/37Ar)Ca

1.25xlQ-3

6.99x10"*

6.48x10"*

7.68x10"*

6.36x10"*

6.81X10"4

..

6.94x10^

6.30X10"4

5.95x10"*

±0.03x10"*

( 38Ar/37Ar)Ca

6.91xlQ-5

2.75x1 0"5

3.7x1 0"5

3.02x1 Q-5

3.17xlO"5

2.64x1 0-5

_

3.67xlO-5

2-llxlO-5

2.4x1 0'5

±0.2xlO~5

(4t'Ar/39Ar) K

1.26xlQ-2

9.07xlO~3

1.01 IxlO"2

8.78xlO"3

9.18xlO"3

9.76x1 0"3

__

8.99xlQ-3

7.5xlQ-3

7.8xlO"3

±0.4x1 0"3

(37Ar/39Ar) K

4.48x1 0"4

1.82x10"*

2.35x10^

8.30x1 Q-5

8.20xlO"5

l.lOxlO"4

._

1.49x10"*

9.9x1 Q-5

1.1x10"*

±0.6x10^

(38Ar/39Ar) K

1.30xlO~2

1.30xl(T2

1.31xlQ-2

1.306xl(T2

1.306xl(T2

1.307xlO~2

1.313xlO~2

1.318xlO"2

1. 306x1 0"2

±0.01 xlO'2
NORTHEAST NEVADA VOLCANIC FIELD K31

t; 7 o o

t:

<u "

O 1^

<u r^

602 § b

T3 rs 'o £

-2 'O

3 li*

KP

CO

<u S -=

-73 O OH

o ^-°

73 ^ *-

g C/J U

g 13 | 

P & «

&o o

P §

 H 8 g

o -2 'a,

DH C ^

H

_ OH

SB

- OH sis

CJ

,° O

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NORTHEAST NEVADA VOLCANIC FIELD K33

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scale 1:50,000. sensing data analysis for the Dolly Varden Mountains and

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Published in the Central Region, Denver, Colorado 

Manuscript approved for publication June 21, 1995 

Edited by Judith Stoeser

Graphics by Gayle M. Dumonceaux and the author 

Photocomposition by Gayle M. Dumonceaux

U.S. GOVERNMENT PRINTING OFFICE: 1996 - 774-045 / 20014 REGION NO. 8



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