44
Summary of Chemical Analyses and 40 Ar/ 39 Ar Age-Spectra Data for Eocene Volcanic Rocks from the Central Part of the Northeast Nevada Volcanic Field U.S. GEOLOGICAL SURVEY BULLETIN 1988-K ^^f^ff-^i: ^- p.;- :>-2?:>-"- '^. *> »:*is>: -*£*?.:*v* : :t?i*^'?>?t**:f. !

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Page 1: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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

^^f^ff-^i:^- p.;- :>-2?:>-"-

'^. *>»:*is>:-*£*?.:*v* ::t?i*^'?>?t**:f. !

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Page 3: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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

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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 ServicesBox 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-K1. 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

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CONTENTS

Abstract........................................................................................................................... KlIntroduction..................................................................................................................... 1Regional Eocene Setting................................................................................................. 1Data Tables and Plots of Analyses.................................................................................. 5References Cited............................................................................................................. 31

FIGURES

1. Map showing central part of Northeast Nevada volcanic field, composite stratigraphic column for NannyCreek 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................. 43. Geologic map of the Nanny Creek area, northern Pequop Mountains, Nevada.......................................................... 64. AFM ([Na2O+K2O]-FeO-MgO) diagrams for samples from the central part of the

Northeast Nevada volcanic field.................................................................................................................................. 75. Total-alkali (Na2O-t-K2O)-(SiO2) diagrams for samples from the central part of the

Northeast Nevada volcanic field.................................................................................................................................. 76. 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 Nevadaand adjacent Utah......................................................................_ K9

2. Chemical analyses of Eocene volcanic rocks from the Nanny Creek type area, Northeast Nevadavolcanic field......................................................................._ 10

3. Chemical analyses of other Eocene volcanic rocks from the central part of the Northeast Nevadavolcanic fi&d................................................................................................................................................^ 13

4. Summary of 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of theNortheast Nevada volcanic field................................................................................................................................. 22

5. Abbreviated 40Ar/39Ar age-spectrum data for middle Eocene volcanic rocks from the central part of theNortheast Nevada volcanic field.................................................................................................................................. 23

6. Production ratios for interfering isotopes of argon produced during irradiation......................................................... 307. U-Th-Pb isotopic ages of sphene from pyroxene diorite, southern East Humboldt Range,

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

ffl

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Summary of Chemical Analyses and40Ar/ 39Ar Age-Spectra Data for

Eocene Volcanic Rocks from theCentral 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 adja­ cent 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 vol­ canic rocks were known at a only few widespread sites in northeast Nevada and adjacent Utah (fig. IA, lettered local­ ities; 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 hav­ ing 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 Moun­ tains in central Nevada and west to the Snowstorm Moun­ tains 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

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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. Shad­ ed 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, Sche­ matic 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 indi­ cate tilted, bedded units, not true dip. No vertical scale implied.

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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 unconfor­ mity (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 andes­ itic 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 underly­ ing Paleozoic strata are shown schematically in figure 1C. A widespread basal sedimentary unit is included in the strati- graphic 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 discon­ tinuous 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

EXPLANATIONEOCENE 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 character­ ized 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 com- mun., 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).

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K4 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

NANNY CREEK NORTHERN EAST HUMBOLDT RANGE

APPARENT AGE (Ma)

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 I0 10 20 30 40 50 60 70 80 90 100

PERCENT 39Ar RELEASEDK

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

Tf JJ 88T41 (biotite) 39. 76 ±0.1 3 Ma

J ~~

88T38 (biotite) 39.85 ± 0.15 Ma

-

-Ill II0 10 20 30 40 50 60 70 80 90 100

PERCENT 39Ar RELEASEDK

LU 40

8LU 30

90B31B (biotite) 38.0 ± 0.5 Ma

0 10 20 30 40 50 60 70 80 90 100

PERCENT 39Ar, RELEASEDl\

SOUTHERN EAST HUMBOLDT RANGE50

40

30

20

50

i r

Lr 91T12 (hornblende) 38.8 ± 0.4 Ma

LU

40Q. 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 RELEASEDK

FERGUSON MOUNTAIN

APPARENT AGE 8 S

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 39ArK

(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)

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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 I10 20 30 40 50 60 70 80 90

PERCENT 39Ar, RELEASEDK

10

SILVER ISLAND MOUNTAINS

APPARENT AGE (Ma

3 fe 8 S

III 1 1 1 1 i I 1 1

fl- H^

btr:

91T3 (hornblende) 42.6 ± 0.3 Ma

H

91T4 (biotite) 42.61 ± 0.08 Ma

I I I I I I I0 10 20 30 40 50 60 70 80 90 100

PERCENT 39Ar RELEASED

SANFORD SPRINGSLU O < 401- Z LU CC <r rvi

1 1 1 1

92B27 (biotite) 40.64 ± 0.07 Ma

1 10 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 CANYON50

4012624 (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, north­ west 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-meta­ somatized 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 nomencla­ ture, and other major-element contents were little changed during metasomatism (Sawyer and others, 1989; Brooks and others, 1994). Because of their excessive K2O content, how­ ever, analyses from these potassium-metasomatized rocks commonly plot in the trachyandesite or trachydacite field on a total alkali-silica (TAS) diagram.

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K6 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

114°32'3D"

/ PHOTO' LINEAMENTS

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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

SOdo 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 North­ east Nevada volcanic field. B, Analyses from Nanny Creek type area.

12-

4HDacite n=92

54\ ' I r I ^ I ' I

58 62 66 70 74Si02, IN WEIGHT PERCENT

78

A

12-

4-

Rhyolite

n=24

54 581 ' I ^ 1 ' I 62 66 70 74

Si02, IN WEIGHT PERCENT78

B

Figure 5. Total-alkali (Na2O+K2O)-(SiO2) diagrams using re­ calculated 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 compo­ sitions 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 Tag- gait and others (1987). Trace element contents (tables 2, 3) were determined by energy-dispersive X-ray fluorescence

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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 4CM Hv

JS 36

Rhyolite

44 52 60 68 Si02, IN WEIGHT PERCENT

76

12

36 44 52 60 68 Si02, IN WEIGHT PERCENT

76

g 16occ.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 sam­ ples 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 Moun­ tains, Utah. /, Sanford Springs. J, Gold Hills area. K, Coal Mine Canyon, northern Adobe Range.

Page 15: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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)

37.337.538.438.838^339.639.941.842.5

Method

K-Ar, biotiteK-Ar, -K-Ar, biotiteK-Ar, biotiteK-Ar, -K-Ar, biotiteK-Ar, biotiteFission track, zirconK-Ar, biotite

Rock type

TuffDaciteAndesite-RhyoliteTuffRhyodacite-

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

9,036

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 cor­ rected 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 vol­ canic 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

Page 16: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 2

. C

hem

ical

ana

lyse

s of

Eoc

ene

volc

anic

roc

ks f

rom

the

Nan

ny C

reek

type

are

a, N

orth

east

Nev

ada

volc

anic

fie

ld.

[Loc

atio

n of

are

as s

how

n in

fig

ure

IA.

Maj

or o

xide

s (w

eigh

t per

cent

, unc

orre

cted

) de

term

ined

by

X-r

ay s

pect

rosc

opy;

ana

lyst

s D

.F.

Siem

s an

d J.

E. T

agga

rt; F

eTO

s in

dica

tes

tota

l iro

n re

port

ed a

s

erro

r is

10

perc

ent o

f val

ue l

iste

d or

±6

(Rb)

, ±5

(Sr)

, ±4

(Y),

±3 (

Zr),

±3 (

Nb)

, and

±10

(B

a), w

hich

ever

is g

reat

er.

Ast

eris

k (*

) in

dica

tes

date

d sa

mpl

e (t

able

4).

Map

uni

t des

igna

tions

as

infig

ure

3]

Map

uni

t

Lab

No.

Fiel

d N

o.

----

--L

atitu

de -

Lon

gitu

de

Tl

D-3

2363

4Q

QT

<

A*

oo

l jo

*41

°01'

30"N

.11

4°32

'47"

W.

Tl

D-3

6520

490

B6

41°0

1'38

"N.

114°

32'5

4"W

.

Tl

D-3

6520

590

B11

41°0

0'34

"N.

114°

32'0

5"W

.

T2D

-323

633

CO

T C

C=|

co

o 1

OJ

41°0

1'29

"N.

114°

32'4

1"W

.

T2D

-365

206

90B

341

°00'

42"N

.11

4°32

'27"

W.

T2D

-365

207

Qnr

>7

Ay\

)D /

/\

41°0

1'38

"N.

114°

32'4

5"W

.

T2D

-365

208

Qrv

DT

Oy\J

D I

D41

°01'

38"N

.11

4°32

'45"

W.

T2D

-365

209

90B

1241

°00'

57"N

.11

4°32

'30"

W.

Maj

or-o

xide

com

posi

tion

SiO

2A

120

3Fe

TO

3M

gOC

aON

a2O

K20

TiO

2P2

05

MnO

LOI

Tot

al

71.4

14.2 1.78

0.53

2.29

3.18

4.14

0.37

0.11

0.02

0.96

99.9

8

67.6

16.6 1.80

0.66

2.75

3.81

4.13

0.45

0.14

0.02

1.48

99.4

4

67.3

15.6 2.57

0.60

2.54

3.46

4.09

0.39

0.14

0.02

2.41

99.1

2

78.0

11.6 0.45

0.12

0.76

2.46

5.36

0.1

0.05

0.02

0.67

99.5

9

75.0

12.8 0.93

0.29

0.88

3.08

5.12

0.10

0.05

0.04

1.25

99.5

4

76.5

11.6 0.74

0.24

0.87

2.52

5.29

0.09

0.07

0.02

1.01

98.9

5

75.2

11.4 1.74

0.21

0.78

2.39

5.40

0.09

0.05

0.02

1.65

98.9

3

77.7

10.5 1.03

0.18

0.85

2.21

4.48

0.11

0.05

0.02

1.96

99.0

9T

race

ele

men

t com

posi

tion

Rb

Sr Y Zr Nb

Ba

114

408 21 212 8

1,97

4

144

598 20 276 15

2,11

0

157

573 24 252 12

2,55

0

152

109 18 99 12

605

201

163 22 141 15

1,04

3

203

154 25 120 14 915

251

130 23 114 11 711

154

138 21 112 12

967

ss o

r ra ^3 » CO tfl

>

00 a o CO C/3

§

Page 17: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 2

. C

hem

ical

ana

lyse

s of

Eoc

ene

volc

anic

roc

ks f

rom

the

Nan

ny C

reek

type

are

a, N

orth

east

Nev

ada

volc

anic

fie

ld C

onti

nued

Map

Uni

t

T ah N

r>\-

id\)

1N

U.

Fiel

d N

o.

Lat

itude

-

Lon

gitu

de

T2

D-3

6521

090

B13

41°0

1'55

"N.

114°

32'3

9"W

.

T3x

D-3

6521

990

B5

41°0

1'07

"N.

114°

32'2

5"W

.

T3x

D-3

6522

0Q

OR

1QA

:7\J

LJ

1 7 r\

41°0

1'23

"N.

114°

31'4

0"W

.

T3x

T~\

O

/C

C-"

>^

1D

-36

52

21

41°0

1'23

"N.

114°

31'4

0"W

.

T3x

D 3

5705

5Q

OR

'MA

y\J

Lj £.^

r\

41°0

1'28

"N.

114°

32'3

0"W

.

T3x

D-3

5705

690

B24

B41

°01'

28"N

.11

4°32

'30"

W.

T3x

D

5033

5991

T10

*41

°03'

02"N

.11

4°30

'10"

W.

T3a

D-3

6521

1

41°0

1'34

"N.

114°

32'3

6"W

.

Maj

or-o

xide

com

posi

tion

SiO

2A

120

3Fe

TO

3M

gOC

aON

a2O

K2O

TiO

2P

2O5

MnO

LOI

Tota

l

75.2

12.4 1.15

0.19

0.89

3.04

4.85

0.10

0.05

0.02

1.55

99.4

4

61.3

16.3 4.89

2.54

5.59

3.52

2.09

0.59

0.19

0.07

2.66

99.7

4

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

99.5

8

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

61.7

16.4 4.46

2.28

4.74

3.37

2.88 .5

60.

230.

082.

2298

.92

68.5

12.6 1.39

0.96

2.30

2.12

2.34

0.16

0.05

0.02

9.17

99.6

1T

race

ele

men

t com

posi

tion

Rb

Sr Y Zr Nb

Ba

208

157 20 126 14

952

62 525 18 168 7

1,34

8

54 544 22 154 12

1,13

6

65 509 24 147 8

1,46

2

81 574 21 181 9

1,24

0

95 552 18 171 7

1,24

3

73 526 20 124 10

2,91

0

104

535 16 146 13

1,33

6

z S £ >

on

H Z ra i > o

r

n >

z n Tl

Page 18: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 2

. C

hem

ical

ana

lyse

s of

Eoc

ene

volc

anic

roc

ks f

rom

the

Nan

ny C

reek

type

are

a, N

orth

east

Nev

ada

volc

anic

fie

ld C

onti

nued

Map

Un

it -

Lab

No.

Fiel

d N

o.

Lat

itude

-

Lon

gitu

de --

---

T3a

D-3

5705

490

B9B

*41

°01'

34"N

.11

4°32

'36"

W.

T3a

T~\

O

/^C

O 1

OU

365

212

90B

1041

°01'

36"N

.11

4°32

'08"

W.

T3a

D-3

6521

3nr\

r> 1

1yu

m /

41°0

1'56

"N.

114°

32'2

5"W

.

T3a

D-3

6521

490

B20

41°0

1'33

"N.

H4°

31'4

4"W

.

T3a

D-3

6521

590

B25

41°0

3'03

"N.

114°

31'4

3"W

.

T3a

DO

/^C

T 1

O 3

652 I

S

90B

2741°0

2'1

0"N

.

T4

D-3

6521

690

B26

A41

°02'

04"N

.11

4°30

'52"

W.

T4

D 3

6521

790

B26

B41

°02'

04"N

.11

4°30

'52"

W.

Maj

or-o

xide

com

posi

tion

SiO

2A1

203

FeT

O3

MgO

CaO

Na2

OK

2OTi

O2

P20

5M

nOLO

ITo

tal

74.8

12.5 1.35

0.23

0.89

2.86

5.16

0.10

0.05

0.02

1.65

99.6

1

73.8

11.3 1.16

0.51

1.38

1.44

4.93

0.15

0.06

0.02

4.69

99.4

4

76.0

11.8 0.67

0.17

0.96

2.62

5.02

0.11

0.05

0.02

1.69

99.1

1

79.0

10.2 0.34

0.10

0.12

1.21

7.12

0.08

0.05

0.02

1.27

99.5

1

75.7

11.1 1.12

0.22

0.74

1.64

6.55

0.13

0.14

0.02

1.74

99.1

0

68.4

13.3 2.07

0.79

1.80

2.26

4.05

0.10

0.08

0.04

6.90

99.7

9

70.2

14.3 2.71

0.89

3.00

3.46

2.99

0.30

0.13

0.03

1.35

99.3

6

70.5

14.3 2.69

0.61

3.05

3.48

3.07

0.32

0.16

0.03

0.99

99.2

0T

race

ele

men

t com

posi

tion

Rb

Sr Y Zr

Nb

Ba

205

143 22 128 12 773

115

480 18 149 14

1,94

1

177

176 18 143 17

1,14

6

183 79 14 121 11 895

200

153 21 146 11

1,49

9

146

246 16 110 13

1,65

8

110

450 17 133 9

1,46

8

111

441 13 136 9

1,53

5

tfl i H GO

0 ra 90 co GO

00 Cfl

oo O

90

Cfl w GO 3

Page 19: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

ic r

ocks

fro

m th

e ce

ntra

l pa

rt o

f the

Nor

thea

st N

evad

a vo

lcan

ic f

ield

.[L

ocat

ion

of a

reas

sho

wn

in f

igur

e IA

. M

ajor

oxi

des

(wei

ght p

erce

nt, u

ncor

rect

ed)

dete

rmin

ed b

y X

-ray

spe

ctro

scop

y; a

naly

sts

D.F

. Si

ems,

J.S

. M

ee, a

nd I

.E.

Tag

gart

; FeT

Cb

indi

cate

s to

tal

iron

re

port

ed a

s Fe

2C>3

. L

OI

(wei

ght p

erce

nt),

loss

on

igni

tion

at 9

25°C

. R

b, S

r, Y

, Zr,

and

Nb

(par

ts p

er m

illio

n) d

eter

min

ed b

y en

ergy

-dis

pers

ive

anal

ysis

, 10

9Cd

and

241A

m s

ourc

es;

anal

ysts

E.J

. L

aRoc

k an

d K

. Woo

dbur

ne; e

rror

is 1

0 pe

rcen

t of v

alue

list

ed o

r ±6

(R

b), ±

5 (S

r), ±

4 (Y

), ±3

(Zr

), an

d ±3

(N

b), w

hich

ever

is g

reat

er.

Ast

eris

k (*

) in

dica

tes

date

d sa

mpl

e (t

able

4);

§ in

dica

tes

pyro

xene

dio

rite

(ta

ble

7); t

indi

cate

s sa

mpl

e re

ceiv

ed f

rom

K. M

uelle

r, U

nive

rsity

of W

yom

ing;

tt

indi

cate

s sa

mpl

e re

ceiv

ed f

rom

P. C

amill

eri,

Uni

vive

rsity

of W

yom

ing]

Loc

ality

-

Fiel

d N

o.

Lab

No.

Lat

itud

e- - -

Lon

gitu

de -

Sout

hern

Sna

ke M

ount

ains

QQ

T

1 1

OO

111

D-3

2362

041

°07'

35"N

.11

4°59

'08"

W.

OQ

T

'J /

£*

oo 1

36*

r\

^ ">

'j /£ "

> 1

L)

j 23

621

41°0

9'57

"N.

114°

57'0

6"W

.

QQ

T

~11

001

J 1

V\

OT

5/C

T">

D 3

2362

241°1

0'0

2"N

.11

4°57

'02"

W.

QQ

T 1

0*

OO

1

JO

D 3

2362

341

° 1 O

WN

.11

4°56

'59"

W.

OQT

39

D-3

2362

441

°12'

03"N

.H

4°54

'04"

W.

QQ

T /in

001

ft\}

D'J

T2

/^T

C 3

2362

5 41

°12'

04"N

.11

4°54

'21"

W.

88T4

1*r\

m

/^*")

/^u

323

626

41°1

2'04

"N.

114°

54'3

6"W

.

88T

42*

D'J

TJ /£T

7 3

23

62

7

41°1

2'0

2"N

.H

4°5

4'4

3"W

.

Maj

or-o

xide

com

posi

tion

SiO

2A1

203

FeT

O3

MgO

CaO

Na2

OK

2OT

iO2

P20

5M

nOLO

IT

otal

68.0

11.6 3.01

0.76

1.59

1.09

4.65

0.41

<0.0

5<0

.02

8.45

100.

43

81.7 8.63

0.66

0.11

0.30

0.83

6.25

0.08

0.06

<0.0

20.

6999

.33

61.9

16.4 5.67

1.57

3.66

3.89

3.91

0.55

0.16

<0.0

22.

2499

.97

77.1

11.2 1.39

0.11

0.23

0.53

6.77

0.11

0.13

0.04

1.72

99.3

3

75.6

12.1 1.61

<0.1

01.

072.

815.

030.

340.

07<0

.02

0.48

99.2

3

62.1

17.6 5.06

0.67

4.19

3.93

3.41

0.77

0.31

0.03

1.57

99.6

4

79.3 9.83

0.43

0.21

0.40

0.93

6.69

0.11

0.18

<0.0

21.

2199

.31

64.4

14.6 5.41

0.86

1.86

1.86

6.16

0.61

0.24

0.03

3.35

99.3

8T

race

ele

men

t com

posi

tion

Rb

Sr Y Zr

Nb

Ba

221

170 52 464

*37

1,28

8

131 54 8 82 9

836

89 303 11 121 6

860

117 40 13 114 13 837

134

139 34 408 20

1,97

5

94 450 19 157 9

1,21

6

168 60 23 91 6

876

172

262 26 130 7

1,53

7

s

ra

> C/3 H a o

r

n n

Page 20: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

ic r

ocks

fro

m th

e ce

ntra

l par

t of

the

Nor

thea

st N

evad

a vo

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ield

Con

tinu

ed.

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ality

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o.

I

nK

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itude

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gitu

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ther

n E

ast H

urab

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.

90B

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35

7058

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"N.

115°

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.

91T1

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360

40°4

2'09

" N

.11

5°04

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91T

12*

D-5

0336

140

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.11

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W.

Sout

hern

Eas

t Hur

abol

dt R

ange

91T

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-503

362

40°4

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.

91T1

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50

3363

40°4

0'10

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115°

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.

91T

15D

-503

364

40°3

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" N

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W.

91T

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D-5

0336

5 4

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115°

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.

Maj

or-o

xide

com

posi

tion

SiO

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FeT

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otal

62.0

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1.80

4.48

4.45

1.64

0.69

0.19

0.08

2.62

99.9

7

65.4

14.2 3.85

1.37

3.49

1.53

2.32

0.39

0.15

0.02

6.67

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9

61.7

16.0 4.92

1.77

3.74

3.46

2.94

0.61

0.17

0.06

3.45

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2

61.1

16.3 5.12

2.77

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1.26

0.62

0.17

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2.77

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3.11

5.66

3.58

1.84

0.70

0.19

0.12

1.59

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8

59.0

16.7 5.68

3.53

6.06

3.50

2.10

0.83

0.24

0.11

1.45

99.2

66.1

15.9 2.96

0.85

2.79

3.47

3.36

0.40

0.16

0.04

3.28

99.3

1

63.8

15.5 3.77

1.72

4.12

3.06

3.29

0.47

0.14

0.05

3.09

99.0

1T

race

ele

men

t com

posi

tion

Rb

Sr Y Zr Nb

Ba

43 481 16 158 5

1,08

3

114

2,96

5 12 194 10

2,23

9

77 341 18 140 12

1,28

6

70 404 11 139 11

1,23

5

80 402 17 122 15

1,16

8

84 653 18 133 8

1,54

4

95 320 12 160 12

1,52

7

80 359 16 112 10

1,31

7

o "d c«

ra

a 2 ra 2 H CO > 00 o H

CO 00 §

Page 21: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

ic r

ocks

fro

m th

e ce

ntra

l par

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orth

east

Nev

ada

volc

anic

fie

ld C

onti

nued

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Loca

lity

Fiel

d N

o.

Lab

No.

-

Lat

itude

Lon

gitu

de ~

Sout

hern

Eas

t Hum

bold

t Ran

ee91

T19

*D

-503

366

40°4

1'48

" N

.H

5°04

'44"

W.

91T2

0D

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367

40°4

1'22

" N

115°

05'2

2" W

.

91T2

2§D

-503

368

40°3

8'33

" N

.

115°

05'2

8" W

.

91T

23D

503

369

40°3

8'29

" N

.

115°

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5" W

.

92B

42D

-522

594

40°4

1'33

" N

.

115°

04'3

3" W

.

92B

45D

-522

595

40°4

1'39

" N

.

115°

03'5

0" W

.

92B

46D

-522

596

40°4

1'23

" N

.11

5°05

'15"

W.

92B

49D

CT

TC

QO

jZ

ZjV

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NT-

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.

115°

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.M

ajor

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de c

ompo

sitio

n

SiO

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203

FcTO

3M

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TiO

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O5

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al

71.4

12.4 2.00

0.88

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4.10

0.39

0.14

0.05

2.25

98.7

1

67.5

13.8 1.44

0.72

3.06

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6.81

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6

53.2

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1.38

0.45

0.27

0.08

0.76

98.8

3

58.4

17.0 5.91

2.48

5.30

3.56

2.32

0.81

0.24

0.07

3.18

99.2

7

67.3

12.6 1.55

1.05

2.66

0.67

4.09

0.19

0.11

0.02

8.80

99.0

4

62.8

15.7 4.29

2.20

2.88

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0.68

0.19

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8

72.8

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0.15

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1

64.3

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1.60

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0.46

0.18

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3.25

99.2

Tra

ce e

lem

ent c

ompo

sitio

nR

bSr Y Z

r Nb

Ba

89 509 13 160 11

1,94

1

571,

101 10 74 10

1,47

4

351,

948 11 84 4

696

50 554 19 120 10

1,50

5

126

763 18 129 9

1,26

1

106

277 12 94 6

1,11

2

138

137 18 63 12

1,17

5

46 932 15 129 8

1,30

3

H ffi

m

> GO H

Z m O R o O

Page 22: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

ic r

ocks

fro

m th

e ce

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57

D 5

2259

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.11

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rea

HI

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6519

241

°15'

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114°

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0"W

.

H2

D-3

6519

341

°15'

N.

114°

37'3

0"W

.

H3

D-3

6519

441

°15'

N.

114°

37'3

0"W

.

H4

D-3

6519

541

°15'

N.

114°

37'3

0"W

.

H6

D-3

6519

641

°15'

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114°

37'3

0"W

.

we

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6519

741

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f D

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198

41°1

4'36

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114°

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.

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SiO

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203

FeTO

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al

65.2

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62.4

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6

74.9

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14.6 4.15

0.78

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7

78.1

11.1 0.84

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3

62.5

17.9 4.46

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4

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99.5

3T

race

ele

men

t com

posi

tion

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Sr Y Zr

Nb

Ba

106

298 22 139 15

988

75 494 21 190 11

1,75

4

167

266 23 141 15

1,61

1

137

343 21 197 12

1,72

1

118

226 27 118 16

1,11

5

17 296 14 105 15 650

138

482 23 253 9

1,87

3

72 499 22 195 12

1,48

5

ON O r o n GO m

o §

m Cd

> GO m

o Cd

> GO

Page 23: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

ic r

ocks

fro

m th

e ce

ntra

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o.

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itude

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199

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4'48

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.

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6'28

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1 14°

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.

Dea

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2fD

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201

41°1

7'18

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.

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ills

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41°1

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.

on

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j

41°1

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114°

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.

92B

WH

l*tt

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2259

041

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.11

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nT

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JO 4

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yzrJ

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586

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.

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com

posi

tion

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MnO

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12.7 1.13

0.38

0.57

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1.86

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5

70.7

12.1 1.16

0.58

1.40

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2

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1

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11.8 2.97

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3.81

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15.7 2.74

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3.65

4.92

0.40

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1.04

99.2

75.2

12.6 1.44

0.19

0.91

3.15

4.86

0.15

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2

63.5

16.8 4.75

0.68

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1.71

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64.9

15.4 4.36

1.76

4.21

2.81

3.40

0.57

0.18

0.08

1.99

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6T

race

ele

men

t com

posi

tion

Rb

Sr Y Zr

Nb

Ba

176

217 21 139 18

1,59

6

191

809 17 146 12

1,19

5

133

634 23 157 13

1,81

0

143

490 21 162 10

1,39

4

165

519 28 278 15

2,09

6

140

125 14 113 13

1,27

4

70 384 16 136 8

1,04

3

110

259 26 199 16

1,09

6

ffi m

> GO O

r

o o 33

m

r

o

Page 24: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

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fro

m th

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ntra

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ality

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o.

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ly V

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ount

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"N.

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.

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er I

slan

d M

ount

ains

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3*D

503

357

40°4

9'59

" N

.11

3°56

'49"

W.

91T4

*D

503

358

40°4

9'56

" N

.11

3°57

'24"

W.

91T

30D

503

370

39°4

8'26

" N

.11

4°08

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ord

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gs a

rea,

sou

ther

n D

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ek M

ount

ains

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32D

503

371

39°4

8'23

" N

114°

08'1

5"W

.

91T3

3D

-5Q

3372

39°4

8'35

" N

.11

4°08

'25"

W.

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13D

-516

488

114°

10'4

7"W

.

92B

14D

51

6489

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or-o

xide

com

posi

tion

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2A

120

3Fe

TO3

MgO

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Na2

OK

2OT

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P2O

5M

nOLO

IT

otal

64.1

15.2 4.46

2.04

3.74

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0.55

0.15

0.06

3.16

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3

59.2

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2.79

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4

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14.9 2.31

0.88

2.99

3.15

2.84

0.21

0.11

0.07

3.53

98.9

9

60.8

15.9 5.56

3.71

5.73

3.38

2.55

0.78

0.20

0.08

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99.5

59.8

16.0 5.31

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0.76

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1.41

98.9

1

60.0

16.0 5.44

3.61

5.84

2.76

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99.3

7

66.0

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4.71

0.50

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2.97

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1.69

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Rb

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Ba

109

230 24 182 19

977

67 368 19 132 10

1,04

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84 275 9

122 15

1,04

5

83 490 30 194 15

1,14

3

94 513 21 190 13

1,19

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75 463 24 174 5

979

189

331 32 234 18

1,16

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168

383 21 202 11

1,23

4

m o

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H o

o T1 GO m D § H da > GO z GO 00 H m O m H

dd GO 5

Page 25: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

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ount

ains

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OO

13 1

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.

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6485

39°5

7'43

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114°

06'4

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.

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21D

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6491

39°5

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.

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6486

39°5

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W.

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27*

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.

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66.4

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1.54

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60.9

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3.78

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0.20

0.09

0.80

99.3

5Tr

ace

elem

ent c

ompo

sitio

nR

bSr Y Z

r Nb

Ba

198

269 27 205 21

1,24

5

206

281 23 210 21

1,23

9

194

255 26 197 18

1,20

8

167

350 21 201 16

1,57

6

206

276 25 218 20

1,14

1

241

157 22 192 22 981

78 373 14 114 8

1,34

3

77 474 20 186 13

1,12

6

H

ffi m

> GO H

Z ra O

r

o o

Page 26: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

ic r

ocks

fro

m th

e ce

ntra

l par

t of t

he N

orth

east

Nev

ada

volc

anic

fie

ld C

onti

nued

.to o

Loca

lity -

Fiel

d N

o.

Lab

No.

Sanf

ord

Sori

nes

area

, sou

ther

n D

eeo

Cre

ek M

ount

ains

92B

33

D-5

164

97

39°4

8'09

" N

. 11

4°07

'50"

W.

92B

34

D-5

164

96

39°4

8'16

"N.

H4°

07'4

4"W

.

92B

38

D-5

164

99

39°4

9'29

" N

. 11

4°07

'31"

W.

92B

60

D 5

1649

2 39

°59'

20"

N.

114°

08'0

4"W

.

92B

62

D-5

164

93

39°5

2'30

" N

. 11

4°10

'37"

W.

92B

69

D-5

164

94

39°5

1'39

"N.

114°

09'4

9"W

.

92B

70

D-5

164

82

39°5

1'40

"N.

114°

09'5

3"W

.

92B

71

D-5

1648

3 39

°51'

10"N

. 11

4°08

'01"

W.

Maj

or-o

xide

com

posi

tion

SiO

2 A1

203

FeTO

3 M

gO

CaO

Na2

O

K^O

Ti0

2 P2

05

MnO

LOI

Tot

al

62.8

15

.9

4.11

2.

66

4.63

3.16

2.

860.

61

0.19

0.

072.

3899

.37

60.7

16

.1

4.86

3.

01

5.37

2.81

2.

830.

72

0.20

0.

082.

9699

.64

67.4

11

.1

1.42

1.

12

5.00

1.35

3.

060.

20

0.11

0.

028.

4899

.26

64.5

14

.3

5.05

1.

93

3.88

2.80

4.

460.

55

0.23

0.

091.

3699

.15

65.0

14

.6 4.45

1.

06

3.72

2.93

4.

820.

51

0.18

0.

091.

4998

.85

65.0

14

.9

4.51

2.

65

4.14

3.02

3.

430.

73

0.19

0.

070.

5599

.19

70.8

13

.9

2.07

0.

53

2.34

3.07

4.

900.

37

0.25

0.

050.

7999

.07

62.5

15

.5

4.28

2.

69

4.92

2.95

3.

140.

64

0.20

0.

072.

2399

.12

Tra

ce e

lem

ent c

ompo

sitio

nR

bSr Y Z

rN

bB

a

91 513 15 182 16

1,28

8

76 475 24 165 10 827

60 637 13 93 12

1,76

1

195

226 26 198 24

1,13

8

191

284 31 210 16

1,27

7

136

383 23 225 15

1,16

2

194

224 24 213 21 423

92 481 17 198 14

1,27

1

o

r o Tl

GO m

o §

w da > GO m

> GO H m o H

Cd

Page 27: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

Tab

le 3

. C

hem

ical

ana

lyse

s of

oth

er E

ocen

e vo

lcan

ic r

ocks

fro

m th

e ce

ntra

l par

t of t

he N

orth

east

Nev

ada

volc

anic

fie

ld C

onti

nued

.

Loc

ality

Fi

eld

No

.

Lab

No.

-

Sanf

ord

Spri

ngs

area

92B

67

D-5

165

00

39°4

8'15

"N.

Gol

d H

ill a

rea

91C

P30*

D

-522

592

40°1

1'23

"N.

114°

58'1

5"W

.

91C

P33*

D

-522

593

40°1

2'18

"N.

114°

58'1

5"W

.

Coa

l Min

e C

anyo

n12

247

D-5

5906

2 41

°07'

N.

115°

37'5

7"W

.

1262

4*

D

5590

63

41°0

6'52

"N.

115°

37'4

6"W

.

Maj

or-o

xide

com

posi

tion

SiO

^A1

203

FeTO

3 M

gO

CaO

Na2

0

K2O

P2O

5M

nOLO

IT

otal

65.6

12.6

1.

62

1.81

5.

882.

58

2.44

0.

220.

120.

036.

2399

.13

62.2

15.8

5.

16

2.68

5.

192.

82

2.73

0.

630.

150.

12.

0699

.52

68.5

15.0

1.

68

0.72

2.

472.

87

3.95

0.

330.

120.

052.

9398

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65.7

15.4

3.

46

1.04

2.

922.

61

5.16

0.

670.

230.

041.

7999

.02

65.6

15.2

3.

54

1.17

3.

112.

58

4.85

0.

650.

230.

082.

3999

.4T

race

ele

men

t co

mpo

sitio

n

Rb Sr Y Zr Nb

Ba

85 412 17 111 9

1,37

3

115

279 29 191 15 931

115

206 36 209 16

980

130

366 16 157 16

2,25

2

138

372 20 164 15

1,52

7

on H 1 O R >

2! o r

D

Page 28: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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 Nevadavolcanic field.[Location of areas shown in figure \A. Ferguson Mountain sampled by J. Welsh for 40Ar/39Ar date, (12659), resampled by C. Thorman for rockchemistry (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 CreekNanny CreekNanny CreekNanny CreekSouthern Snake MountainsSouthern Snake Mountains

Southern Snake MountainsSouthern Snake Mountains

Northern East Humboldt Range

Southern East Humboldt RangeSouthern East Humboldt RangeSouthern East Humboldt RangeDeadman Creek Area,

Windermere Hills2Deadman Creek Area,

Windermere Hills2Wood Hills

Ferguson MountainDolly Varden MountainsSilver Island MountainsSilver Island MountainsSanford SpringsGold HillGold Hill

Coal Mine Canyon

Sample no.

91T1090B9B88T5588T5688T3688T42

88T4188T38

90B31B

91T1291T1791T19WC-6

WC-1

92BWH1

12659-92T213233-92BDV91T391T492B2791CP3393CP30

12624

Rock type

DaciteAsh-flow tuffAsh-flow tuffAsh-flow tuffAsh-flow tuffDacite

Ash-flow tuffAsh-flow tuff

Ash-flow tuff

DaciteDaciteDacite 1Dacite

Ash-flow tuff

Ash-flow tuff

DaciteDaciteAndesiteRhyoliteAsh-flow tuffRhyoliteDacite

Ash-flow tuff

Apparent age (Ma) Mineral and error (la) Character of spectrum

HornblendeBiotiteBiotiteBiotiteBiotiteBiotite

BiotiteBiotite

Biotite

HornblendeHornblendeBiotiteHornblende

Biotite

Biotite

HornblendeBiotiteHornblendeBiotiteBiotiteBiotiteHornblende

Hornblende

39.23±0.539.61±0.1339.89+0.1241.08+0.1139.5±0.239.7±0.1

39.76±0.1339.85±0.15

38.0±0.5

38.8+0.439.5+0.340.98±0.139.87±0.1

40.38±0.1

39.7±0.1

39.80±0.139.08±0.1142.6±0.342.61±0.840.64+0.0739.58±0.1039.6±0.2

40.4±0.2

Plateau date; 87 percent of total 39ArKPlateau date; 60 percent of total 39ArKPlateau date; 94 percent of total 39ArKPlateau date; 86 percent of total 39ArKPlateau date; 95 percent of total 39ArKPreferred date for disturbed spectrum;60 percent of total 39ArKPlateau date; 63 percent of total 39ArKPreferred date for disturbed spectrum;80 percent of total 39ArKPreferred date for disturbed spectrum;54 percent of total 39ArK ; probably aminimumPlateau date; 71 percent of total 39ArKPlateau date; 92 percent of total 39ArKPlateau date; 52 percent of total 39ArKPlateau date; 77 percent of total 39ArK

Plateau date; 64 percent of total 39ArK

Preferred date for disturbed spectrum;excess argon, maximum estimatePlateau date; 62 percent of total 39ArKPlateau date; 94 percent of total 39ArKPlateau date; 81 percent of total 39ArKPreferred date for disturbed spectrumPlateau date; 92 percent of total 39ArKPlateau date; 74 percent of total 39ArKPlateau date; 63 percent of total 39ArK(recalculated)Plateau date; 93 percent of total 39ArK

'Dacite clast in basal conglomerate. 2Mueller, (1992).

Page 29: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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]

Temperature4°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);

800900

1,0001,050

*1,100*1,150*1,175* 1,200* 1,250

1,350

0.129800.021390.019920.037790.112081.23231.72750.591570.971290.54260

plateau date=39.23±0.5 Ma;lat 41°1'28" N., long 1 14°30'10" W.0.042910.007100.009490.009770.039660.435260.613770.207500.344040.18741

Total gas

Sample 90B9B/32/DD28; ash-flow tuff; 58 mg biotiteJ-value=0.007317±0.1 percent (la);

650750850900950

1,0001,050

*1,100*1,150* 1,300

0.019820.060420.378700.853690.630851.44161.30491.64313.36232.1992

3.025 2.53.01 1.102.10 0.413.87 0.342.82 0.202.831 0.152.815 0.152.851 0.152.823 0.152.895 0.152.839

; measured 40Ar/36Ar=296.6

23.220.927.461.865.285.893.288.292.893.6

2.30.40.50.52.1

22.932.410.918.19.9

42±142±829±754±539±239.3±0.239.08±0.1139.6±0.439.2±0.240.2±0.539.4±0.3

; plateau date=39.61±0.13 Ma;lat 41°1'23"N., long 114°31'40"W.0.020230.039480.129200.276210.205210.471450.428340.541381.10850.72483

Total gas

Sample 88T55/21/DD9; ash-flow tuff; 89.8 mg biotiteJ-value=0.007447±0.25 percent (la)

500600700

*750*800*850*900*950

* 1,000* 1,050*1,150

1,300

0.158380.233131.64353.64283.77303.07983.58295.77079.87465.88231.97170.04820

;lat41°l'29"N.,0.108440.102170.551341.21111.25611.02391.19301.91313.29731.96440.656480.01555

Total gas

0.981.5302.9313.0913.0743.0583.0463.0353.0333.0343.015

; measured 4()Ar/36Ar=298.9long 114°32'41"W.1.470 262.282 642.981 2013.008 4173.004 4833.008 5423.003 4333'.016 2532.995 1762.994 1013.003 273.10 8.12.984

9.027.647.676.686.794.292.290.890.992.2

0.51.03.37.05.2

12.010.913.728.118.4

13±220±238.28±0.1540.34±0.0840.1 ±0.339.92+0.0939.77+0.0639.62+0.1339.60±0.0739.6±0.239.4±0.2

; plateau date=39.89±0.12 Ma;

5.08.6

32.158.061.758.061.367.573.176.378.610.9

0.80.84.19.19.47.79.0

14.424.814.84.90.1

19.6±0.330.4±0.839.61+0.12

'39.96±0.1139.91±0.1539.96±0.1139.90±0.1140.08±0.1339.79+0.1139.79±0.1139.90+0.1341±639.65+0.13

Page 30: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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 ContinuedSample 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.

500600700750800850

*900*950

* 1,000* 1,050*1,150

1,300

0.058260.072910.388150.640681.26012.41423.63914.67526.08897.37739.71670.50310

Total gas

0.034470.024160.122540.200740.396910.761451.15721.49031 .94072.35643.09520.15804

1.693.023.1683.1923.1753.1693.1453.1373.1383.1313.1393.1833.138

204066

118162227277272163885028

12.936.640.679.084.691.093.092.989.985.387.754.4

0.30.21.01.73.46.59.9

12.716.520.126.4

1.3

22±240±241.5±0.641.8±0.341.57±0.1541.50±0.1341.18±0.1241.08±0.1141.09±0.1141.00±0.1141.11±0.1141.7±0.441.09±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.

500600700750800850900950

* 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

0.171630.292292.13221.84271.32900.867560.610220.264511.47741.82421.41640.10708

1.7722.6673.1013.1123.1043.0943.0683.0243.0863.0903.1033.1273.067

301372

230210161988565259.99.2

27.863.585.994.094.191.987.083.585.490.793.276.6

1.42.4

17.314.910.87.04.92.1

12.014.811.50.9

22.76±0.0734.1 ±0.239.63±0.1139.78±0.1139.68±0.1139.55±0.1539.21±0.1538.7±0.339.44±0.1439.49±0.1139.66±0.1140.0±0.739.21±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.

500600700750800850900950

1,0001,0501,1501,300

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

0.238170.317370.573540.559090.657130.710800.839671.22712.25311.91904.38980.48327

1.5891.9232.6182.9813.1103.1353.0993.0763.0593.0893.1073.1493.020

211627487291

1061111141167847

17.838.352.072.683.788.388.587.383.888.792.386.4

1.72.24.03.94.65.05.98.7

15.913.531.0

3.4

20.7±0.225.0±0.334.00±0.1338.67±0.1440.32±0.1340.65±0.1240.18±0.1239.89±0.1139.66±0.1140.05±0.1140.29±0.1140.8±0.239.17±0.12

Page 31: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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.

500600

*700*750*800*850*900*950

* 1,000* 1,050*1,150* 1,300

0.462000.657005.06286.37614.13592.82512.24112.61145.99917.07904.95050.42176

Total gas

0.298330.262231.60032.01511.31080.89960.722690.838101.91462.25191.57100.13207

1.5492.5053.1643.1643.1553.1403.1013.1163.1333.1443.1513.1943.099

273145626761464556503527

23.647.175.589.490.988.982.779.182.686.188.575.4

2.21.9

11.614.69.56.55.26.1

13.916.311.4

1.0

19.73±0.1531.8±0.240.07±0.1140.08±0.1139.97±0.1139.8±0.239.29±0.1539.47±0.1139.69±0.1139.82±0.1139.92±0.1140.4±0.439.27±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 ±0.14700 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±3Total gas 2.685 35.1 ±0.3

Page 32: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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.

800900950

1,0001,025

* 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

0.01070.00580.00850.01390.03290.072750.100680.124290.209260.148000.152020.021210.02110

2.261.411.053.092.712.7772.7622.7852.8232.8262.8772.963.0112.793

0.390.510.300.150.120.120.120.120.120.120.120.120.12

5.425.331.070.673.182.286.990.192.892.094.588.378.3

1.20.60.91.53.67.9

10.913.522.716.116.52.32.3

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 0.5900 0.0167 0.0052 3.22 0.58 15.9 0.3950 0.0038 0.0015 2.4 0.28 14.3 0.1

1,000 0.0062 0.0016 3.7 0.19 25.1 0.11,050 0.0150 0.0046 3.25 0.15 41.7 0.31,100 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 1.0Total gas 2.957

31±320±215±843±437±238.4±0.438.2±0.438.5±0.539.0±0.339.1 ±0.339.8±0.441±241.6±0.838.6±0.8

25±543±733±2450±3543±1041.0±0.639.2±0.439.67±0.1439.34±0.1139.5±0.239.6±0.339.4±0.637±439.5±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.

600800900

1,0001,0501,100

*1,150*1,350

0.03695 0.18778 1.1766 1.2428 0.82265 1.2821 2.2633 3.3878

Total gas

0.019580.148970.423450.425790.287260.447950.771111.1517

1.891.2602.7782.9192.8642.8622.9352.9422.829

1319988757566331

18.520.771.584.380.081.991.995.2

0.5 4.1

11.511.67.8

12.221.031.3

26±317.69±0.1538.8±0.240.70±0.1039.94±0.1339.9±0.340.93±0.1141.02±0.0939.47±0.16

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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.

600700750800850900950

1,0001,0501,1001,150

* 1,200* 1,350

0.050610.156040.197240.243670.456040.635871.12000.984961.21991.94833.07004.01524.7112

Total gas

0.025220.062640.070460.079270.154900.215780.392170.346390.433160.692601.09431.43371.6885

2.012.4912.7993.0742.9442.9472.8562.8432.8162.8132.8052.8012.7902.812

15181920222428344052718325

11.230.441.141.369.885.689.791.792.092.390.690.489.4

0.40.91.11.22.33.25.95.26.5

10.416.421.425.2

28.6±1.135.4±0.339.8±0.543.6±0.441.8±0.241.86±0.1040.59±0.0740.41 ±0.1 440.03±0.0739.98±0.1339.88±0.0639.81 ±0.0739.66±0.0639.97±0.09

FERGUSON MOUNTAINSample 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.

700800900950

1,0001,0501,075

*1,100*1,150* 1,250

1,350

0.195050.175300.029040.021550.142911.10861.70451.29103.17881.22430.06718

Total gas

0.067340.063370.014110.011110.053220.388120.590500.441621.09220.420340.02097

2.902.772.061.942.692.862.8872.9232.9112.9133.202.889

2.51.40.410.340.190.160.160.160.160.160.18

33.420.910.911.144.070.379.387.080.980.480.8

2.12.00.40.41.7

12.318.714.034.513.30.7

39.6±0.337.8±0.728±527±637±139±139.43±0.0739.93±0.0639.76±0.0639.8±0.244±239.5±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.

600700800900

* 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

0.005510.007710.029930.180191.17381.04030.689750.424050.44597

1.933.413.8123.6413.5483-.S333.5413.5493.5453.546

1.53.8

1334

23334340

115192

2.534.827.990.997.398.095.986.778.7

0.10.20.74.5

29.426.017.310.611.2

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

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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 0.046969009259501000102510751,1001,1251,1501,1751,2001,2251,2501,350

0.104320.028960.025470.009650.010970.025060.061740.267940.434860.965830.736360.322910.234180.37716

Total gas

0.039090.010290.007690.004270.004090.009360.019770.087240.138810.305920.234030.102600.074460.12065

N.,long 1] 2.522.672.813.312.262.682.683.123.0713.1333.1573.1463.1473.1453.1263.090

0.590.230.200.170.150.150.140.130.120.120.120.120.110.110.11

24.323.748.257.432.634.845.865.578.186.292.693.692.792.392.0

3.93.20.90.60.40.30.81.67.2

11.525.419.48.56.2

10.0

34±336±238±545±531±1436±1036±542±341.6±0.442.42±0.1442.75±0.1142.60±0.1342.6±0.842.59±0.1642.3±0.541.8±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.

650750850

*950

* 1,0001,0501,1001,1501,350

0.201730.252690.764321.60352.39023.52783.26352.61820.73826

Total gas

0.096520.090540.244050.523480.780411.13211.03190.815070.22428

2.0902.7913.1323.0633.0633.1163.1633.2123.2923.110

3251

1031742812551558216

32.742.284.689.392.090.890.191.891.4

2.01.84.9

10.615.822.920.916.54.5

29.2±0.538.9±0.243.56±0.2042.61 ±0.1042.61 ±0.0743.34±0.0743.98±0.1144.66±0.0945.8±0.343.26±0.11

SANFORD SPRINGSSample 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.

600750800850900950

* 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

0.490081.00770.329240.231910.223570.276600.472890.940231.16040.554180.22861

2.6332.7892.7832.7832.7882.7672.7992.7962.7902.7932.7882.777

435482705968

156254314119

17

72.476.485.084.282.384.492.295.596.195.391.5

8.317.05.63.93.94.78.0

15.919.69.43.9

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

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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 F 39Ar/37Ar 40ArR (percent) 39AfK (percent)

Apparent ageand error (Ma)

GOLD HILLSample 91CP33/21/DD36; rhyolite;J-value=0.005305±0.1 percent (la);

650 0.0415750 0.2422850 0.93339950 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.0.02160.05970.221810.305110.307080.476350.424870.425150.12623

measured 40Ar/36Ar=298.0; plateau date=39.58±0.10 Ma;, long 114°58'15" W.

1.924.0594.2084.2114.1924.1844.1854.1654.1914.161

3.719

123149168140667824

13.549.286.089.390.092.992.593.983.1

0.92.59.4

12.913.020.117.918.05.3

18±238.4±0.339.83±0.0639.86±0.0739.7±0.239.60±0.1139.62±0.0639.42±0.0739.67±0.0639.42±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 0.1485800 0.03057900 0.0189

1,000 0.043641,025 0.049911,050 0.205021,075 0.2893

*1,100 1.1110*1,125 1.8807* 1,1 50 0.02452* 1,200 0.61772

1,350 0.11054Total gas

lat40°ll'23"N.0.026150.009070.004350.010740.012570.050460.07060.264610.451340.05860.147960.02693

, longll4°58'15"W.5.683.374.354.063.974.0634.0994.1994.1674.1804.1754.104.192

0.620.310.310.230.180.160.160.150.150.150.150.13

27.234.848.553.070.482.887.093.795.891.595.483.2

2.30.80.40.91.14.56.2

23.339.8

5.213.12.4

54±232±141 ±439±338±338.6±0.538.9±0.539.8±0.239.54±0.0839.7±0.439.6±0.239±239.8±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 0.0287800 0.0227900 0.0321950 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.,0.00850.005790.010200.017110.097730.321261.02640.929290.221100.14267

long 1153.373.913.152.922.9722.9702.9672.9762.9722.9592.974

measured 40Ar/36Ar=298.9; plateau°37'46" W.

0.640.550.200.160.160.160.160.160.150.14

2.5143952648091948779

date=40.4±0.2 Ma;

0.30.20.40.63.5

11.636.933.4

8.05.1

46±1053±1443±740±440.5±1.140.4±0.240.39±0.1040.51 ±0.1140.4±0.340.3±0.440.5±0.3

Page 36: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

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

DD9DD12DD26DD28DD31DD33DD36DD37DD42DD49

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-36.99x10"*6.48x10"*7.68x10"*6.36x10"*6.81X10"4..

6.94x10^6.30X10"45.95x10"*

±0.03x10"*

( 38Ar/37Ar)Ca

6.91xlQ-52.75x1 0"53.7x1 0"53.02x1 Q-53.17xlO"52.64x1 0-5_

3.67xlO-52-llxlO-52.4x1 0'5

±0.2xlO~5

(4t'Ar/39Ar) K

1.26xlQ-29.07xlO~31.01 IxlO"28.78xlO"39.18xlO"39.76x1 0"3

__

8.99xlQ-37.5xlQ-37.8xlO"3

±0.4x1 0"3

(37Ar/39Ar) K

4.48x1 0"41.82x10"*2.35x10^8.30x1 Q-58.20xlO"5l.lOxlO"4

._

1.49x10"*9.9x1 Q-51.1x10"*

±0.6x10^

(38Ar/39Ar) K

1.30xlO~21.30xl(T21.31xlQ-21.306xl(T21.306xl(T21.307xlO~2 1.313xlO~21.318xlO"21. 306x1 0"2

±0.01 xlO'2

Page 37: Summary of Chemical Analyses and Central Part of the … · Summary of chemical analyses and 40Ar/ 39Ar age-spectra data for Eocene volcanic rocks from the central part of the Northeast

NORTHEAST NEVADA VOLCANIC FIELD K31

t; 7o 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 oP §

H 8 g

o -2 'a,

DH C ^

H

_ OH

SB

- OHsis

CJ

,° O

REFERENCES CITED

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K32 EVOLUTION OF SEDIMENTARY BASINS EASTERN GREAT BASIN

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stratigraphic studies in the Eastern Great Basin: Geological Society of America Memoir 157, p. 183-190.

Mueller, K.J., 1992, Tertiary basin development and exhumation of the northern East Humboldt-Wood Hills metamorphic com­ plex, Elko County, Nevada: Laramie, University of Wyoming, Ph.D. dissertation, 250 p.

Nutt, C.J., and Brooks, W.E., 1994, Geologic map of parts of the Tippett Canyon and Spring Creek Flat NW, Nevada, and Georgetta Ranch, Nevada-Utah, quadrangles, emphasizing Tertiary rocks and including chemical analyses: U.S. Geologi­ cal Survey Open-File Report 94-632, scale 1:50,000.

Potter, C.J., Dubiel, R.F., Snee, L.W., and Good, S.C., 1995, Eocene extension of early Eocene lacustrine strata in a complexly deformed Sevier-Laramide hinterland, northwest Utah and northeast Nevada: Geology, v. 23, p. 181-184.

Sawyer, D.A., and Sargent, K.A., 1989, Petrologic evolution of divergent peralkaline magmas from the Silent Canyon caldera complex, southwestern Nevada volcanic field: Journal of Geo­ physical Research, v. 94, p. 6021-6040.

Sawyer, D.A., Sweetkind, D., Rye, R.O., Siems, D.F., Reynolds, R.L., Rosenbaum, J.G., Lipman, P.W., Boylan, J.A., Barton, P.B., Bethke, P.M., and Curtin, G.C., 1989, Potassium metaso­ matism in the Creede mining district, San Juan Volcanic Field, Colorado, in Continental magmatism abstracts, General Assembly, Santa Fe, New Mexico, June 25-July 1, 1989: New Mexico Bureau of Mines and Mineral Resources Bulletin 131, p. 234.

Scott, R.B., 1965, The Tertiary geology and ignimbrite petrology of the Grant Range, east central Nevada: Houston, Texas, Rice University, Ph.D. dissertation, 116 p.

Shawe, D.R., and Lepry, L.B., 1985, Analytical data for rock samples from the Round Mountain and Manhattan quadran­ gles, Nye County, Nevada: U.S. Geological Survey Open-File Report 85-538, 38 p.

Sidder, G.B., 1994, PETRO.CALC.PLOT, Microsoft Excel macros to aid petrologic interpretation: Computers & Geosciences, v. 20, no. 6, p. 1041-1061.

Steele, Grant, 1960, Pennsylvanian-Permian stratigraphy of east-central Nevada and adjacent Utah: Intermountain Associ­ ation of Petroleum Geologists Annual Field Conference, 11th, Guidebook, p. 93-106.

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Thorman, C.H., Brooks, W.E., Snee, L.W., Potter, C.J., Dubiel, R.J., and Ketner, K.B., 1993, Late Middle Eocene Nanny Creek calc-alkaline volcanic field, NE Nevada and NW Utah; age, extent and implications for Eocene tectonics: Geological Soci­ ety of America Abstracts with Programs, v. 25, no. 5, p. 155.

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NORTHEAST NEVADA VOLCANIC FIELD K33

Geological Survey Miscellaneous Investigations Map 1-2394, Zamudio, J.A., 1992, A synthesis of geologic mapping and remotescale 1:50,000. sensing data analysis for the Dolly Varden Mountains and

Wingate, F.W., 1983, Palynology and age of the Elko Formation Currie Hills, Elko County, Nevada: Boulder, University of(Eocene) near Elko, Nevada: Palynology, v. 7, p. 93-132. Colorado, Ph.D. dissertation, 181 p.

Published in the Central Region, Denver, Colorado Manuscript approved for publication June 21, 1995 Edited by Judith StoeserGraphics 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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SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports of wide and lasting interest and importance to professional scientists and engineers. Included are reports on the results of resource studies and of topographic, hydrologic, and geologic investigations. They also include collections of related papers addressing different aspects of a single sci­ entific topic.

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or geo­ graphic coverage than Professional Papers. They include the results of re­ source studies and of geologic and topographic investigations; as well as collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present sig­ nificant interpretive results of hydrologic investigations of wide interest to professional geologists, hydrologists, and engineers. The series covers investigations in all phases of hydrology, including hydrology, availabil­ ity of water, quality of water, and use of water.

Circulars present administrative information or important scientif­ ic information of wide popular interest in a format designed for distribu­ tion at no cost to the public. Information is usually of short-term interest.

Water-Resources Investigations Reports are papers of an inter­ pretive nature made available to the public outside the formal USGS pub­ lications series. Copies are reproduced on request unlike formal USGS publications, and they are also available for public inspection at deposi­ tories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, maps, and other material that are made available for public consultation at de­ positories. They are a nonpermanent form of publication that may be cit­ ed in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on to­ pographic bases in 7 1/2- or 15-minute quadrangle formats (scales main­ ly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include structure and columnar sections only.

Geophysical Investigations Maps are on topographic or planimet- ric bases at various scales, they show results of surveys using geophysical techniques, such as gravity, magnetic, seismic, or radioactivity, which re­ flect subsurface structures that are of economic or geologic significance. Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or topographic bases of regular and irregular areas at various scales; they present a wide variety of format and subject matter. The series also in­ cludes 7 1/2-minute quadrangle photogeologic maps on planimetric bases which show geology as interpreted from aerial photographs. The series also includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource areas.

Oil and Gas Investigations Charts show stratigraphic informa­ tion for certain oil and gas fields and other areas having petroleum poten­ tial.

Miscellaneous Field Studies Maps are multicolor or black-and- white maps on topographic or planimetric bases on quadrangle or irreg­ ular areas at various scales. Pre-1971 maps show bedrock geology in re­ lation to specific mining or mineral-deposit problems; post-1971 maps are primarily black-and-white maps on various subjects such as environ­ mental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolored or black-and- white maps on topographic or planimetric bases presenting a wide range of geohydrologic data of both regular and irregular areas; the principal scale is 1:24,000, and regional studies are at 1:250,000 scale or smaller.

CatalogsPermanent catalogs, as well as some others, giving comprehensive

listings of U.S. Geological Survey publications are available under the conditions indicated below from USGS Map Distribution, Box 25286, Building 810, Denver Federal Center, Denver, CO 80225. (See latest Price and Availability List.)

"Publications of the Geological Survey, 1879-1961" may be pur­ chased by mail and over the counter in paperback book form and as a set microfiche.

"Publications of the Geological Survey, 1962-1970" may be pur­ chased by mail and over the counter in paperback book form and as a set of microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" may be purchased by mail and over the counter in paperback book form (two vol­ umes, publications listing and index) and as a set of microfiche.

Supplements for 1982, 1983, 1984, 1985, 1986, and for subse­ quent years since the last permanent catalog may be purchased by mail and over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and Wa­ ter-Supply Reports and Maps For (State)," may be purchased by mail and over the counter in paperback booklet form only.

"Price and Availability List of U.S. Geological Survey Publica­ tions," issued annually, is available free of charge in paperback booklet form only.

Selected copies of a monthly catalog "New Publications of the U.S. Geological Survey" is available free of charge by mail or may be ob­ tained over the counter in paperback booklet form only. Those wishing a free subscription to the monthly catalog "New Publications of the U.S. Geological Survey" should write to the U.S. Geological Survey, 582 Na­ tional Center, Reston, VA 22092.

Note.-Prices of Government publications listed in older catalogs, announcements, and publications may be incorrect. Therefore, the prices charged may differ from the prices in catalogs, announcements, and pub­ lications.

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