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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
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 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
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
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
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.
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).
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)
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.
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
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
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.
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
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
§
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
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
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
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
.
T
~11
001
J 1
V\
OT
5/C
T">
D 3
2362
241°1
0'0
2"N
.11
4°57
'02"
W.
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.
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
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
lcan
ic f
ield
Con
tinu
ed.
Loc
ality
Fiel
d N
o.
I
nK
V
[n\-i
a\j r
Nu.
Lat
itude
-
Lon
gitu
de ~
Nor
ther
n E
ast H
urab
oldt
Ran
geQO
FH1
A7\J
LjJ
1/A
D-3
5705
741
°02'
50"
N.
115°
04'1
0"W
.
90B
31B
*D
35
7058
41°0
2'50
"N.
115°
04'1
0"W
.
91T1
1D
-503
360
40°4
2'09
" N
.11
5°04
'20"
W.
91T
12*
D-5
0336
140
°42'
11"N
.11
5°04
'22"
W.
Sout
hern
Eas
t Hur
abol
dt R
ange
91T
13D
-503
362
40°4
1'10
"N.
115°
03'4
7"W
.
91T1
4D
50
3363
40°4
0'10
"N.
115°
02'4
0"W
.
91T
15D
-503
364
40°3
9'34
" N
.11
5°06
'09"
W.
91T
17*
D-5
0336
5 4
0°40
'04"
N.
115°
06'2
2"W
.
Maj
or-o
xide
com
posi
tion
SiO
2A1
203
FeT
O3
MgO
CaO
Na2
OK
2OT
iO,
P20
5M
nOLO
IT
otal
62.0
16.5 5.52
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
99.3
9
61.7
16.0 4.92
1.77
3.74
3.46
2.94
0.61
0.17
0.06
3.45
98.8
2
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
99.3
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 §
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
.
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
-503
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°
05'2
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
o40°4
0'0
4"
NT-
\_7
TA_7
\_r
-T
1>I
.
115°
05'1
1" W
.M
ajor
-oxi
de c
ompo
sitio
n
SiO
2A1
203
FcTO
3M
gOC
aON
a2O
K26
TiO
2P2
O5
MnO
LOI
Tot
al
71.4
12.4 2.00
0.88
2.85
2.25
4.10
0.39
0.14
0.05
2.25
98.7
1
67.5
13.8 1.44
0.72
3.06
2.20
3.00
0.13
0.08
0.02
6.81
98.7
6
53.2
17.0 5.32
3.34
13.3 3.73
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
2.54
5.07
0.68
0.19
0.04
3.09
99.4
8
72.8
11.1 0.97
0.41 1.65
0.75
7.17
0.11
0.15
0.04
4.06
99.2
1
64.3
15.9 3.75
1.60
4.02
3.24
2.43
0.46
0.18
0.07
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
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
.
Loca
lity
Fiel
d N
o.
I ih
Nn
L-«a
U 1
NO
. -
Lat
itude
-
Lon
gitu
de --
Sout
hern
Eas
t H
umbo
ldt R
ange
92B
57
D 5
2259
940
°38'
27"N
.11
5°10
'00"
W.
Dea
dman
Cre
ek a
rea
HI
D-3
6519
241
°15'
N.
114°
37'3
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'
N.
114°
37'3
0"W
.
we
i*t
D-3
6519
741
°18'
52"N
.11
4°38
'30"
W.
HO
L 2
f D
-365
198
41°1
4'36
"N.
114°
37'5
5"W
.
Maj
or-o
xide
com
posi
tion
SiO
2A1
203
FeTO
3M
gOC
aON
a2O
K2O
TiO
2P2
O5
MnO
LOI
Tot
al
65.2
15.7 3.76
1.58
3.79
3.22
3.61
0.54
0.16
0.06
1.97
99.5
9
62.4
16.8 5.67
1.29
2.11
5.07
2.51
0.65
0.21
0.05
2.50
99.2
6
74.9
12.4 1.11
0.43
0.71
2.32
5.00
0.11
0.06
<0.0
22.
2299
.28
63.9
14.6 4.15
0.78
3.59
3.27
4.47
0.60
0.21
0.10
3.70
99.3
7
78.1
11.1 0.84
0.24
0.55
2.96
3.77
0.09
<0.0
5<0
.02
1.61
99.3
3
62.5
17.9 4.46
1.62
1.39
8.17
0.49
0.59
0.19
0.18
1.85
99.3
4
71.7
13.6 1.94
0.56
2.11
3.32
3.93
0.37
0.14
0.02
0.86
98.5
5
60.6
17.2 5.07
2.30
3.63
4.85
2.80
0.74
0.27
0.05
2.02
99.5
3T
race
ele
men
t com
posi
tion
Rb
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
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
.
Loca
lity
Fiel
d N
o.
Lab
No.
Lat
itude
-
Lon
gitu
de
HO
L-5
1D
-365
199
41°1
4'48
"N.
114°
37'2
7"W
.
90-1
41D
-365
200
41°1
6'28
"N.
1 14°
4Q' W
.
Dea
dman
Cre
ek a
rea
90-2
2fD
-365
201
41°1
7'18
"N.
114°
39'5
9"W
.
Woo
d H
ills
90-6
7|D
365
202
41°1
8'58
"N.
114°
39'5
5"W
.
on
TQ+
y\}
/By
DO
/^C
O A
T 3
o5
ZU
j
41°1
8'44
"N.
114°
38'3
2"W
.
92B
WH
l*tt
D-5
2259
041
°04'
53"N
.11
4°52
'55"
W.
nT
D\\
7"L
JO 4
-4-
yzrJ
Wrl
ZT
T
D-5
2259
141
°04'
53"N
.11
4°52
'55"
W.
Ferg
uson
Mou
ntai
n92
T21
*D
-522
586
40°2
6'15
"N.
114°
08'5
4"W
.
Maj
or-o
xide
com
posi
tion
Si0
2A1
2O3
FeTO
3M
gOC
aON
a2O
K2O
TiO
2P2
05
MnO
LOI
Tot
al
74.8
12.7 1.13
0.38
0.57
2.26
5.78
0.10
0.05
0.02
1.86
99.6
5
70.7
12.1 1.16
0.58
1.40
0.85
6.53
0.12
0.05
0.02
5.71
99.2
2
67.5
13.7 4.10
1.33
3.95
2.80
3.43
0.58
0.22
0.02
1.58
99.2
1
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
99.5
2
63.5
16.8 4.75
0.68
4.37
3.80
2.64
0.62
0.19
0.04
1.71
99.1
64.9
15.4 4.36
1.76
4.21
2.81
3.40
0.57
0.18
0.08
1.99
99.6
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
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
Fiel
d N
o.
T ah
Nn
Dol
ly V
arde
n M
ount
ains
92B
DV
*
40°1
9'20
"N.
114°
31'0
9"W
.
Silv
er I
slan
d M
ount
ains
91T
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
'15"
W.
Sanf
ord
Sprin
gs a
rea,
sou
ther
n D
eeo
Cre
ek M
ount
ains
91T
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.
92B
13D
-516
488
114°
10'4
7"W
.
92B
14D
51
6489
Maj
or-o
xide
com
posi
tion
SiO
2A
120
3Fe
TO3
MgO
CaO
Na2
OK
2OT
iO2
P2O
5M
nOLO
IT
otal
64.1
15.2 4.46
2.04
3.74
2.84
3.03
0.55
0.15
0.06
3.16
99.3
3
59.2
17.6 6.06
2.79
6.04
3.14
2.09
0.62
0.19
0.11
1.30
99.1
4
68.0
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
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
98.9
1
60.0
16.0 5.44
3.61
5.84
2.76
2.47
0.75
0.19
0.09
2.22
99.3
7
66.0
15.9 4.28
1.05
3.13
3.34
4.71
0.50
0.21
0.09
<0.0
199
.22
60.6
16.1 5.41
2.18
5.25
2.97
3.99
0.60
0.28
0.12
1.69
99.1
9T
race
ele
men
t co
mpo
sitio
n
Rb
Sr Y Zr Nb
Ba
109
230 24 182 19
977
67 368 19 132 10
1,04
7
84 275 9
122 15
1,04
5
83 490 30 194 15
1,14
3
94 513 21 190 13
1,19
5
75 463 24 174 5
979
189
331 32 234 18
1,16
3
168
383 21 202 11
1,23
4
m o
r
c
H o
o T1 GO m D § H da > GO z GO 00 H m O m H
dd GO 5
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
.
Loca
lity
Fiel
d N
o. -
Lab
No.
Lat
itude
-
Lon
gitu
de
Sanf
ord
Sori
nas
area
, sou
ther
n D
eeo
Cre
ek M
ount
ains
92B
15D
-5 1
6490
39°5
4'16
"N.
OO
13 1
£.
92B
1OD
51
6484
39°5
7'13
"N.
114°
07'0
7"W
.
92B
19D
-5 1
6485
39°5
7'43
"N.
114°
06'4
2"W
.
92B
21D
-5 1
6491
39°5
8'13
"N.
114°
07'5
6"W
.
92B
24D
-5 1
6486
39°5
9'59
" N
.11
4°07
'53"
W.
92B
26D
-5 1
6487
39°5
9'23
" N
.11
4°04
'50"
W.
92B
27*
D-5
164
9839
°48'
39"
N.
114°
07'5
5"W
.
92B
28D
-5 1
6495
39°4
8'24
" N
.11
4°08
'14"
W.
Maj
or-o
xide
com
posi
tion
SiO
2A1
203
FeT
03M
gOC
aON
a2O
K2O
TiO
2P2
05
MnO
LOI
Tot
al
66.4
14.8 4.28
0.80
2.95
2.93
4.82
0.52
0.19
0.08
1.26
99.0
3
67.0
14.8 3.53
0.94
2.63
3.05
4.91
0.45
0.18
0.06
1.51
99.0
6
64.0
15.1 4.43
2.03
3.64
2.77
3.03
0.55
0.15
0.06
3.55
99.3
1
61.3
14.6 5.33
2.13
5.59
2.85
4.11
0.64
0.29
0.1 1.81
98.7
5
65.4
14.8 3.63
1.26
2.94
2.99
4.73
0.45
0.18
0.07
2.56
99.0
1
69.0
13.8 2.55
0.11
3.07
3.28
5.22
0.20
0.10
0.08
1.48
98.8
9
69.2
13.7 1.79
1.54
2.57
2.51
2.84
0.24
0.12
0.04
4.46
99.0
1
60.9
15.7 5.55
3.78
5.74
3.28
2.54
0.77
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
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
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
.62
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
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).
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
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
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
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
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
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
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
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
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
Crittenden, Jr., M.D., Stuckless, J.S., Kistler, R.W., and Stern, T.W., 1973, Radiometric dating of intrusive rocks in the Cottonwood area, Utah: U.S. Geological Survey Journal of Research, v. 1, no. 2, p. 173-178.
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stratigraphic studies in the Eastern Great Basin: Geological Society of America Memoir 157, p. 183-190.
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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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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.