geochronology of cenozoic rocks in the bodie hills ...geochronology of cenozoic rocks in the bodie...

U.S. Department of the InteriorU.S. Geological Survey

Data Series 916

Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

Cover. Steeply flow-banded lava dome, trachyandesite of Willow Springs, east of Warm Spring in the Bodie Hills, California.


By Robert J. Fleck, Edward A. du Bray, David A. John, Peter G. Vikre, Michael A. Cosca, Lawrence W. Snee, and Stephen E. Box

Data Series 916

U.S. Department of the InteriorU.S. Geological Survey

U.S. Department of the InteriorSALLY JEWELL, Secretary

U.S. Geological SurveySuzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:Fleck, R.J., du Bray, E.A., John, D.A., Vikre, P.G., Cosca, M.A., Snee, L.W., and Box, S.E., 2015, Geochronology of Cenozoic rocks in the Bodie Hills, California and Nevada: U.S. Geological Survey Data Series 916, 26 p., http://dx.doi.org/10.3133/ds916.

ISSN 2327-638X (online)

http://www.usgs.gov

http://www.usgs.gov/pubprod

iii

Appendixes[Available for download at http://pubs.usgs.gov/ds/916/]

1. Analytical results of CO2-laser-fusion and resistance-furnace incremental heating 40Ar/39Ar experiments (Menlo Park lab) for samples of the Bodie Hills volcanic field

2. Analytical results of furnace incremental heating 40Ar/39Ar experiments (Denver lab, Snee) for samples of the Bodie Hills volcanic field

3. Analytical results of CO2-laser incremental heating 40Ar/39Ar experiments (Denver lab, Cosca) for samples of the Bodie Hills volcanic field

Contents

Introduction.....................................................................................................................................................140Ar/39Ar Analytical Methods ........................................................................................................................8K-Ar Analytical Methods ..............................................................................................................................9Data.................................................................................................................................................................. 9Acknowledgments .........................................................................................................................................9References Cited..........................................................................................................................................25

Figures 1. Map showing location of and major physiographic features near the Bodie Hills

volcanic field ..........................................................................................................................7 2. Locations of samples with 40Ar/39Ar age determinations shown on a simplified

geologic map of the Bodie Hills volcanic field, California and Nevada .....................10 3. Locations of samples with K-Ar age determinations shown on a simplified geologic

map of the Bodie Hills volcanic field, California and Nevada ......................................12

Tables 1. Map location numbers for 40Ar/39Ar geochronology samples from the Bodie Hills

volcanic field, California and Nevada ................................................................................2 2. Map location numbers for K-Ar geochronology samples from the Bodie Hills volcanic

field, California and Nevada ................................................................................................5 3. Summary compilation of geochronologic data for samples of the Bodie Hills volcanic

field, California and Nevada ..............................................................................................14

Introduction

The purpose of this report is to present geochronologic data for unaltered volcanic rocks, hydrothermally altered volcanic rocks, and mineral deposits of the Miocene Bodie Hills and Pliocene to Pleistocene Aurora volcanic fields of east-central California and west-central Nevada. Most of the data presented here were derived from samples collected between 2000–13, but some of the geochronologic data, compiled from a variety of sources, pertain to samples collected during prior investigations. New data presented here (tables 1 and 2; Appendixes 1–3) were acquired in three U.S. Geological Survey (USGS) 40Ar/39Ar labs by three different geochronologists: Robert J. Fleck (Menlo Park, CA), Lawrence W. Snee (Denver, CO), and Michael A. Cosca (Denver, CO). Analytical methods and data derived from each of these labs are presented separately.

The middle to late Miocene Bodie Hills volcanic field (BHVF) is a large (>700 km2), long-lived (~9 million years [m.y.]), episodic eruptive complex (John and others, 2012) in the southern segment of the ancestral Cascades arc (du Bray and others, written commun., 2015) north of Mono Lake and east of Bridgeport, California (fig. 1). The field is near the west edge of the Walker Lane and the northwest edge of the Mina deflection where structures related to these shear zones may have localized magmatism. The Walker Lane (fig. 1) is a broad, northwest-striking zone of right-lateral shear that accommodates right-lateral motion between the Pacific and North America plates; the Mina deflection constitutes a 60-km-long right step in the Walker Lane (Faulds and Henry, 2008; Oldow, 1992, 2003; Stewart, 1988). The Bodie Hills volcanic field includes at least 31 volcanic rock units erupted from 21 significant volcanic eruptive centers.

Four trachyandesite stratovolcanoes developed along the margins of the volcanic field and numerous silicic trachyandesite to rhyolite flow dome complexes erupted more centrally. Volcanism in the Bodie Hills volcanic field peaked at two periods, ~15.0 to 12.6 million years before present (Ma) and ~9.9 to 8.0 Ma, which were dominated by emplacement of large stratovolcanoes and large silicic trachyandesite-dacite lava domes, respectively. A final period of small-volume silicic dome emplacement began in the western part of the volcanic field at ~6 Ma and culminated at ~5.5 Ma (John and others, 2012).

Compositions of Bodie Hills volcanic rocks vary from ~50 to 78 weight percent SiO2, although rocks with <55 weight percent SiO2 are rare. Rock compositions form a high-potassium (K) calc-alkaline series with pronounced negative titanium-phosphorus-niobium-tantalum anomalies and high barium/niobium, barium/tantalum, and lanthanum/niobium typical of subduction-related continental margin arcs (Gill, 1981). Most rocks are porphyritic and commonly contain 15–35 volume percent phenocrysts of plagioclase, pyroxene, and hornblende±biotite. Although the oldest eruptive centers have the most mafic compositions, erupted rock compositions oscillated between mafic and intermediate to felsic compositions through time. Following a brief hiatus in volcanism, post subduction rocks of the ~3.9- to 0.1-Ma, bimodal, high-K Aurora volcanic field were erupted onto the Bodie Hills volcanic field. Volcanism in the Bodie Hills volcanic field persisted until 8 Ma without apparent changes in rock composition or style of eruption despite the transition from subduction of the Farallon plate beneath the west coast of North America to establishment of a transform plate margin at ~10 Ma (John and others, 2012).

The eastern and southeastern parts of the Bodie Hills volcanic field and Miocene sedimentary rocks on the southern edge of Fletcher Valley are unconformably overlain by Pliocene to late Pleistocene (~3.9 to 0.1 Ma) rocks of the Aurora volcanic field (Gilbert and others, 1968; Al-Rawi, 1969; Chesterman and Gray, 1975; Kleinhampl and others, 1975; Lange and others, 1993; Lange and Carmichael, 1996; Kingdon and others 2013). The field covers ~325 km2 and includes many well-preserved volcanic centers. These centers consist of monogenetic lava and cinder cones, valley-filling lava flows, shield volcanoes, and lava domes. Compositions of the Aurora volcanic field rocks are bimodally distributed and consist principally of trachyandesite and trachydacite to high-silica rhyolite.

Numerous hydrothermal systems were operative in the Bodie Hills during the Miocene (Vikre and others, in press). Structurally focused hydrothermal systems formed large epithermal gold-silver vein deposits in the Bodie and Aurora mining districts that are temporally and spatially related to intermediate- to silicic-composition dome complexes (John and others, 2012).


By Robert J. Fleck, Edward A. du Bray, David A. John, Peter G. Vikre, Michael A. Cosca, Lawrence W. Snee, and Stephen E. Box

2 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

Map location number

Sample number Latitude Longitude Unit; alteration zone; or mining districtAppendix number

1 098-12B 38.38762 −119.18139 Trachyandesite of Masonic 12 098-12A 38.35923 −119.19917 Eureka Valley Tuff 13 MAS10-72 38.40189 −119.13718 Trachyandesite of Masonic Gulch 14 RW08-1 38.41123 −119.12414 Alteration: Red Wash-East Walker River alteration zone 15 MAS10-73 38.39643 −119.13470 Trachyandesite of Masonic Gulch 16 098-12D 38.39951 −119.11939 Trachyandesite of Masonic 17 MAS10-55 38.41419 −119.10259 Alteration: Red Wash-East Walker River alteration zone 18 098-12E 38.39143 −119.12397 Trachyandesite of Masonic Gulch 19 MAS10-75 38.39169 −119.11549 Trachyandesite of Masonic Gulch 1

10 07-BA-38 38.36049 −119.14502 Andesite of Lakeview Spring 111 MAS07-1A 38.34992 −119.14832 Alteration: Masonic mining district, Chemung mine 112 MAS12-10 #1 38.33716 −119.16013 Alteration: Masonic mining district, Success mine 113 MAS12-10 #2 38.33716 −119.16013 Alteration: Masonic mining district, Success mine 114 MAS10-76 38.38169 −119.11534 Trachyandesite of Masonic, plug 115 MAS09-1A 38.35847 −119.13824 Alteration: Masonic mining district, Red Rock mine 116 12-BA-20 38.33410 −119.15949 Trachyandesite of Masonic 117 MAS09-1 38.35783 −119.13268 Alteration: Masonic mining district, Red Rock mine 118 098-12F 38.37542 −119.11418 Trachyandesite of Masonic 119 MAS07-3 38.35968 −119.12682 Alteration: Masonic mining district, Sarita mine 120 07-BA-40 38.36544 −119.11607 Alteration: Masonic mining district, Pittsburg-Liberty mine 121 088-22A 38.36731 −119.10727 Alteration: Masonic mining district, Maybelle mine 122 10-BA-15 38.34130 −119.11570 Trachyandesite of Masonic 123 10-BA-13 38.35154 −119.10419 Trachyandesite of Masonic 124 088-22B 38.37937 −119.07802 Trachyandesite of Masonic 125 MAS11-2B 38.36064 −119.08681 Alteration: Masonic mining district, Perini mine 126 MAS11-1 38.36041 −119.08369 Alteration: Masonic mining district, Perini mine 127 11-BA-40 38.41155 −119.01907 Trachydacite of Rough Creek 128 09-BA-7 38.33786 −119.08727 Trachyandesite of Masonic 129 12-BA-9 38.33679 −119.07378 Trachydacite of East Canyon 130 08SB038 38.40828 −118.97383 Trachyandesite of Del Monte 131 10-BA-29 38.36466 −119.01452 Trachydacite of Rough Creek 132 10-BA-9 38.35278 −119.02068 Trachyandesite of Masonic, plug 133 6-289-2/45/DD72 38.3729 −118.9993 Eureka Valley Tuff 234 10-BA-62 38.36327 −119.00635 Tephra in sedimentary rocks of Fletcher Valley 135 10-BA-6 38.33375 −119.02470 Trachydacite of Rough Creek 136 10-BA-5 38.33945 −118.99699 Pyroxene rhyolite 137 11-BA-41 38.35057 −118.98085 Trachyandesite of Del Monte 138 11-BA-32 38.33637 −118.97804 Rhyolite of Bodie Creek 139 08SB032 38.34561 −118.95580 Unwelded tuff, Fletcher Basin 140 5-152-9/50/72 38.3548 −118.9261 Hornblende trachydacite 241 5-152-9/56/72 38.3548 −118.9261 Hornblende trachydacite 242 12-BA-3 38.34974 −118.84729 Trachyandesite of Mud Spring Canyon 343 10-BA-69 38.30537 −119.13652 Trachyandesite of Masonic 144 098-13D 38.27655 −119.16062 Trachyandesite of Clark Canyon 145 09-BA-43 38.26358 −119.16825 Trachyandesite of Clark Canyon 146 203195 38.2823 −119.1479 Basaltic andesite of Locomotive Point 347 09-BA-47 38.28409 −119.13821 Rhyolite of Bodie Hills 148 09-BA-42 38.27001 −119.14887 Rhyolite of Big Alkali 1

Table 1. Map location numbers for 40Ar/39Ar geochronology samples from the Bodie Hills volcanic field, California and Nevada.

Introduction 3

Map location number


49 088-21A 38.27363 −119.13962 Trachyandesite of Aurora Canyon 150 098-13B 38.26802 −119.13218 Rhyolite of Bodie Hills 151 MC-12-20 38.2701 −119.1261 Hornblende trachyandesite plug 352 088-23F 38.31068 −119.11700 Trachyandesite of Masonic 153 088-23D 38.28113 −119.10206 Trachyandesite of Aurora Canyon 154 088-23A 38.27852 −119.10021 Trachyandesite of Aurora Canyon 155 088-23B 38.27831 −119.09908 Trachyandesite of Aurora Canyon 156 08-BA-62 38.32006 −119.04943 Trachyandesite of Masonic 157 088-25A 38.27322 −119.09077 Trachyandesite of Aurora Canyon 158 09-BA-1 38.31968 −119.04411 Trachyandesite of Cow Camp Creek 359 077-8C 38.27145 −119.07783 Trachyandesite of Aurora Canyon 160 077-8B 38.28334 −119.05617 Trachydacite intrusion 161 088-21B 38.26418 −119.07504 Trachydacite of Potato Peak 162 09-BA-35 38.29048 −119.04642 Trachydacite intrusion 163 09-BA-49 38.26389 −119.04748 Eureka Valley Tuff 164 11-BA-60 38.32693 −118.97204 Rhyolite of Bodie Creek 165 08-BA-65 38.31071 −118.97808 Rhyolite of Bald Peak 166 10-BA-67 38.26200 −118.98300 Rhyolite of Bald Peak 167 AU-10/61/DD61 38.26 −118.981 Eureka Valley Tuff 268 108-11A 38.27826 −118.94807 Rhyolite of Bodie Creek 169 077-9B 38.26971 −118.95063 Rhyolite of Bodie Creek 170 077-9D 38.28562 −118.92803 Rhyolite of Del Monte Canyon 171 AU-6/60/DD61 38.285 −118.928 Rhyolite of Del Monte Canyon 272 077-9C 38.27661 −118.93036 Rhyolite of Del Monte Canyon 173 SAW11-9 38.29036 −118.91657 Alteration: Sawtooth Ridge alteration zone 174 077-9E 38.31905 −118.91003 Trachyandesite of Del Monte 175 10-BA-20 38.31679 −118.91129 Rhyolite of Aurora Creek 176 10-BA-21 38.30315 −118.89740 Rhyolite of Aurora Creek 177 108-10C 38.28052 −118.90623 Trachyandesite of West Brawley Peak 178 108-10A 38.27293 −118.91272 Trachyandesite of Aurora 179 FA1 38.2931 −118.8914 Alteration: Aurora mining district, adularia in Prospectus vein 280 10-BA-27 38.27500 −118.90498 Rhyolite of East Brawley Peak 181 AU-2/59/DD61 38.282 −118.896 Aurora mining district, adularia in Del Monte shaft dump 282 AU-1/58/DD61 38.266 −118.9 Alteration: Aurora mining district, adularia in Esmeralda vein dump 283 00-BA-16 38.2708 −118.8908 Trachyandesite of Aurora 284 MC-12-19 38.31952 −118.78154 Trachyandesite of Borealis 385 39509-10 38.21532 −119.22755 Dacite of Hot Springs Canyon 186 39509-3K 38.20793 −119.22751 Alteration: Cinnabar Canyon-US 395 alteration zone 187 088-24B 38.25504 −119.14115 Trachyandesite of Willow Springs 188 088-24A 38.25278 −119.13951 Rhyolite of Big Alkali 189 PP09-10A1 38.25309 −119.13844 Alteration: Aurora Canyon alteration zone 190 098-13A 38.25754 −119.12788 Rhyolite of Big Alkali 191 CC09-9D1 38.19869 −119.17050 Alteration: Cinnabar Canyon-US 395 alteration zone 192 CC09-9D2 38.19869 −119.17050 Alteration: Cinnabar Canyon-US 395 alteration zone 193 088-24C 38.24786 −119.11208 Trachydacite of Potato Peak 194 12-BA-1 38.18995 −119.16513 Trachydacite of Cinnabar Canyon 195 077-7C 38.19677 −119.15829 Rhyolite of Del Monte Canyon 196 08-BA-46 38.24430 −119.10385 Alteration: Potato Peak alteration zone, Alta Pina mine 1

Table 1.—Continued


Map location number


97 08-BA-50 38.24816 −119.09663 Rhyolite of Bodie Hills 198 077-7B 38.19178 −119.15240 Trachyandesite of Willow Springs 199 098-13C 38.25072 −119.09223 Trachydacite of Potato Peak 1

100 098-10C 38.24919 −119.09203 Trachydacite of Potato Peak 1101 088-21D 38.24330 −119.09209 Trachydacite of Potato Peak 1102 098-10B 38.25135 −119.08382 Rhyolite of Bodie Hills 1103 088-21C 38.25134 −119.08382 Rhyolite of Bodie Hills 1104 088-24D 38.22678 −119.10376 Trachydacite of Potato Peak 1105 088-21E 38.23457 −119.08582 Trachydacite of Potato Peak 1106 088-24E 38.21809 −119.10188 Trachydacite of Potato Peak 1107 08-BA-61 38.20769 −119.10175 Trachydacite of Potato Peak 1108 088-24F 38.20176 −119.08978 Trachyandesite of Willow Springs 1109 108-12A 38.24252 −119.04825 Trachydacite of Potato Peak 1110 08-BA-68 38.19323 −119.06835 Trachydacite of Potato Peak 1111 108-12B 38.23830 −119.00784 Trachydacite of Potato Peak 1112 08-BA-66 38.18629 −119.05680 Dacite of Silver Hill, debris flow clast 1113 12-BA-17 38.21961 −119.00019 Alteration: Bodie mining district, vein adularia, west of Bodie Bluff 1114 077-7F 38.20252 −119.02630 Dacite of Silver Hill 1115 BOD11-3A 38.21961 −119.00354 Alteration: Bodie mining district, vein adularia, Upper Hobart Tunnel dump 1116 BOD11-3B 38.21961 −119.00354 Alteration: Bodie mining district, vein adularia, Bodie Bluff 1117 077-6C 38.21870 −119.00050 Alteration: Bodie mining district, vein adularia, Bodie Bluff 1118 AU-16/63/DD61 38.215 −119.004 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 2119 077-6A 38.21490 −119.00370 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 1120 11-BA-22 38.21257 −119.00402 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 1121 BOD11-4E 38.21257 −119.00402 Alteration: Bodie mining district, vein adularia, Standard Hill Mine 1122 11-BA-21 38.20370 −119.00919 Alteration: Bodie mining district, vein adularia, Red Cloud mine 1123 AU-17/64/DD61 38.215 −118.997 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 2124 BOD09-5 38.20424 −119.00755 Alteration: Bodie mining district, vein adularia, Oro mine dump 1125 11-BA-7G 38.20420 −119.00649 Alteration: Bodie mining district, vein adularia, Silver Hill 1126 BOD09-3 38.20138 −119.00575 Alteration: Bodie mining district, vein adularia, Red Cloud Mine 1127 09-BA-28I 38.20151 −119.00360 Alteration or mineralization: Bodie, Red Cloud mine 1128 AU-18/65/DD61 38.201 −119.004 Alteration or mineralization: Bodie, Red Cloud mine 2129 09-BA-26 38.20360 −119.00021 Dacite of Silver Hill 1130 077-7G 38.23439 −118.96671 Trachyandesite of West Brawley Peak 1131 077-6F 38.18809 −119.00854 Dacite of Silver Hill-Sugarloaf plug 1132 077-9A 38.22088 −118.97443 Eureka Valley Tuff 1133 108-12C 38.18925 −118.98343 Dacite of Silver Hill 1134 108-12E 38.20763 −118.96489 Dacite of Silver Hill 1135 FA66 38.2375 −118.9008 Alteration: East Brawley Peak alteration zone, vein alunite 2136 00-BA-26 38.2542 −118.8841 Trachyandesite of Aurora 2137 AUR10-3 38.23752 −118.89919 Alteration: East Brawley Peak alteration zone, vein alunite 1138 077-7A 38.17860 −119.19476 Trachyandesite of Willow Springs 1139 08-BA-51 38.17449 −119.15441 Trachyandesite of Willow Springs 1140 09-BA-22 38.14302 −119.17974 Trachyandesite of Mt. Biedeman 1141 09-BA-23 38.12851 −119.17491 Tuff of Jacks Spring 1142 098-11B 38.12451 −119.17126 Trachydacite of Bridgeport Canyon 1143 098-11A 38.12239 −119.16954 Tuff of Jacks Spring 1


Introduction 5

Map location number


144 10-BA-46 38.17380 −119.11508 Trachyandesite of Mount Biedeman 1145 10-BA-66 38.17250 −119.10125 Trachydacite of Potato Peak 1146 09SB015A 38.12310 −119.14843 Trachyandesite of Mount Biedeman 1147 098-11E 38.11099 −119.15841 Trachyandesite of Mount Biedeman 1148 077-7D 38.16719 −119.09983 Rhyolite of Bodie Hills 1149 09SB020A 38.13230 −119.13277 Trachydacite of Bridgeport Canyon 1150 108-9A 38.16540 −119.09816 Trachyandesite of Mount Biedeman 1151 108-12F 38.16336 −119.09918 Trachyandesite of Mount Biedeman 1152 MC-12-18 38.15575 −119.07825 Trachyandesite of Mount Biedeman 3153 12-BA-22 38.10151 −119.12400 Trachyandesite of Mount Biedeman 1154 6-181-12/52/DD72 38.1193 −119.1039 Tuff of Jacks Spring 2155 6-181-12/53/DD72 38.1193 −119.1039 Tuff of Jacks Spring 2156 6-215-1/121/72 38.1344 −119.0825 Trachyandesite of Mount Biedeman 2157 119-20B 38.13452 −119.07613 Trachyandesite of Mount Biedeman, plug 1158 09-BA-20 38.15662 −119.04741 Rhyolite of Bodie Hills 1159 10-BA-61 38.14005 −119.01551 Trachyandesite of Mount Biedeman 1160 108-12D 38.17315 −118.97800 Dacite of Silver Hill 1

Map location letter

Sample number Latitude Longitude Unit

A 1071 38.175 −118.832 Pyroxene trachyandesite of Cedar HillB 469 38.179 −118.826 Pyroxene trachyandesite of Cedar HillC 468 38.178 −118.819 Hornblende trachydacite of Cedar HillD 466 38.179 −118.821 Pyroxene trachyandesite of Cedar HillE 465 38.181 −118.823 Pyroxene trachyandesite of Cedar HillF 1069 38.188 −118.850 Hornblende trachydacite of Cedar HillG 139 38.209 −118.880 Hornblende trachydacite of Cedar HillH 199 38.153 −119.008 Hornblende trachydacite of Cedar HillI 144 38.184 −118.894 Trachyandesite of Cedar HillJ 1092A 38.255 −118.810 Rhyolite of Spring PeakK 25 38.261 −118.973 Basaltic trachyandesite of Beauty PeakL 120 38.240 −118.829 Trachyandesite of Mount HicksM 15 38.194 −118.961 Dacite of Silver HillN 414 38.177 −119.193 Trachyandesite of Willow SpringsO 406 38.234 −119.085 Trachydacite of Potato PeakP 507 38.154 −119.089 Rhyolite of Bodie HillsQ 459 38.097 −119.064 Eureka Valley TuffR 31 38.247 −118.990 Eureka Valley TuffS 27 38.247 −118.990 Eureka Valley TuffT W24 38.102 −119.066 Eureka Valley TuffU W25 38.131 −119.181 Eureka Valley TuffV 547 38.255 −118.948 Trachyandesite of West Brawley PeakW USGS(M)-711-67 38.2894 −118.9092 Trachyandesite of Aurora

Table 2. Map location numbers for K-Ar geochronology samples from the Bodie Hills volcanic field, California and Nevada.



Map location letter

Sample number Latitude Longitude Unit

X USGS(M)-668-G10 38.2403 −118.8917 Trachyandesite of AuroraY USGS(M)-711-8 38.2681 −118.8917 Trachyandesite of AuroraZ USGS(M)-712-1 38.2522 −118.9175 Trachyandesite of West Brawley PeakAA USGS(M)-710-7 38.2822 −118.9281 Rhyolite of Del Monte CanyonBB USGS(M)-NTS10B 38.3021 −118.8967 Rhyolite of Aurora CreekCC USGS(M)-Baghdad 38.2786 −118.9467 Rhyolite of Bodie CreekDD USGS(M)-670G4 38.2811 −118.8842 Rhyolite of Martinez HillEE USGS(M)-610-1B 38.2778 −118.8586 Rhyodacite of Aurora PeakFF USGS(M)-672-2 38.3128 −118.8825 Trachyandesite of Aurora CraterGG USGS(M)-611-5 38.2578 −118.8558 Trachyandesite south of Aurora PeakHH BH31 38.194 −119.008 Dacite of Silver Hill, plugII 5 38.0978 −119.1475 Trachyandesite of Sinnamon CutJJ 6 38.1256 −119.1697 Basaltic trachyandesite of RancheriaKK 37 38.287 −118.887 Alteration or mineralization: Trachyandesite of AuroraLL CH8Z1 38.288 −118.882 Trachyandesite of AuroraMM USGS(M)-7346-1 38.215 −119.004 Alteration or mineralization: BodieNN USGS(M)-RCD1B 38.201 −119.005 Alteration or mineralization: BodieOO USGS(M)-B270 38.216 −119.004 Alteration or mineralization: BodiePP USGS(M)-BH15 38.201 −119.003 Dacite of Silver HillQQ USGS(M)-S1 38.188 −119.008 Dacite of Silver HillRR USGS(M)-B271 38.215 −119.003 Dacite of Silver HillSS USGS(M)-856-8 38.214 −119.004 Dacite of Silver HillTT USGS(M)-BH17 38.193 −119.012 Dacite of Silver HillUU USGS(M)-7346-3 38.216 −118.981 Hornblende trachydacite of Cedar HillVV USGS(M)-BH32 38.200 −118.995 Dacite of Silver HillWW USGS(M)-856-32 38.209 −118.997 Dacite of Silver HillXX USGS(M)-856-10 38.205 −119.028 Trachydacite of Potato PeakYY USGS(M)-BH26 38.194 −119.003 Dacite of Silver HillZZ USGS(M)-BH16 38.200 −118.999 Dacite of Silver HillAAA USGS(M)-854-1 38.182 −119.003 Dacite of Silver HillBBB USGS(M)-BH29 38.196 −118.958 Dacite of Silver HillCCC USGS(M)-BM2 38.221 −119.057 Trachydacite of Potato PeakDDD USGS(M)-BH9 38.157 −119.116 Trachyandesite of Mount BiedemanEEE USGS(M)-MTB1 38.146 −119.073 Trachyandesite of Mount BiedemanFFF USGS(M)-BH27 38.140 −119.056 Rhyolite of Bodie HillsGGG USGS(M)-BH19A 38.222 −119.172 Trachyandesite of Willow SpringsHHH USGS(M)-BH6 38.1655 −119.1512 Rhyolite of Big AlkaliIII USGS(M)-BH20 38.220 −119.149 Rhyolite of Big AlkaliJJJ 23 38.156 −118.860 Trachybasalt of Cedar HillKKK 158 38.368 −118.812 Trachyandesite of Mud SpringLLL 160 38.357 −118.896 Trachyandesite of Aurora CraterMMM KA2362 38.4408 −118.9725 Hornblende andesiteNNN KA2364 38.4408 −118.9725 Hornblende andesiteOOO KA2368 38.4408 −118.9725 Hornblende andesitePPP KA2379R 38.4133 −118.9417 Aldrich Station Formation, tuffQQQ 742-45 38.0869 −119.1431 Basaltic trachyandesite of RancheriaRRR EL-KA-2 38.3047 −118.7799 Andesite


Introduction 7

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. M

ap s

how

ing

loca

tion

of a

nd m

ajor

phy

siog

raph

ic fe

atur

es n

ear t

he B

odie

Hill

s vo

lcan

ic fi

eld

(BH)

. Min

a de

flect

ion

(ver

tical

red

line

patte

rn) a

nd o

utlin

e of

the

Wal

ker L

ane

(red

shad

ed a

rea)

mod

ified

from

Fau

lds

and

Henr

y (2

008)

, Bus

by (2

013)

, and

Car

lson

and

oth

ers

(201

3). A

lso

see

John

and

oth

ers,

201

5.


40Ar/39Ar Analytical MethodsNew 40Ar/39Ar age determinations provide temporal

constraints on volcanic and hydrothermal activity in the Bodie Hills (figs. 2 and 3). Volcanic rocks were dated using either separates of one or more phenocryst mineral (plagioclase, sanidine, biotite, hornblende) or whole-rock aggregates. Ages of hydrothermal alteration were determined using separates of alunite, K-feldspar, or adularia. Where practical, multiple minerals from individual samples were dated to provide abundant confirmation of the results, but also to evaluate and document argon systematics of the different mineral phases nucleated under various magmatic and hydrothermal conditions.

Samples collected for 40Ar/39Ar analysis were crushed and sieved to sizes appropriate for preparation of high-purity separates. Standard magnetic and heavy-liquid separation techniques were used to make mineral separations. Whole-rock samples were prepared by crushing and isolating ~1 mm3 rock fragments from fresh rock that was free of obvious alteration and xenocrysts. Analyzed samples were washed in deionized water. In many cases, final separates were prepared by hand picking individual crystals.

Samples whose ages were determined at the U.S. Geological Survey 40Ar/39Ar lab in Menlo Park, CA (Appendix 1) were irradiated in the U.S. Geological Survey TRIGA Reactor Facility in Denver, Colorado; irradiation times were between 10 and 16 hours, although biotite, plagioclase, and sanidine from the rhyolite of Bodie Hills (map location number 102) were also analyzed in both 2-hour and 24-hour irradiations. Plagioclase, biotite, hornblende, and alunite ages were obtained using incremental-heating analysis, that is, incremental extraction of argon at progressively higher temperatures until all gas is released. Incremental heating analyses utilized a low-blank, tantalum and molybdenum, resistance-heated furnace. During heating, all argon gas was released in 8–15 temperature-controlled increments or steps; a few hornblende and potassium feldspar experiments required as many as 18 steps. Ages from incremental-heating experiments were determined by evaluating 40Ar/39Ar age spectra and isochron diagrams. Data for many of the individual sample ages constitute 40Ar/39Ar plateaus, defined as the weighted mean age of contiguous gas fractions representing >50% of the 39Ar released for which no difference can be detected between the ages of any two fractions at the 95% level of confidence (Fleck and others, 1977). Where no plateau was defined, either the 40Ar/39Ar isochron age or the integrated age of all increments was defined as the age of the sample.

Most sanidine and biotite ages determined at the U.S. Geological Survey 40Ar/39Ar lab in Menlo Park, CA were obtained by laser-fusion analysis, whereby grains were fused with a CO2 laser in a single heating step (Appendix 1). One or several grains were used in each analysis, depending on grain size. In all cases, a minimum number of grains were used to permit recognition and elimination of most xenocrystic or

detrital contamination through identification of outliers. The reported age for laser-fusion analyses represents the weighted mean of the replicate analyses, with the inverse variance of propagated, within-run (internal) errors of each used as its weighting factor (Taylor, 1982). Sanidine from the Taylor Creek Rhyolite (TCR-2) was used for calculation of neutron flux in all irradiations up to IRR290 (Appendix 1). Subsequent irradiations (higher IRR numbers in Appendix 1) used Bodie Hills sanidine (098-10B), calibrated to TCR-2, as the flux monitor. Regardless of the monitor mineral used, all ages in Appendix 1 are reported relative to an age of 28.02 Ma for the Fish Canyon Tuff sanidine standard (Renne and others, 1998) with uncertainties estimated at the one-sigma level, unless stated. Decay and abundance constants are those recommended by Steiger and Jäger (1977). Ages were calculated assuming a 40Ar/36Ar ratio of trapped argon equal to the atmospheric value of 295.5.

The 40Ar/39Ar ages reported in Appendix 2, determined in the U.S. Geological Survey 40Ar/39Ar lab in Denver, Colorado by L.W. Snee, are based on analyses of biotite, hornblende, plagioclase, or sanidine phenocrysts; hydrothermal K-feldspar, adularia, or alunite; and one whole rock analysis (Appendix 2). Analyzed materials were packaged in aluminum foil and stacked in quartz glass vials with monitor minerals placed between every second sample and at the top and bottom of each vial. Samples were irradiated in the U.S. Geological Survey’s TRIGA reactor in Denver, Colorado, in irradiation packages DD61, DD72, and DD78. Irradiated samples were heated in temperature steps in a double-vacuum furnace, and the released gasses were cleaned according to procedures described by Snee (2002). Argon isotopic total abundances (40ArT,

39ArT, 38ArT,

37ArT, and 36ArT) were measured on a MAP 215 mass spectrometer on a Faraday collector in volts to five decimal places. Corrected abundances for 40ArR (radiogenic 40Ar), 40ArK (irradiation-produced K-derived 40Ar), 40ArI (initial 40Ar), 39ArK (irradiation-produced K-derived 39Ar), 38ArCl (irradiation-produced Cl-derived 38Ar), 37ArCa (irradiation produced Ca-derived 37Ar, and 36ArI (initial 36Ar) are in volts. All estimated uncertainties in measured voltages are reported in Appendix 2 at one sigma. Voltages may be converted to moles using 1.160×10−12 moles argon per volt signal. The “F” value (40ArR/39ArK) for each temperature step was directly calculated from 40ArR divided by 39ArK. K/Ca was calculated from the expression K/Ca=0.5(39ArK/37ArCa). All isotopic abundances in Appendix 2 have been corrected for mass discrimination. Mass discrimination was determined by calculating the 40Ar/36Ar ratio of aliquots of atmospheric argon pipetted from a fixed pipette on the extraction line; the ratio during these experiments was 298.9, which was corrected to 295.5 to account for mass discrimination. Final isotopic abundances were corrected for all interfering isotopes of argon including atmospheric argon. 37Ar and 39Ar, which are produced during irradiation, are radioactive and their

Acknowledgments 9

abundances were corrected for radioactive decay. Abundances of interfering isotopes from K and Ca were calculated from reactor production ratios determined by irradiating and analyzing pure CaF2 and K2SO4; the K2SO4 was degassed in a vacuum furnace prior to irradiation to release extraneous argon. Corrections for Cl-derived 36Ar were determined using the method of Roddick (1983). Production ratios for these experiments are documented by Snee (2002). Apparent ages of each fraction include the error in J value (0.1 percent), which was calculated from the reproducibility of splits of the argon from several standards. The standards for this experiment were hornblende MMhb-1, using an age of 523.1±2.6 Ma (Samson and Alexander, 1987; Renne and others, 1998), and sanidine FCT1, using an age of 27.84 Ma, as measured in the Denver Argon Laboratory against MMhb-1 (Snee, 2002). Apparent ages were calculated using decay constants of Steiger and Jäger (1977). All apparent age errors are cited at one sigma. Uncertainties associated with apparent ages of individual fractions were calculated using equations of Dalrymple and others (1981). Isochron diagrams were produced for all samples and may be derived by using 40ArI (initial 40Ar) and 36ArI (initial 36Ar). Plateaus were determined according to the method of Fleck and others (1977).

The 40Ar/39Ar ages reported in Appendix 3, determined in the U.S. Geological Survey 40Ar/39Ar lab in Denver, CO by M.A. Cosca, are based on analyses of amphibole (hornblende), plagioclase, and whole rock samples. Samples, together with standards, were irradiated for 20 MW (megawatt) hours in the central thimble position of the USGS TRIGA reactor. Laser fusion of >10 individual Fish Canyon Tuff sanidine crystals (28.201±0.09 Ma; Kuiper and others, 2008) at each closely monitored position within the irradiation package resulted in neutron flux ratios reproducible to ±0.25% (two sigma). Isotopic production ratios and interfering nucleogenic reactions were determined from irradiated CaF2 and KCl salts and zero age K-silicate glass, and for this study the following values were measured: (36Ar/37Ar)Ca=(2.77 ± 0.03)×10−4; (39Ar/37Ar)Ca=(6.54 ± 0.33)×10−4; and (38Ar/39Ar)K=(1.29 ± 0.03)×10−2. Cadmium shielding during irradiation prevented any measurable nucleogenic (40Ar/39Ar)K. The irradiated samples and standards were loaded into numbered positions of a stainless steel planchette, placed into a laser sample chamber with an externally pumped ZnSe window, and evacuated to ultrahigh vacuum conditions in a fully automated stainless steel extraction line designed and built at the USGS in Denver. The samples were incrementally heated using a 25W CO2 laser equipped with a beam homogenizing lens and the liberated gas was expanded and purified by exposure to a cryogenic trap maintained at −140 °C and two hot SAES GP50 getters. Following purification the gas was expanded online into a Thermo Scientific ARGUS VI mass spectrometer (except sample 203195, which was analyzed using a Mass Analyzer Products 215–50 mass spectrometer) in static mode and Ar isotopes were measured by peak jumping using an electron multiplier in analog mode. Data were acquired during 10 measurement cycles and time zero intercepts were determined

by best-fit linear and (or) polynomial regressions to the data. Ages were calculated assuming a 40Ar/36Ar ratio of trapped argon equal to the atmospheric value of 298.56 (Lee and others, 2006) and using decay constants of Steiger and Jäger (1977). Data were corrected for mass discrimination, blanks, radioactive decay, and interfering nucleogenic reactions.

K-Ar Analytical MethodsConventional K-Ar analyses were not carried out as part

of the this study, but previous workers produced considerable K-Ar age data that constitute an important source of stratigraphic information on the Bodie Hills volcanic field and on the timing of mineralization in the Bodie and Aurora mining districts. Many earlier K-Ar analyses were performed in K-Ar laboratories at USGS facilities in Menlo Park and Denver or at University of California laboratories in Berkeley. An appropriate reference for K-Ar techniques used in all three laboratories is found in Dalrymple and Lanphere (1969).

DataAll available geochronology data for Bodie Hills volcanic

field are summarized in table 3. These data are synthesized and interpreted in other publications, including John and others (2012, 2015), Vikre and others (2015) and du Bray and others (written commun., 2015). As described previously, ages reported in Appendixes 1–3 utilized several slightly different ages for the Fish Canyon Tuff sanidine standard as a consequence of these age determinations having been conducted in several different labs, over a period of almost fifteen years, during which the accepted age for the sanidine standard was refined. In order to render ages calculated using different values for the sanidine standard comparable, ages calculated using a sanidine standard age different from 28.02 Ma were recalculated using that value and are summarized in the column titled “Age recalculated for FCT= 28.02” (table 3).

AcknowledgmentsGeologic mapping and sample collection for this study

were conducted as part of the Mineral Systems of the Ancestral and Modern Cenozoic Cascades Arcs Project funded by the U.S. Geological Survey Mineral Resources Program. Technical assistance was provided in Menlo Park laboratories by Dean Miller, Donald Shamp, and James Saburomaru. In Denver, Ross Yeoman and John Lee offered similar assistance. Byron R. Berger (deceased) introduced L.W. Snee to the geology of the Bodie Hills and was instrumental in geochronology sample collection. Constructive reviews by R.D. Taylor and J.N. Aleinikoff are much appreciated and helped clarify data presentation.


Figu

re 2

. (A

) Loc

atio

ns o

f sam

ples

(sol

id b

lack

circ

les)

with

40Ar

/39Ar

age

det

erm

inat

ions

(tab

le 1

) sho

wn

on a

sim

plifi

ed g

eolo

gic

map

of t

he B

odie

Hill

s vo

lcan

ic fi

eld,

Ca

lifor

nia

and

Nev

ada.

Col

ored

pol

ygon

s po

rtray

ext

ent o

f eru

ptiv

e pr

oduc

ts a

ssoc

iate

d w

ith p

artic

ular

vol

cani

c ce

nter

s w

ithin

the

Bodi

e Hi

lls v

olca

nic

field

(mod

ified

fro

m J

ohn

and

othe

rs, 2

012;

201

5). U

ncol

ored

are

as a

re u

nder

lain

by

eith

er o

lder

bas

emen

t roc

ks, r

ocks

of t

he A

uror

a vo

lcan

ic fi

eld,

or s

urfic

ial d

epos

its. (

B) In

set m

ap

show

ing

loca

tions

of s

ampl

es (s

olid

circ

les)

with

40Ar

/39Ar

age

det

erm

inat

ions

(tab

le 1

) in

dens

ely

sam

pled

Bod

ie m

inin

g di

stric

t.

CALIFORNIA

NEVADA

Mt.

Bied

eman

Pota

toPe

akBo

die

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ntai

n

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onic

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ntai

n

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ley

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s

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tyPe

ak

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raCr

ater

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k

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o La

ke

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o V

alle

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rt

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r

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ra

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on Big

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onic

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oir

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7

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98

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95

94

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159

158

157

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153

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146

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140

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113

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107

106

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t m

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lite

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s

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ald

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Rhyo

lite

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odie

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ek

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hyan

desi

te o

f Aur

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Cany

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lite

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ock

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ngs

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on

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hyan

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te o

f Del

Mon

te

Trac

hyda

cite

of B

ridg

epor

t Can

yon

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lite

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el M

onte

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Rhyo

lite

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uror

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eek

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hyan

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te o

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t Bra

wle

y Pe

ak

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altic

trac

hyan

desi

te o

f Ran

cher

ia

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hyda

cite

of R

ough

Cre

ek

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hyan

desi

te o

f Aur

ora

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hyan

desi

te o

f Eas

t Can

yon

Trac

hyan

desi

te o

f Mud

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ing

Cany

on

Trac

hyan

desi

te o

f Mas

onic

EXPL

AN

ATIO

N

40A

r/39

Ar s

ampl

e lo

calit

y

!

!!

122 125 129

120,121

119

117

115,116

127

124

126

B

128

123118

Ç

Tailings Pond

Ç

#

#

!

!

!

!

!!

!

!

!

!

!

!

119°00'119°01'

38°13'

38°12'

0 1 KILOMETER

Main road

40Ar/39Ar sample locality

Mine

Bodie Bluff

RED CLOUD MINE

Bodie

Silver Hill

EXPLANATION

Figure 2.—Continued

Figure II 11


Figu

re 3

. (A

) Loc

atio

ns o

f sam

ples

(sol

id b

lack

circ

les)

with

K-A

r age

det

erm

inat

ions

(tab

le 2

) sho

wn

on a

sim

plifi

ed g

eolo

gic

map

of t

he B

odie

Hill

s vo

lcan

ic fi

eld,

Ca

lifor

nia

and

Nev

ada.

Col

ored

pol

ygon

s po

rtray

ext

ent o

f eru

ptiv

e pr

oduc

ts a

ssoc

iate

d w

ith p

artic

ular

vol

cani

c ce

nter

s w

ithin

the

Bodi

e Hi

lls v

olca

nic

field

(mod

ified

from

Jo

hn a

nd o

ther

s, 2

012;

201

5). (

B) In

set m

ap s

how

ing

loca

tions

of s

ampl

es (s

olid

circ

les)

with

K-A

r age

det

erm

inat

ions

(tab

le 2

) in

dens

ely

sam

pled

Bod

ie m

inin

g di

stric

t.

Inse

t m

apM

118°

45'

118°

50'

118°

55'

119°

00'

119°

05'

119°

10'

119°

15'

38°2

5'

38°2

0'

38°1

5'

38°1

0'

38°0

5'

CALIFORNIA

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t. Bi

edem

an

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toPe

akBo

die

Mou

ntai

n

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onic

Mou

ntai

n

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ley

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s

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tyPe

ak

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raCr

ater

Bald

Pea

k

Mon

o La

ke

Bod

ie

Rough

Creek

East

Walker

Rive

r

395

Auro

ra

Cany

on Big

Alka

li

Bodie

Creek

167

182

Mas

onic

The

Elbo

w

395

Aur

ora

WASSUK RANGE

Flet

cher

Valle

y

Brid

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rtRe

serv

oir

SWEETWATERMOUNTAINS

A

Mon

o V

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y

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II QQ

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man

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e B

odie

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s

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lite

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ek

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lite

of R

ock

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ngs

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on

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hyan

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te o

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Mon

te

Trac

hyda

cite

of B

ridg

epor

t Can

yon

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lite

of D

el M

onte

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yon

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lite

of A

uror

a Cr

eek

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hyan

desi

te o

f Wes

t Bra

wle

y Pe

ak

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altic

trac

hyan

desi

te o

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cher

ia

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cite

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ough

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ek

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Spr

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EXPL

AN

ATIO

N

40A

r/39

Ar s

ampl

e lo

calit

y

#

#

Ç

RED CLOUD MINE

Tailings Pond

119°01'

38°13'

38°12'

119°

1 KILOMETER0

B

HH

TT

YY

VVZZ

PPNN

WW

RR

OO

MM

SS

Bodie Bluff

Bodie

Silver Hill

!

Main road

K-Ar sample locality

Mine

EXPLANATION

Ç

Figure 3.—Continued

Figure III 13

14 Geochronology of Cenozoic Rocks in the Bodie Hills, California and NevadaTa

ble

3.

Sum

mar

y co

mpi

latio

n of

geo

chro

nolo

gic

data

for s

ampl

es o

f the

Bod

ie H

ills

volc

anic

fiel

d, C

alifo

rnia

and

Nev

ada.

Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

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e

158

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hyan

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ud S

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ount

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desit

e of C

ow C

amp

Cree

k2.

000.

04A

r-Ar4

14W

hole

rock

——

1.99

1.99

USG

S(M

)-611

-5—

38.2

578

−118

.855

8Tr

achy

ande

site s

outh

of

Aur

ora P

eak

2.2

0.1

K-A

r2

Who

le ro

ckol

d*2.

3—

2.3

USG

S(M

)-611

-5—

38.2

578

−118

.855

8Tr

achy

ande

site s

outh

of

Aur

ora P

eak

2.5

0.2

K-A

r2

Hor

nble

nde

old*

2.6

—2.

6

USG

S(M

)-670

G4

—38

.281

1−1

18.8

842

Rhyo

lite o

f Mar

tinez

Hill

2.5

0.1

K-A

r2

Biot

iteol

d*2.

6—

2.6

23—

38.1

56−1

18.8

60Tr

achy

basa

lt of

Ced

ar H

ill2.

600.

06K

-Ar

8G

roun

dmas

sne

w—

—2.

60U

SGS(

M)-6

10-1

B—

38.2

778

−118

.858

6Tr

achy

daci

te o

f Aur

ora P

eak

2.5

0.2

K-A

r2

Biot

iteol

d*2.

6—

2.6

USG

S(M

)-610

-1B

—38

.277

8−1

18.8

586

Trac

hyda

cite

of A

uror

a Pea

k2.

70.

2K

-Ar

2H

ornb

lend

eol

d*2.

8—

2.8

1071

KA

-199

938

.175

−118

.832

Pyro

xene

trac

hyan

desit

e of

Ceda

r Hill

6 1.0

0.1

K-A

r1

Plag

iocl

ase

old*

6 1.0

—6 1

.0

469

KA

-200

338

.179

−118

.826

Pyro

xene

trac

hyan

desit

e of

Ceda

r Hill

2.7

0.8

K-A

r1

Plag

iocl

ase

old*

2.8

—2.

8

466

KA

-191

238

.179

−118

.821

Pyro

xene

trac

hyan

desit

e of

Ceda

r Hill

2.7

0.2

K-A

r1

Biot

iteol

d*2.

8—

2.8

465

KA

-185

738

.181

−118

.823

Pyro

xene

trac

hyan

desit

e of

Ceda

r Hill

6 6.2

2.5

K-A

r1

Plag

iocl

ase

old*

6 6.4

—6 6

.4

25K

A-2

086

38.2

61−1

18.9

73Ba

salti

c tra

chya

ndes

ite o

f Be

auty

Pea

k2.

80.

1K

-Ar

1W

hole

rock

old*

2.9

—2.

9

468

KA

-185

938

.178

−118

.819

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill2.

80.

4K

-Ar

1Pl

agio

clas

eol

d*2.

9—

2.9

1069

KA

-200

238

.188

−118

.850

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill2.

50.

3K

-Ar

1Pl

agio

clas

eol

d*2.

6—

2.6

1069

KA

-200

438

.188

−118

.850

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill2.

50.

1K

-Ar

1Bi

otite

old*

2.6

—2.

6

[Ent

ries i

n th

e “S

umm

ary

age”

col

umn

repr

esen

t a re

capi

tula

tion

of K

-Ar a

ges,

reca

lcul

ated

usi

ng th

e de

cay

cons

tant

s of S

teig

er a

nd a

nd Jä

ger (

1977

), an

d 40

Ar/39

Ar a

ges,

calc

ulat

ed a

ssum

ing

a Fi

sh C

anyo

n Tu

ff ag

e of

28.

02 M

a]

Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

139

KA

-198

438

.209

−118

.880

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill3.

40.

3K

-Ar

1Bi

otite

old*

3.5

—3.

5

139

KA

-198

4R38

.209

−118

.880

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill3.

10.

3K

-Ar

1Bi

otite

old*

3.2

—3.

2

139

KA

-199

338

.209

−118

.880

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill2.

31.

6K

-Ar

1Pl

agio

clas

eol

d*2.

4—

2.4

199

KA

-198

038

.153

−119

.008

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill3.

20.

7K

-Ar

1Pl

agio

clas

eol

d*3.

3—

3.3

USG

S(M

)-734

6-3

—38

.216

−118

.981

Hor

nble

nde t

rach

ydac

ite o

f Ce

dar H

ill2.

70.

1K

-Ar

6W

hole

rock

old*

2.8

—2.

8

5-15

2-9/

50/7

2—

38.3

548

−118

.926

1H

ornb

lend

e tra

chyd

acite

3.04

0.03

Ar-A

r39

Who

le ro

ck—

—3.

063.

065-

152-

9/56

/72

—38

.354

8−1

18.9

261

Hor

nble

nde t

rach

ydac

ite3.

530.

18A

r-Ar3

9Pl

agio

clas

e—

—3.

553.

5514

4K

A-2

076

38.1

84−1

18.8

94Tr

achy

ande

site o

f Ced

ar H

ill3.

60.

4K

-Ar

1Pl

agio

clas

eol

d*3.

7—

3.7

1092

AK

A-2

066

38.2

55−1

18.8

10Rh

yolit

e of S

prin

g Pe

ak3.

60.

1K

-Ar

1Sa

nidi

neol

d*3.

7—

3.7

2031

95—

38.2

823

−119

.147

9Ba

salti

c and

esite

of

Loco

mot

ive P

oint

3.9

0.06

Ar-A

r414

Gro

undm

ass

——

3.87

3.87

USG

S(M

)-BH

6—

38.1

655

−119

.151

2Rh

yolit

e of B

ig A

lkal

i5.

70.

2K

-Ar

6Bi

otite

old*

5.9

—5.

9U

SGS(

M)-B

H20

—38

.220

−119

.149

Rhyo

lite o

f Big

Alk

ali

5.2

0.3

K-A

r6

Biot

iteol

d*5.

3—

5.3

USG

S(M

)-BH

20—

38.2

20−1

19.1

49Rh

yolit

e of B

ig A

lkal

i5.

40.

6K

-Ar

6H

ornb

lend

eol

d*5.

5—

5.5

077-

7C—

38.1

9677

−119

.158

29Rh

yolit

e of B

ig A

lkal

i5.

478

0.02

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

5.47

808

8-24

A—

38.2

5278

−119

.139

51Rh

yolit

e of B

ig A

lkal

i6.

201

0.02

6A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

6.20

109

8-13

A—

38.2

5754

−119

.127

88Rh

yolit

e of B

ig A

lkal

i6.

173

0.02

8A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

6.17

309

-BA

-42

—38

.270

01−1

19.1

4887

Rhyo

lite o

f Big

Alk

ali

5.45

50.

025

Ar-A

r7

Biot

iteFC

T=28

.02

——

5.45

539

509-

10—

38.2

153

−119

.227

55D

acite

of H

ot S

prin

gs C

anyo

n8.

070

0.01

7A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.07

041

4K

A-1

973

38.1

77−1

19.1

93Tr

achy

ande

site o

f Will

ow

Sprin

gs7.

80.

2K

-Ar

1Pl

agio

clas

eol

d*8.

0—

8.0

USG

S(M

)-BH

19A

—38

.222

−119

.172

Trac

hyan

desit

e of W

illow

Sp

rings

8.0

0.2

K-A

r6

Biot

iteol

d*8.

2—

8.2

077-

7A—

38.1

7860

−119

.194

76Tr

achy

ande

site o

f Will

ow

Sprin

gs8.

004

0.03

7A

r-Ar

7Bi

otite

FCT=

28.0

2—

—8.

004

077-

7A—

38.1

7860

−119

.194

76Tr

achy

ande

site o

f Will

ow

Sprin

gs8.

051

0.01

9A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.05

1

077-

7B—

38.1

9178

−119

.152

40Tr

achy

ande

site o

f Will

ow

Sprin

gs8.

122

0.02

9A

r-Ar

7Bi

otite

FCT=

28.0

2—

—8.

122

077-

7B—

38.1

9178

−119

.152

40Tr

achy

ande

site o

f Will

ow

Sprin

gs8.

070

0.02

1A

r-Ar

7H

ornb

lend

eFC

T=28

.02

——

8.07

0

077-

7B—

38.1

9178

−119

.152

40Tr

achy

ande

site o

f Will

ow

Sprin

gs8.

139

0.02

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.13

9

088-

24B

—38

.255

04−1

19.1

4115

Trac

hyan

desit

e of W

illow

Sp

rings

8.57

50.

022

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

575

Tabl

e 3.

—Co

ntin

ued

Table III 15


Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

088-

24F

—38

.201

76−1

19.0

8978

Trac

hyan

desit

e of W

illow

Sp

rings

8.15

50.

019

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

155

08-B

A-5

1—

38.1

7449

−119

.154

41Tr

achy

ande

site o

f Will

ow

Sprin

gs8.

305

0.01

7A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

8.30

5

12-B

A-1

—38

.189

95−1

19.1

6512

Trac

hyda

cite

of C

inna

bar

Cany

on8.

548

0.02

8A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.54

8

406

KA

-199

038

.234

−119

.085

Trac

hyda

cite

of P

otat

o Pe

ak8.

40.

2K

-Ar

1Pl

agio

clas

eol

d*8.

6—

8.6

USG

S(M

)-856

-10

—38

.205

−119

.028

Trac

hyda

cite

of P

otat

o Pe

ak8.

90.

2K

-Ar

6Bi

otite

old*

9.1

—9.

1U

SGS(

M)-8

56-1

0—

38.2

05−1

19.0

28Tr

achy

daci

te o

f Pot

ato

Peak

9.0

0.2

K-A

r6

Hor

nble

nde

old*

9.2

—9.

2U

SGS(

M)-B

M2

—38

.221

−119

.057

Trac

hyda

cite

of P

otat

o Pe

ak9.

10.

1K

-Ar

6Bi

otite

old*

9.3

—9.

308

8-21

B Ru

n 2

—38

.264

18−1

19.0

7504

Trac

hyda

cite

of P

otat

o Pe

ak8.

927

0.01

0A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.92

708

8-21

D—

38.2

4330

−119

.092

09Tr

achy

daci

te o

f Pot

ato

Peak

8.96

40.

027

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

964

088-

21E

—38

.234

57−1

19.0

8582

Trac

hyda

cite

of P

otat

o Pe

ak8.

863

0.05

0A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.86

308

8-24

C—

38.2

4786

−119

.112

08Tr

achy

daci

te o

f Pot

ato

Peak

8.99

60.

025

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

996

088-

24D

—38

.226

78−1

19.1

0376

Trac

hyda

cite

of P

otat

o Pe

ak9.

056

0.04

5A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.05

608

8-24

E—

38.2

1809

−119

.101

88Tr

achy

daci

te o

f Pot

ato

Peak

8.92

60.

025

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

926

08-B

A-6

8—

38.1

9323

−119

.068

35Tr

achy

daci

te o

f Pot

ato

Peak

8.99

0.02

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

9909

8-10

C—

38.2

4919

−119

.092

03Tr

achy

daci

te o

f Pot

ato

Peak

8.98

20.

023

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

982

098-

13C

—38

.250

72−1

19.0

9223

Trac

hyda

cite

of P

otat

o Pe

ak8.

998

0.02

1A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.99

810

8-12

A—

38.2

4252

−119

.048

25Tr

achy

daci

te o

f Pot

ato

Peak

8.96

30.

016

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

963

108-

12B

—38

.238

30−1

19.0

0784

Trac

hyda

cite

of P

otat

o Pe

ak9.

032

0.02

2A

r-Ar

7Bi

otite

FCT=

28.0

2—

—9.

032

10-B

A-6

6—

38.1

7250

−119

.101

25Tr

achy

daci

te o

f Pot

ato

Peak

8.74

90.

019

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

749

10-B

A-6

6—

38.1

7250

−119

.101

25Tr

achy

daci

te o

f Pot

ato

Peak

8.73

50.

015

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—8.

735

15K

A-1

972

38.1

94−1

18.9

61D

acite

of S

ilver

Hill

8.9

0.2

K-A

r1

Plag

iocl

ase

old*

9.1

—9.

1U

SGS(

M)-B

H15

—38

.201

−119

.003

Dac

ite o

f Silv

er H

ill8.

60.

4K

-Ar

6H

ornb

lend

eol

d*8.

8—

8.8

USG

S(M

)-BH

15—

38.2

01−1

19.0

03D

acite

of S

ilver

Hill

8.7

0.2

K-A

r6

Biot

iteol

d*8.

9—

8.9

USG

S(M

)-S1

—38

.188

−119

.008

Dac

ite o

f Silv

er H

ill8.

50.

4K

-Ar

6W

hole

rock

old*

8.7

—8.

7U

SGS(

M)-S

1—

38.1

88−1

19.0

08D

acite

of S

ilver

Hill

8.3

0.4

K-A

r6

Plag

iocl

ase

old*

8.5

—8.

5U

SGS(

M)-S

1—

38.1

88−1

19.0

08D

acite

of S

ilver

Hill

8.9

0.4

K-A

r6

Plag

iocl

ase

old*

9.1

—9.

1U

SGS(

M)-B

271

—38

.215

−119

.003

Dac

ite o

f Silv

er H

ill8.

40.

2K

-Ar

6H

ornb

lend

eol

d*8.

6—

8.6

USG

S(M

)-B27

1—

38.2

15−1

19.0

03D

acite

of S

ilver

Hill

8.5

0.3

K-A

r6

Plag

iocl

ase

old*

8.7

—8.

7U

SGS(

M)-8

56-8

—38

.214

−119

.004

Dac

ite o

f Silv

er H

ill8.

20.

2K

-Ar

6W

hole

rock

old*

8.4

—8.

4U

SGS(

M)-8

56-8

—38

.214

−119

.004

Dac

ite o

f Silv

er H

ill9.

20.

5K

-Ar

6H

ornb

lend

eol

d*9.

4—

9.4

USG

S(M

)-BH

17—

38.1

93−1

19.0

12D

acite

of S

ilver

Hill

9.2

0.5

K-A

r6

Hor

nble

nde

old*

9.4

—9.

4U

SGS(

M)-B

H32

—38

.200

−118

.995

Dac

ite o

f Silv

er H

ill8.

80.

2K

-Ar

6Bi

otite

old*

9.0

—9.

0U

SGS(

M)-8

56-3

2—

38.2

09−1

18.9

97D

acite

of S

ilver

Hill

8.9

0.3

K-A

r6

Biot

iteol

d*9.

1—

9.1

USG

S(M

)-BH

26—

38.1

94−1

19.0

03D

acite

of S

ilver

Hill

9.1

0.5

K-A

r6

Hor

nble

nde

old*

9.3

—9.

3U

SGS(

M)-B

H16

—38

.200

−118

.999

Dac

ite o

f Silv

er H

ill9.

40.

2K

-Ar

6Bi

otite

old*

9.7

—9.

7U

SGS(

M)-8

54-1

—38

.182

−119

.003

Dac

ite o

f Silv

er H

ill8.

70.

2K

-Ar

6Bi

otite

old*

8.9

—8.

9

Tabl

e 3.

—Co

ntin

ued

Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

USG

S(M

)-BH

29—

38.1

96−1

18.9

58D

acite

of S

ilver

Hill

8.7

0.2

K-A

r6

Biot

iteol

d*8.

9—

8.9

077-

7F—

38.2

0252

−119

.026

30D

acite

of S

ilver

Hill

8.92

80.

024

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

928

09-B

A-2

6—

38.2

0360

−119

.000

21D

acite

of S

ilver

Hill

9.13

20.

020

Ar-A

r7

Biot

iteFC

T=28

.02

——

9.13

210

8-12

C—

38.1

8925

−118

.983

43D

acite

of S

ilver

Hill

9.08

90.

014

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

089

108-

12D

—38

.173

15−1

18.9

7800

Dac

ite o

f Silv

er H

ill9.

018

0.01

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.01

810

8-12

E—

38.2

0763

−118

.964

89D

acite

of S

ilver

Hill

9.14

00.

020

Ar-A

r7

Plag

iocl

ase o

r Bi

otite

FCT=

28.0

2—

—9.

140

08-B

A-6

6—

38.1

8629

−119

.056

80D

acite

of S

ilver

Hill

deb

ris

flow

clas

t9.

064

0.02

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.06

4

BH31

—38

.194

−119

.008

Dac

ite o

f Silv

er H

ill, p

lug

8.6

0.4

K-A

r3

Seric

ite-c

hlor

iteol

d*8.

8—

8.8

077-

6F—

38.1

8809

−119

.008

54D

acite

of S

ilver

Hill

-Su

garlo

af p

lug

9.08

60.

028

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

086

459

KA

-190

738

.097

−119

.064

Eure

ka V

alle

y Tu

ff9.

80.

2K

-Ar

1Bi

otite

old*

10.1

—10

.131

KA

-190

938

.247

−118

.990

Eure

ka V

alle

y Tu

ff9.

50.

3K

-Ar

1Bi

otite

old*

9.8

—9.

827

KA

-190

838

.247

−118

.990

Eure

ka V

alle

y Tu

ff9.

60.

3K

-Ar

1Bi

otite

old*

9.9

—9.

9W

24—

38.1

02−1

19.0

66Eu

reka

Val

ley

Tuff

9.19

0.28

K-A

r1

Biot

iteol

d*9.

4—

9.4

W25

—38

.131

−119

.181

Eure

ka V

alle

y Tu

ff9.

350.

37K

-Ar

1Bi

otite

old*

9.6

—9.

6W

25—

38.1

31−1

19.1

81Eu

reka

Val

ley

Tuff

9.01

0.27

K-A

r1

Biot

iteol

d*9.

2—

9.2

077-

9A—

38.2

2088

−118

.974

43Eu

reka

Val

ley

Tuff

9.40

10.

023

Ar-A

r7

Biot

iteFC

T=28

.02

——

9.40

107

7-9A

—38

.220

88−1

18.9

7443

Eure

ka V

alle

y Tu

ff9.

383

0.02

6A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.38

309

8-12

A—

38.3

5923

−119

.199

17Eu

reka

Val

ley

Tuff

9.45

0.04

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

4509

-BA

-49

—38

.263

89−1

19.0

4748

Eure

ka V

alle

y Tu

ff9.

267

0.01

9A

r-Ar

7Bi

otite

FCT=

28.0

2—

—9.

267

AU

-10/

61/D

D61

—38

.260

−118

.981

Eure

ka V

alle

y Tu

ff9.

200.

04A

r-Ar3

9Bi

otite

——

9.26

9.26

6-28

9-2

—38

.372

9−1

18.9

993

Eure

ka V

alle

y Tu

ff9.

300.

29A

r-Ar3

9Bi

otite

——

9.36

9.36

USG

S(M

)-BH

9—

38.1

57−1

19.1

16Tr

achy

ande

site o

f Mou

nt

Bied

eman

9.3

0.3

K-A

r6

Who

le ro

ckol

d*9.

5—

9.5

USG

S(M

)-MTB

1—

38.1

46−1

19.0

73Tr

achy

ande

site o

f Mou

nt

Bied

eman

9.5

0.2

K-A

r6

Hor

nble

nde

old*

9.8

—9.

8

098-

11E

—38

.110

99−1

19.1

5841

Trac

hyan

desit

e of M

ount

Bi

edem

an9.

019

0.02

8A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.01

9

09-B

A-2

2—

38.1

4302

−119

.179

74Tr

achy

ande

site o

f Mou

nt

Bied

eman

9.02

20.

024

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

022

09SB

015A

—38

.123

10−1

19.1

4843

Trac

hyan

desit

e of M

ount

Bi

edem

an8.

890

0.06

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

8.89

0

108-

12F

—38

.163

36−1

19.0

9918

Trac

hyan

desit

e of M

ount

Bi

edem

an9.

987

0.01

5A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.98

7

108-

9A—

38.1

6540

−119

.098

16Tr

achy

ande

site o

f Mou

nt

Bied

eman

9.94

70.

019

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

947

10-B

A-4

6—

38.1

7380

−119

.115

08Tr

achy

ande

site o

f Mou

nt

Bied

eman

8.77

90.

013

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

779

Tabl

e 3.

—Co

ntin

ued

Table III 17


Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

10-B

A-6

1—

38.1

4005

−119

.015

51Tr

achy

ande

site o

f Mou

nt

Bied

eman

10.0

180.

164

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.018

12-B

A-2

2—

38.1

0155

−119

.123

95Tr

achy

ande

site o

f Mou

nt

Bied

eman

8.93

30.

042

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—8.

933

6-21

5-1/

121/

72—

38.1

344

−119

.082

5Tr

achy

ande

site o

f Mou

nt

Bied

eman

9.18

0.08

Ar-A

r39

Hor

nble

nde

——

9.24

9.24

MC-

12-1

8—

38.1

5575

−119

.078

25Tr

achy

ande

site o

f Mou

nt

Bied

eman

9.24

0.09

Ar-A

r414

Hor

nble

nde

——

9.18

9.18

119-

20B

—38

.134

52−1

19.0

7613

Trac

hyan

desit

e of M

ount

Bi

edem

an, p

lug

9.07

30.

033

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

073

08-B

A-6

5—

38.3

1071

−118

.978

08Rh

yolit

e of B

ald

Peak

9.68

20.

013

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

682

10-B

A-6

7—

38.2

6203

−118

.983

03Rh

yolit

e of B

ald

Peak

9.65

20.

016

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

652

507

KA

-199

838

.154

−119

.089

Rhyo

lite o

f Bod

ie H

ills

9.5

0.3

K-A

r1

Plag

iocl

ase

old*

9.8

—9.

850

7K

A-2

049

38.1

54−1

19.0

89Rh

yolit

e of B

odie

Hill

s9.

30.

3K

-Ar

1Bi

otite

old*

9.5

—9.

5U

SGS(

M)-B

H27

—38

.140

−119

.056

Rhyo

lite o

f Bod

ie H

ills

9.1

0.2

K-A

r6

Biot

iteol

d*9.

3—

9.3

077-

7D—

38.1

6719

−119

.099

83Rh

yolit

e of B

odie

Hill

s9.

858

0.02

7A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.85

807

7-7D

—38

.167

19−1

19.0

9983

Rhyo

lite o

f Bod

ie H

ills

9.86

00.

013

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

860

088-

21C

—38

.251

34−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.77

60.

017

Ar-A

r7

Biot

iteFC

T=28

.02

——

9.77

608

8-21

C—

38.2

5134

−119

.083

82Rh

yolit

e of B

odie

Hill

s9.

893

0.02

5A

r-Ar

7Bi

otite

FCT=

28.0

2—

—9.

893

088-

21C

—38

.251

34−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.80

00.

020

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

800

088-

21C

—38

.251

34−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.80

60.

018

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

806

088-

21C

—38

.251

34−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.74

00.

023

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—9.

740

088-

21C

—38

.251

34−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.76

60.

020

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

766

088-

21C

—38

.251

34−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.77

00.

009

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

770

088-

21C

—38

.251

34−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.77

40.

008

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

774

08-B

A-5

0—

38.2

4816

−119

.096

63Rh

yolit

e of B

odie

Hill

s9.

757

0.01

3A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

9.75

709

8-10

B —

38.2

5135

−119

.083

82Rh

yolit

e of B

odie

Hill

s9.

819

0.01

3A

r-Ar

7Bi

otite

FCT=

28.0

2—

—9.

819

098-

10B

—38

.251

35−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.78

60.

022

Ar-A

r7

Biot

iteFC

T=28

.02

——

9.78

609

8-10

B (B

Hb)

—38

.251

35−1

19.0

8382

Rhyo

lite o

f Bod

ie H

ills

9.81

90.

017

Ar-A

r7

Biot

iteFC

T=28

.02

——

9.81

909

8-10

B —

38.2

5135

−119

.083

82Rh

yolit

e of B

odie

Hill

s9.

778

0.03

1A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

9.77

809

8-10

B—

38.2

5135

−119

.083

82Rh

yolit

e of B

odie

Hill

s9.

748

0.02

1A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

9.74

809

8-10

B—

38.2

5135

−119

.083

82Rh

yolit

e of B

odie

Hill

s9.

779

0.00

5A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

9.77

909

8-10

B—

38.2

5135

−119

.083

82Rh

yolit

e of B

odie

Hill

s9.

756

0.00

2A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

9.75

609

8-13

B—

38.2

6802

−119

.132

18Rh

yolit

e of B

odie

Hill

s9.

813

0.02

7A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

9.81

309

-BA

-20

—38

.156

62−1

19.0

4741

Rhyo

lite o

f Bod

ie H

ills

9.60

90.

013

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

609

09-B

A-4

7—

38.2

8409

−119

.138

21Rh

yolit

e of B

odie

Hill

s9.

877

0.01

2A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

9.87

7U

SGS(

M)-B

aghd

ad—

38.2

786

−118

.946

7Rh

yolit

e of B

odie

Cre

ek9.

90.

3K

-Ar

2Sa

nidi

neol

d*10

.2—

10.2

USG

S(M

)-Bag

hdad

—38

.278

6−1

18.9

467

Rhyo

lite o

f Bod

ie C

reek

10.2

0.4

K-A

r2

Plag

iocl

ase

old*

10.5

—10

.507

7-9B

—38

.269

71−1

18.9

5063

Rhyo

lite o

f Bod

ie C

reek

10.1

630.

029

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—10

.163

Tabl

e 3.

—Co

ntin

ued

Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

108-

11A

—38

.278

26−1

18.9

4807

Rhyo

lite o

f Bod

ie C

reek

9.89

00.

008

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—9.

890

11-B

A-3

2—

38.3

364

−118

.978

04Rh

yolit

e of B

odie

Cre

ek10

.127

0.01

3A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

10.1

2711

-BA

-60

—38

.326

93−1

18.9

7204

Rhyo

lite o

f Bod

ie C

reek

11.3

350.

138

Ar-A

r7

Feld

spar

FCT=

28.0

2—

—11

.335

077-

8C—

38.2

7145

−119

.077

83Tr

achy

ande

site o

f Aur

ora

Cany

on10

.460

0.02

0A

r-Ar

7Bi

otite

FCT=

28.0

2—

—10

.460

077-

8C#2

—38

.271

45−1

19.0

7783

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.4

810.

025

Ar-A

r7

Biot

iteFC

T=28

.02

——

10.4

81

077-

8C R

un 1

—38

.271

45−1

19.0

7783

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.4

270.

028

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.427

077-

8C R

un 2

—38

.271

45−1

19.0

7783

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.4

260.

030

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.426

077-

8C—

38.2

7145

−119

.077

83Tr

achy

ande

site o

f Aur

ora

Cany

on10

.444

0.01

4A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

10.4

44

077-

8C R

un 2

—38

.271

45−1

19.0

7783

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.4

640.

015

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—10

.464

077-

8C R

un 3

—38

.271

45−1

19.0

7783

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.4

580.

016

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—10

.458

088-

21A

—38

.273

63−1

19.1

3962

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.3

580.

025

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.358

088-

23A

—38

.278

52−1

19.1

0021

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.5

830.

032

Ar-A

r7

Biot

iteFC

T=28

.02

——

10.5

83

088-

23A

—38

.278

52−1

19.1

0021

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.2

750.

109

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.275

088-

23B

—38

.278

31−1

19.0

9908

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.5

340.

052

Ar-A

r7

Biot

iteFC

T=28

.02

——

10.5

34

088-

23B

—38

.278

31−1

19.0

9908

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.3

180.

023

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.318

088-

23D

—38

.281

13−1

19.1

0206

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.4

630.

047

Ar-A

r7

Biot

iteFC

T=28

.02

——

10.4

63

088-

23D

—38

.281

13−1

19.1

0206

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.2

650.

052

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.265

088-

25A

—38

.273

22−1

19.0

9077

Trac

hyan

desit

e of A

uror

a Ca

nyon

10.4

250.

026

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.425

10-B

A-6

2—

38.3

6327

−119

.006

35Te

phra

in se

dim

enta

ry ro

cks

of F

letc

her V

alle

y10

.464

0.04

1A

r-Ar

7Bi

otite

FCT=

28.0

2—

—10

.464

10-B

A-6

2—

38.3

6327

−119

.006

35Fl

etch

er V

alle

y se

dim

ents

10.5

820.

023

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.582

077-

9E—

38.3

1905

−118

.910

03Tr

achy

ande

site o

f Del

Mon

te10

.949

0.02

5A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

10.9

4908

SB03

8—

38.4

0828

−118

.973

83Tr

achy

ande

site o

f Del

Mon

te10

.982

0.05

0A

r-Ar

7Bi

otite

FCT=

28.0

2—

—10

.982

11-B

A-4

1—

38.3

5057

−118

.980

85Tr

achy

ande

site o

f Del

Mon

te10

.942

0.02

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

10.9

4209

8-11

B—

38.1

2451

−119

.171

26Tr

achy

daci

te o

f Brid

gepo

rt Ca

nyon

11.0

670.

022

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—11

.067

Tabl

e 3.

—Co

ntin

ued

Table III 19


Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

09SB

020A

—38

.132

30−1

19.1

3277

Trac

hyda

cite

of B

ridge

port

Cany

on11

.080

0.01

9A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

11.0

80

08SB

032

—38

.345

61−1

18.9

5580

Unw

elde

d tu

ff in

sedi

men

tary

ro

cks o

f Fle

tche

r Val

ley

10.9

180.

043

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—10

.918

10-B

A-5

—38

.339

45−1

18.9

9699

Pyro

xene

rhyo

lite

11.1

530.

011

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—11

.153

10-B

A-2

7—

38.2

7500

−118

.904

98Rh

yolit

e of E

ast B

raw

ley

Peak

11.1

790.

016

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—11

.179

USG

S(M

)-NTS

10B

—38

.302

1−1

18.8

967

Rhyo

lite o

f Aur

ora C

reek

10.9

0.2

K-A

r2

Biot

iteol

d*11

.2—

—U

SGS(

M)-N

TS10

B—

38.3

021

−118

.896

7Rh

yolit

e of A

uror

a Cre

ek11

.00.

2K

-Ar

2Sa

nidi

neol

d*11

.3—

—10

-BA

-20

—38

.316

79−1

18.9

1129

Rhyo

lite o

f Aur

ora C

reek

11.1

770.

013

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—11

.177

10-B

A-2

1—

38.3

0315

−118

.897

40Rh

yolit

e of A

uror

a Cre

ek11

.181

0.02

2A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

11.1

8107

7-9D

—38

.285

62−1

18.9

2803

Rhyo

lite o

f Del

Mon

te

Cany

on11

.200

0.03

2A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

11.2

00

077-

9D—

38.2

8562

−118

.928

03Rh

yolit

e of D

el M

onte

Ca

nyon

11.1

390.

020

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—11

.139

AU

-6/6

0/D

D61

—38

.285

−118

.928

Rhyo

lite o

f Del

Mon

te

Cany

on11

.21

0.03

Ar-A

r39

Biot

ite—

—11

.28

11.2

8

USG

S(M

)-710

-7—

38.2

822

−118

.928

1Rh

yolit

e of D

el M

onte

Ca

nyon

?11

.20.

2K

-Ar

2Bi

otite

old*

11.5

—11

.5

077-

9C—

38.2

7661

−118

.930

36Rh

yolit

e of D

el M

onte

Ca

nyon

11.2

580.

142

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—11

.258

077-

9C—

38.2

7661

−118

.930

36Rh

yolit

e of D

el M

onte

Ca

nyon

11.2

200.

017

Ar-A

r7

Sani

dine

FCT=

28.0

2—

—11

.220

077-

8B—

38.2

8334

−119

.056

17Tr

achy

daci

te in

trusio

n11

.153

0.02

8A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

11.1

5309

-BA

-35

—38

.290

48−1

19.0

4642

Trac

hyda

cite

intru

sion

11.2

690.

034

Ar-A

r7

Biot

iteFC

T=28

.02

——

11.2

6909

8-13

D—

38.2

7655

−119

.160

62Tr

achy

ande

site o

f Cla

rk

Cany

on11

.341

0.01

7A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

11.3

41

09-B

A-4

3—

38.2

6358

−119

.168

25Tr

achy

ande

site o

f Cla

rk

Cany

on11

.268

0.11

2A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

11.2

68

KA

2379

R—

38.4

133

−118

.941

7Tu

ff in

Ald

rich

Stat

ion

Form

a-tio

n11

.40

0.54

K-A

r11

Biot

iteol

d*11

.70

—11

.70

547

KA

-204

838

.255

−118

.948

Trac

hyan

desit

e of W

est B

raw

-le

y Pe

ak12

.50.

2K

-Ar

1Pl

agio

clas

eol

d*12

.8—

12.8

USG

S(M

)-712

-1—

38.2

522

−118

.917

5Tr

achy

ande

site o

f Wes

t Bra

w-

ley

Peak

11.2

0.2

K-A

r2

Biot

iteol

d*11

.5—

11.5

USG

S(M

)-712

-1—

38.2

522

−118

.917

5Tr

achy

ande

site o

f Wes

t Bra

w-

ley

Peak

10.9

0.3

K-A

r2

Plag

iocl

ase

old*

11.2

—11

.2

USG

S(M

)-712

-1—

38.2

522

−118

.917

5Tr

achy

ande

site o

f Wes

t Bra

w-

ley

Peak

11.6

0.3

K-A

r2

Hor

nble

nde

old*

11.9

—11

.9

077-

7G—

38.2

3439

−118

.966

71Tr

achy

ande

site o

f Wes

t Bra

w-

ley

Peak

11.3

230.

032

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—11

.323

Tabl

e 3.

—Co

ntin

ued

Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

108-

10C

—38

.280

52−1

18.9

0623

Trac

hyan

desit

e of W

est B

raw

-le

y Pe

ak11

.514

0.01

9A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

11.5

14

6—

38.1

256

−119

.169

7Ba

salti

c tra

chya

ndes

ite o

f Ra

nche

ria11

.30.

9K

-Ar

4W

hole

rock

old*

11.6

—11

.6

742-

45—

38.0

869

−119

.143

1Ba

salti

c tra

chya

ndes

ite o

f Ra

nche

ria11

.70.

5K

-Ar

12W

hole

rock

new

——

11.7

MC-

12-2

0—

38.2

7010

−119

.126

10H

ornb

lend

e tra

chya

ndes

ite

intru

sion

11.9

0.20

Ar-A

r414

Hor

nble

nde

——

11.8

211

.82

098-

11A

—38

.122

39−1

19.1

6954

Tuff

of Ja

cks S

prin

g12

.069

0.01

5A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

12.0

6909

-BA

-23

—38

.128

51−1

19.1

7491

Tuff

of Ja

cks S

prin

g12

.044

0.01

5A

r-Ar

7Sa

nidi

neFC

T=28

.02

——

12.0

446-

181-

12/5

2/D

D72

—38

.119

3−1

19.1

039

Tuff

of Ja

cks S

prin

g11

.87

0.16

Ar-A

r39

Sani

dine

——

11.9

511

.95

6-18

1-12

/53/

DD

72—

38.1

193

−119

.103

9Tu

ff of

Jack

s Spr

ing

11.9

00.

14A

r-Ar3

9Sa

nidi

ne—

—11

.98

11.9

8K

A23

62—

38.4

408

−118

.972

5H

ornb

lend

e and

esite

12.1

10.

39K

-Ar

11Pl

agio

clas

eol

d12

.43

—12

.43

KA

2364

—38

.440

8−1

18.9

725

Hor

nble

nde a

ndes

ite12

.07

0.50

K-A

r11

Hor

nble

nde

old

12.3

9—

12.3

9K

A23

68—

38.4

408

−118

.972

5H

ornb

lend

e and

esite

12.3

30.

31K

-Ar

11Bi

otite

old

12.6

6—

12.6

610

-BA

-29

—38

.364

66−1

19.0

1452

Trac

hyda

cite

of R

ough

Cre

ek11

.675

0.01

6A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

11.6

7510

-BA

-6—

38.3

3375

−119

.024

70Tr

achy

daci

te o

f Rou

gh C

reek

12.9

450.

020

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—12

.945

11-B

A-4

0—

38.4

1155

−119

.019

07Tr

achy

daci

te o

f Rou

gh C

reek

12.8

040.

023

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—12

.804

07-B

A-3

8—

38.3

6049

−119

.145

02A

ndes

ite o

f Lak

evie

w S

prin

g12

.930

0.03

3A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

12.9

30U

SGS(

M)-7

11-6

7—

38.2

894

−118

.909

2Tr

achy

ande

site o

f Aur

ora

13.5

0.3

K-A

r2

Hor

nble

nde

old*

13.9

—13

.9U

SGS(

M)-6

68-G

10—

38.2

403

−118

.891

7Tr

achy

ande

site o

f Aur

ora

14.4

0.3

K-A

r2

Hor

nble

nde

old*

14.8

—U

SGS(

M)-7

11-8

—38

.268

1−1

18.8

917

Trac

hyan

desit

e of A

uror

a15

.40.

3K

-Ar

2Pl

agio

clas

eol

d*15

.8—

15.8

CH8Z

1—

38.2

88−1

18.8

82Tr

achy

ande

site o

f Aur

ora

10.9

0.3

K-A

r5

Who

le ro

ckne

w—

—10

.910

8-10

A—

38.2

7293

−118

.912

72Tr

achy

ande

site o

f Aur

ora

12.5

800.

024

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—12

.580

00-B

A-1

6—

38.2

708

−118

.890

8Tr

achy

ande

site o

f Aur

ora

13.0

50.

44A

r-Ar3

9H

ornb

lend

e—

—13

.13

13.1

300

-BA

-26

—38

.254

2−1

18.8

841

Trac

hyan

desit

e of A

uror

a13

.05

0.08

Ar-A

r39

Hor

nble

nde

——

13.1

313

.13

098-

12E

—38

.391

43−1

19.1

2397

Trac

hyan

desit

e of M

ason

ic

Gul

ch13

.441

0.02

6A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

13.4

41

MA

S10-

72—

38.4

0189

−119

.137

18Tr

achy

ande

site o

f Mas

onic

G

ulch

13.4

850.

017

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—13

.485

MA

S10-

73—

38.3

9643

−119

.134

70Tr

achy

ande

site o

f Mas

onic

G

ulch

13.4

670.

016

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—13

.467

MA

S10-

75—

38.3

9169

−119

.115

49Tr

achy

ande

site o

f Mas

onic

G

ulch

<13.

497

0.02

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

<13.

497

12-B

A-9

—38

.336

81−1

19.0

7377

Trac

hyda

cite

of E

ast C

anyo

n13

.782

0.02

5A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

13.7

825

—38

.097

8−1

19.1

475

Trac

hyan

desit

e of S

inna

mon

Cu

t13

.30.

4K

-Ar

4H

ornb

lend

eol

d*13

.7—

13.7

12-B

A-3

—38

.349

74−1

18.8

4729

Trac

hyan

desit

e of M

ud S

prin

g Ca

nyon

13.9

60.

11A

r-Ar4

14Pl

agio

clas

e—

—13

.87

13.8

7

10-B

A-9

—38

.352

78−1

19.0

2068

Trac

hyan

desit

e of M

ason

ic,

plug

14.9

980.

019

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—14

.998

Tabl

e 3.

—Co

ntin

ued

Table III 21


Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

MA

S10-

76—

38.3

8169

−119

.115

34Tr

achy

ande

site o

f Mas

onic

, pl

ug14

.190

0.02

1A

r-Ar

7H

ornb

lend

eFC

T=28

.02

——

14.1

90

088-

22B

—38

.379

37−1

19.0

7802

Trac

hyan

desit

e of M

ason

ic14

.067

0.08

1A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

14.0

6708

8-23

F—

38.3

1068

−119

.117

00Tr

achy

ande

site o

f Mas

onic

14.1

930.

039

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—14

.193

08-B

A-6

2—

38.3

2006

−119

.049

43Tr

achy

ande

site o

f Mas

onic

14.1

310.

030

Ar-A

r7

Plag

iocl

ase

FCT=

28.0

2—

—14

.131

098-

12B

—38

.387

62−1

19.1

8139

Trac

hyan

desit

e of M

ason

ic14

.715

0.02

5A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

14.7

1509

8-12

D—

38.3

9951

−119

.119

39Tr

achy

ande

site o

f Mas

onic

<14.

800.

02A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

<14.

8009

8-12

F—

38.3

7542

−119

.114

18Tr

achy

ande

site o

f Mas

onic

14.0

940.

017

Ar-A

r7

Hor

nble

nde

FCT=

28.0

2—

—14

.094

09-B

A-7

—38

.337

86−1

19.0

8727

Trac

hyan

desit

e of M

ason

ic14

.674

0.02

5A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

14.6

7410

-BA

-13

—38

.351

54−1

19.1

0419

Trac

hyan

desit

e of M

ason

ic14

.410

0.01

6A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

14.4

1010

-BA

-15

—38

.341

30−1

19.1

1570

Trac

hyan

desit

e of M

ason

ic14

.141

0.01

7A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

14.1

4110

-BA

-69

—38

.305

37−1

19.1

3652

Trac

hyan

desit

e of M

ason

ic14

.107

0.01

4A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

14.1

0712

-BA

-20

—38

.334

10−1

19.1

5949

Trac

hyan

desit

e of M

ason

ic14

.136

0.02

0A

r-Ar

7Pl

agio

clas

eFC

T=28

.02

——

14.1

36M

C-12

-19

—38

.319

52−1

18.7

8154

Trac

hyan

desit

e of B

orea

lis16

.06

0.10

Ar-A

r414

Hor

nble

nde

——

15.9

615

.96

FA1

—38

.293

1−1

18.8

914

Alte

ratio

n: A

uror

a 10

.04

0.03

Ar-A

r310

Adu

laria

——

10.1

010

.10

FA66

—38

.237

5−1

18.9

008

Alte

ratio

n: E

ast B

raw

ley

Peak

al

tera

tion

zone

12

.34

0.04

Ar-A

r310

Alu

nite

——

12.4

212

.42

PP09

-10A

1—

38.2

5309

−119

.138

44A

ltera

tion:

Aur

ora C

anyo

n al

tera

tion

zone

10.8

650.

065

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—10

.865

USG

S(M

)-734

6-1

—38

.215

−119

.004

Alte

ratio

n: B

odie

, Sta

ndar

d H

ill7.

20.

1K

-Ar

6A

dula

riaol

d*7.

4—

7.4

USG

S(M

)-734

6-1

—38

.215

−119

.004

Alte

ratio

n: B

odie

, Sta

ndar

d H

ill7.

00.

1K

-Ar

6A

dula

riaol

d*7.

2—

7.2

USG

S(M

)-RCD

1B—

38.2

01−1

19.0

05A

ltera

tion:

Bod

ie, R

ed C

loud

m

ine

7.7

0.1

K-A

r6

Adu

laria

old*

7.9

—7.

9

USG

S(M

)-B27

0—

38.2

16−1

19.0

04A

ltera

tion:

Bod

ie, S

tand

ard

Hill

8.0

0.2

K-A

r6

Adu

laria

old*

8.2

—8.

2

077-

6A—

38.2

149

−119

.003

7A

ltera

tion:

Bod

ie, s

outh

of

Bodi

e Blu

ff8.

286

0.02

4A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.28

6

077-

6C—

38.2

187

−119

.000

5A

ltera

tion:

Bod

ie, B

odie

Blu

ff7.

179

0.41

7A

r-Ar

7A

dula

riaFC

T=28

.02

——

7.17

911

-BA

-7G

—38

.204

20−1

19.0

0649

Alte

ratio

n: B

odie

, Silv

er H

ill8.

217

0.01

2A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.21

711

-BA

-21

—38

.203

70−1

19.0

0919

Alte

ratio

n: B

odie

, Red

Clo

ud

min

e8.

124

0.00

6A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.12

4

BOD

09-5

—38

.204

30−1

19.0

0660

Alte

ratio

n: B

odie

, Oro

min

e du

mp

8.47

30.

007

Ar-A

r7

Adu

laria

FCT=

28.0

2—

—8.

473

BOD

09-3

—38

.201

46−1

19.0

048

Alte

ratio

n: B

odie

, Red

Clo

ud

min

e8.

628

0.01

4A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.62

8

09-B

A-2

8I—

38.2

015

−119

.003

6A

ltera

tion:

Bod

ie, R

ed C

loud

m

ine

8.85

20.

013

Ar-A

r7

Adu

laria

FCT=

28.0

2—

—8.

852

11-B

A-2

2—

38.2

1257

−119

.004

02A

ltera

tion:

Bod

ie, s

outh

of

Bodi

e Blu

ff8.

498

0.00

5A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.49

8

Tabl

e 3.

—Co

ntin

ued

Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

AU

-18/

65/D

D61

—38

.201

−119

.004

Alte

ratio

n: B

odie

, Red

Clo

ud

min

e8.

410.

02A

r-Ar3

9A

dula

ria—

—8.

468.

46

AU

-17/

64/D

D61

—38

.215

−118

.997

Alte

ratio

n: B

odie

, sou

th o

f Bo

die B

luff

8.23

0.04

Ar-A

r39

Adu

laria

——

8.28

8.28

AU

-16/

63/D

D61

—38

.215

−119

.004

Alte

ratio

n: B

odie

, sou

th o

f Bo

die B

luff

8.33

0.02

Ar-A

r39

Adu

laria

——

8.38

8.38

SAW

11-9

—39

.290

36−1

18.9

1657

Alte

ratio

n: S

awto

oth

alte

ra-

tion

zone

11

.105

0.01

1A

r-Ar

7A

luni

teFC

T=28

.02

——

11.1

05

3950

9-3K

—38

.207

93−1

19.2

2751

Alte

ratio

n: H

wy

395

alte

ratio

n zo

ne8.

169

0.01

3A

r-Ar

7A

luni

teFC

T=28

.02

——

8.16

9

08-B

A-4

6—

38.2

4430

−119

.103

85A

ltera

tion:

Pot

ato

Peak

alte

ra-

tion

zone

, Alta

Pin

a min

e10

.769

0.03

4A

r-Ar

7A

luni

teFC

T=28

.02

——

10.7

69

MA

S09-

1—

38.3

5783

−119

.132

68A

ltera

tion:

Mas

onic

, Red

Ro

ck m

ine

13.2

690.

144

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—13

.269

MA

S09-

1A—

38.3

5847

−119

.138

24A

ltera

tion:

Mas

onic

, Red

Ro

ck m

ine

13.4

710.

038

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—13

.471

MA

S07-

1A—

38.3

4992

−119

.148

32A

ltera

tion:

Mas

onic

, Ch

emun

g m

ine

13.3

860.

068

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—13

.386

088-

22A

—38

.367

31−1

19.1

0727

Alte

ratio

n: M

ason

ic,

May

belle

min

e13

.018

0.06

1A

r-Ar

7A

luni

teFC

T=28

.02

——

13.0

18

07-B

A-4

0—

38.3

6544

−119

.116

07A

ltera

tion:

Mas

onic

, Pi

ttsbu

rg-L

iber

ty m

ine

13.0

270.

049

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—13

.027

MA

S10-

55—

38.4

1419

−119

.102

59A

ltera

tion:

Mas

onic

, Red

was

h al

tera

tion

zone

13.2

70.

02A

r-Ar

7A

luni

teFC

T=28

.02

——

13.2

7

RW08

-1—

38.4

1123

−119

.124

14A

ltera

tion:

Mas

onic

, Red

was

h al

tera

tion

zone

13.3

380.

035

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—13

.338

MA

S07-

3—

38.3

5968

−119

.126

82A

ltera

tion:

Mas

onic

, Sar

ita

min

e13

.253

0.05

1A

r-Ar

7A

luni

teFC

T=28

.02

——

13.2

53

CC09

-9D

1—

38.1

9869

−119

.170

50A

ltera

tion:

Cin

naba

r Can

yon

alte

ratio

n zo

ne8.

824

0.29

4A

r-Ar

7A

luni

teFC

T=28

.02

——

8.82

4

CC09

-9D

2—

38.1

9869

−119

.170

50A

ltera

tion:

Cin

naba

r Can

yon

alte

ratio

n zo

ne8.

682

0.02

0A

r-Ar

7A

luni

teFC

T=28

.02

——

8.68

2

MA

S11-

1A—

38.3

6041

−119

.083

69A

ltera

tion:

Mas

onic

, Per

ini

min

e12

.956

0.02

0A

r-Ar

7A

luni

teFC

T=28

.02

——

12.9

56

MA

S11-

2B—

38.3

6064

−119

.086

81A

ltera

tion:

Mas

onic

, Per

ini

min

e12

.960

0.01

4A

r-Ar

7A

luni

teFC

T=28

.02

——

12.9

60

AU

R10-

3—

38.2

3752

−118

.899

19A

ltera

tion:

Eas

t Bra

wle

y Pe

ak

alte

ratio

n zo

ne

11.9

540.

016

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—11

.954

BOD

11-4

E—

38.2

1257

−119

.004

02A

ltera

tion:

Bod

ie, S

tand

ard

Hill

min

e8.

425

0.00

3A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.42

5

Tabl

e 3.

—Co

ntin

ued

Table III 23


Sam

ple

num

ber

Lab_

no.

Latit

ude

Long

itude

Uni

tA

ge, M

aEr

ror,

Ma

Met

hod

Sour

ce1

Min

eral

Dec

ay

cons

tant

2

Reca

lcul

ated

ag

e,

usin

g ne

w

deca

y co

nsta

nts

Age

re

calc

ulat

ed

for F

CT=2

8.02

M

a

Sum

mar

y ag

e

MA

S12-

10 (#

1)—

38.3

3716

−119

.160

13A

ltera

tion:

Mas

onic

, Suc

cess

m

ine

13.3

980.

081

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—13

.398

MA

S12-

10 (#

2)—

38.3

3716

−119

.160

13A

ltera

tion:

Mas

onic

, Suc

cess

m

ine

13.6

380.

077

Ar-A

r7

Alu

nite

FCT=

28.0

2—

—13

.638

37—

38.2

87−1

18.8

87A

ltere

d tra

chya

ndes

ite o

f A

uror

a10

.30.

2K

-Ar

4A

dula

riaol

d*10

.6—

10.6

AU

-1/5

8/D

D61

—38

.266

−118

.900

Alte

ratio

n: A

uror

a, Es

mer

alda

ve

in10

.63

0.05

Ar-A

r59

K-fe

ldsp

ar—

—10

.70

10.7

0

AU

-2/5

9/D

D61

—38

.282

−118

.896

Alte

ratio

n: A

uror

a, D

el M

onte

sh

aft

10.2

80.

05A

r-Ar5

9K

-feld

spar

——

10.3

510

.35

BOD

11-3

A—

38.2

1961

−119

.003

54A

ltera

tion:

Bod

ie, U

pper

H

obar

t Tun

nel

8.19

40.

005

Ar-A

r7

Adu

laria

FCT=

28.0

2—

—8.

194

BOD

11-3

B—

38.2

1961

−119

.003

54A

ltera

tion:

Bod

ie B

luff,

In

clin

e vei

n8.

542

0.02

5A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.54

2

12-B

A-1

7—

38.2

1961

−119

.000

19A

ltera

tion:

Bod

ie B

luff,

wes

t sid

e8.

357

0.02

8A

r-Ar

7A

dula

riaFC

T=28

.02

——

8.35

7

1 Sou

rces

: 1, G

ilber

t and

oth

ers (

1968

); 2,

Silb

erm

an a

nd M

cKee

(197

2); 3

, Silb

erm

an a

nd o

ther

s (19

72);

4, K

lein

ham

pl a

nd o

ther

s (19

75);

5, M

orto

n an

d ot

hers

(197

7); 6

, Silb

erm

an a

nd C

hest

erm

an (1

972)

; 7,

R.J

Flec

k, th

is re

port;

8, L

ange

and

oth

ers (

1993

); 9,

L.W

. Sne

e, th

is re

port;

10,

Bre

it, (2

000)

; 11,

Gilb

ert a

nd R

eyno

lds (

1973

); 12

, Mar

vin

and

Dob

son

(197

9); 1

3, R

ehei

s and

oth

ers (

2002

); 14

, M.A

. Cos

ca, t

his

repo

rt.2 O

ld*:

All

ages

with

this

not

atio

n ad

just

ed in

“R

ecal

cula

ted

age”

col

umn

to a

ccou

nt fo

r new

dec

ay c

onst

ants

of S

teig

er a

nd Jä

ger (

1977

).3 A

ge in

itial

ly c

alcu

late

d fo

r Fis

h C

anyo

n tu

ff=27

.84

Ma.

4 Age

initi

ally

cal

cula

ted

for F

ish

Can

yon

Tuff=

28.2

01 M

a.5 A

ge in

itial

ly c

alcu

late

d fo

r Fis

h C

anyo

n tu

ff=27

.84

Ma;

isoc

hron

age

.6 L

ikel

y an

inac

cura

te a

ge.

Tabl

e 3.

—Co

ntin

ued

References Cited 25

References Cited

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Breit, F.J., Jr., 2000, Structural and temporal relationships and geochemical characteristics of the East Brawley Peak acid-sulfate prospect and the adjacent Aurora adularia-sericite system: Reno, University of Nevada, M.S. thesis, 215 p.

Busby, C.J., 2013, Birth of a plate boundary at ca. 12 Ma in the Ancestral Cascades arc, Walker Lane belt of California and Nevada: Geosphere, v. 9, p. 1147–1160.

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Menlo Park Publishing Service Centers, California Manuscript approved for publication January 23, 2015Edited by Sarah NagorsenDesign and Layout by Cory Hurd

Fleck and others—G

eochronology of Cenozoic Rocks in the Bodie H

ills, California and Nevada—

Data Series 916

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