2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 343-11
Presentation Time: 4:00 PM

40AR/39AR AND U-PB AGES OF SILICIC IGNIMBRITES, CALDERAS, AND GRANITIC PLUTONS, SOUTHERN STILLWATER RANGE AND CLAN ALPINE MOUNTAINS, NEVADA: LINKAGES BETWEEN VOLCANIC AND PLUTONIC ROCKS


JOHN, David A., U.S. Geological Survey, Menlo Park, CA 94025, HENRY, Christopher D., Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV 89557, COLGAN, Joseph P., U.S. Geological Survey, Denver Federal Center, Lakewood, CO 80225 and WATTS, Kathryn E., U.S. Geological Survey, 345 Middlefield Rd. MS 973, Menlo Park, CA 94025

Faulted calderas in the southern Stillwater Range (SSR) and Clan Alpine Mountains (CAM) reflect intense ~30 to 25 Ma magmatism related to the middle Cenozoic ignimbrite flareup. New geologic mapping, geochemistry, and 40Ar/39Ar and SHRIMP U-Pb zircon dating document 4 nested calderas and related granitoid plutons in sections up to 10 km thick that have been tilted 40->90°.

Cenozoic magmatism in SSR began with eruption of 30(?) Ma rhyolite lava domes. These are overlain by up to 1.5 km of altered intermediate lavas and breccias (29.4±0.4 Ma, U-Pb) that underlie and are inferred to be related to the Job Canyon caldera (JCC). JCC is filled by 2 km of altered rhyolite tuff of Job Canyon (29.4±0.5 Ma, U-Pb), which is overlain by up to 2.5 km of intermediate lavas (59-69% SiO2; 28.5±0.4 Ma, U-Pb; 28.79±0.03 Ma, biotite Ar-Ar). JCC is intruded by the geochemically similar IXL pluton (59-69% SiO2; 28.9±0.4 Ma, U-Pb), which is >4-5 km thick.

Magmatism resumed with eruption of rhyolite lava domes and dikes (25.6±0.3 and 25.5±0.4 Ma, U-Pb), followed by 3 thick ignimbrite units in 3 calderas: tuff of the Louderback Mountains (Tlm; low silica rhyolite; ≥600 m thick; 25.23±0.02 Ma, sanidine Ar-Ar; 25.4±0.2 Ma, U-Pb); tuff of Poco Canyon (Tpc; high-silica rhyolite; up to 4.3 km thick; 25.27±0.05 Ma, 8 sanidine Ar-Ar ages; 26.0±0.2 to 25.7±0.2 Ma, 3 U-Pb ages); and tuff of Elevenmile Canyon (trachydacite to rhyolite; up to 4.5 km thick; 25.12±0.01 Ma, 20 sanidine Ar-Ar ages; 25.7±0.4 to 25.1±0.3 Ma, 4 U-Pb ages). Ages and distribution of calderas indicate nearly simultaneous eruption of Tpc from SSR and Tlm from CAM. The tuff of Elevenmile Canyon (≥2000 km3) fills the much larger Elevenmile Canyon caldera (ECC; now ~15-40 by 45 km) that encompasses most of the SSR and CAM. In the SSR, the composite Freeman Creek pluton (granodiorite, 25.0±0.2 Ma, U-Pb; granite, 24.8±0.4 Ma, U-Pb) intrudes ECC and the Poco Canyon caldera, and at Chalk Mountain, rhyolite porphyry (25.2±0.2 Ma, U-Pb) and granite (24.8±0.3 Ma, U-Pb) plutons intrude the SW margin of ECC.

Field, geochronologic, and geochemical data show that thick plutons (>2-5 km) underlie compositionally and temporally related caldera-filling ignimbrites and indicate that focused silicic magmatism in SSR-CAM from ~30 to 25 Ma entirely replaced the Mesozoic upper crust with Oligocene rocks to depths of >5 to 10 km.

Session No. 343

T216. Cenozoic Magmatism and Volcanism in the North American Cordillera
Wednesday, 22 October 2014: 1:00 PM-5:00 PM
306 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.826
© Copyright 2014 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.
Back to: T216. Cenozoic Magmatism and Volcanism in the North American Cordillera
<< Previous Abstract | Next Abstract >>