Timing of detachment faulting in the Bullfrog Hills and Bare Mountain area, southwest Nevada: Inferences from 40Ar/39Ar, K-Ar, U-Pb and fission track thermochronology

Hoisch, Thomas D. and Heizler, Matthew T. and Zartman, Robert E. (1997) Timing of detachment faulting in the Bullfrog Hills and Bare Mountain area, southwest Nevada: Inferences from 40Ar/39Ar, K-Ar, U-Pb and fission track thermochronology. Journal of Geophysical Research, 102 (B2). pp. 2815-2833. ISSN 0148-0227

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Abstract

Crustal extension in the Bullfrog Hills and Bare Mountain area of southwest Nevada is associated with movement along a regional detachment fault. Normal faulting in the upper plate and rapid cooling (denudation) of the lower plate were coeval with Miocene silicic volcanism and with west-northwest transport along the detachment fault. A west-northwest progression of tilting along upper plate normal faults is indicated by ages of the volcanic rocks in relation to angular unconformities. Near the breakaway, tilting in the upper plate occurred between 12.7 and 11.6 Ma, continued less strongly past 10.7 Ma, and was over by 8.2 Ma. Ten to 20 km west of the breakaway, tilting occurred between 10.7 and 10.33 Ma, continued less strongly after 10.33 Ma, and was over by 8.1 Ma. The cooling histories of the lower plate metamorphic rocks were determined by thermochronologic dating methods: K-Ar and Ar-40/(39)A on muscovite, biotite, and hornblende, Ar-40/(39)A on K-feldspar, U-Pb on apatite, zircon, and sphene, and fission track on apatite, zircon, and sphene. Lower plate rocks 10 km west of the breakaway cooled slowly from Early Cretaceous lower-amphibolite facies conditions through 350+/-50 degrees to 300+/-50 degrees C between 57 and 38 Ma, then cooled rapidly from 205+/-50 degrees to 120+/-5O degrees C between 12.6+/-1.6 and 11.1+/-1.9 Ma. Lower plate rocks 20 km west of the breakaway cooled slowly from Early Cretaceous upper-amphibolite facies conditions through 500+/-50 degrees C at 78-67 Ma, passed through 350+/-50 degrees to 300+/-50 degrees C between 16.3+/-0.4 and 10.5+/-0.3 Ma, then cooled rapidly from 285+/-50 degrees to 120+/-50 degrees C between 10.2 and 8.6 Ma. Upper plate tilting and rapid cooling (denudation) of the lower plate occurred simultaneously in the respective areas. The early slow-cooling part of the lower plate thermal histories was probably related to erosion at the Earth's surface, which stripped off about 9 km of material in 50 to 100 m.y. The results indicate an initial fault dip greater than or equal to 30 degrees and a 12 mm yr(-1) west-northwest migration of the locus of rapid tilting in the upper plate.

Item Type:	Article
Publisher’s Statement:	© 1997 by the American Geophysical Union. 10.1029/96JB03220
ID number or DOI:	10.1029/96JB03220
Keywords:	03; 16; absolute age; alkali feldspar; alkali feldspars; amphibole group; angle normal faults; Apatite; Ar/Ar; Bare Mountain; Biotite; Bullfrog Hills; Cenozoic; chain silicates; clinoamphibole; cooling; dates; death-valley; denudation; detachment faults; diffusion domains; east humboldt range; faults; feldspar group; fission-track dating; framework silicates; Funeral Mountains; Geochronology; hornblende; K/Ar; K-feldspar; metamorphic core complex; mica group; Miocene; muscovite; Neogene; nesosilicates; Nevada; normal faults; orthosilicates; phosphates; sheet silicates; Silicates; southeastern california; Structural geology; tectonic implications; Tertiary; thermal history; tilt; titanite; titanite group; United States; U/Pb; west central arizona; Zircon; zircon group
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Faculty/Staff
Department/Unit:	College of Engineering, Forestry, and Natural Science > School of Earth Sciences and Environmental Sustainability
Date Deposited:	12 Oct 2015 15:33
URI:	http://openknowledge.nau.edu/id/eprint/1366

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