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Open-File Report 2010-1016

Prepared in cooperation with the National Park Service

Geophysical Characterization of Range-Front Faults, Snake Valley, Nevada

By Theodore H. Asch and Donald S. Sweetkind

Abstract

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In September 2009, the U.S. Geological Survey, in cooperation with the National Park Service, collected audiomagnetotelluric (AMT) data along two profiles on the eastern flank of the Snake Range near Great Basin National Park to refine understanding of the subsurface geology. Line 1 was collected along Baker Creek, was approximately 6.7-km long, and recorded subsurface geologic conditions to approximately 800-m deep. Line 2, collected farther to the southeast in the vicinity of Kious Spring, was 2.8-km long, and imaged to depths of approximately 600 m. The two AMT lines are similar in their electrical response and are interpreted to show generally similar subsurface geologic conditions. The geophysical response seen on both lines may be described by three general domains of electrical response: (1) a shallow (mostly less than 100-200-m deep) domain of highly variable resistivity, (2) a deep domain characterized by generally high resistivity that gradually declines eastward to lower resistivity with a steeply dipping grain or fabric, and (3) an eastern domain in which the resistivity character changes abruptly at all depths from that in the western domain. The shallow, highly variable domain is interpreted to be the result of a heterogeneous assemblage of Miocene conglomerate and incorporated megabreccia blocks overlying a shallowly eastward-dipping southern Snake Range detachment fault. The deep domain of generally higher resistivity is interpreted as Paleozoic sedimentary rocks (Pole Canyon limestone and Prospect Mountain Quartzite) and Mesozoic and Cenozoic plutonic rocks occurring beneath the detachment surface. The range of resistivity values within this deep domain may result from fracturing adjacent to the detachment, the presence of Paleozoic rock units of variable resistivities that do not crop out in the vicinity of the lines, or both. The eastern geophysical domain is interpreted to be a section of Miocene strata at depth, overlain by Quaternary alluvial fill. These deposits lie east of a steeply east-dipping normal fault that cuts all units and has about 100 m of east-side-down offset.

First posted February 22, 2010

For additional information contact:

Team Chief Scientist,
USGS Crustal Imaging and Characterization
Box 25046, Mail Stop 964
Denver, CO 80225

http://crustal.usgs.gov/

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Suggested citation:

Asch, T.H., Sweetkind, D.S., 2010, Geophysical characterization of range-front faults, Snake Valley, Nevada: U.S. Geological Survey Open-File Report 2010-1016, 226 p.



Contents

Introduction

Geologic Setting

Electrical Rock Properties

Magnetotellurics

Snake Valley Audio-Magnetotelluric Survey

Audio-Magnetotelluric Data Processing

2-D Modeling Analysis of the Audio-Magnetotelluric Data

Discussion

Summary and Conclusions

References Cited


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