USGS home page

Magnetotelluric Study of the Pahute Mesa and Oasis Valley Regions, Nye County, Nevada

by

Clifford J. Schenkel1, Thomas G. Hildenbrand1, and Gary L. Dixon2

U.S. Geological Survey Open-File Report 99-355
Version 1.0

Prepared in cooperation with the
U.S. DEPARTMENT OF ENERGY
NEVADA OPERATIONS OFFICE
(Interagency Agreement DE-AI08-96NV11967)

1999

U.S. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY
Charles G. Groat, Director

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

1Menlo Park, California 94025
2Las Vegas, Nevada 89119

minimap

This online publication consists of an Adobe Acrobat PDF file, the abstract for which is reproduced below. The data for this publication total 1.1 MB

Abstract

Magnetotelluric data delineate distinct layers and lateral variations above the pre-Tertiary basement. On Pahute Mesa, three resistivity layers associated with the volcanic rocks are defined: a moderately resistive surface layer, an underlying conductive layer, and a deep resistive layer. Considerable geologic information can be derived from the conductive layer which extents from near the water table down to a depth of approximately 2 km. The increase in conductivity is probably related to zeolite zonation observed in the volcanic rock on Pahute Mesa, which is relatively impermeable to groundwater flow unless fractured. Inferred faults within this conductive layer are modeled on several profiles crossing the Thirsty Canyon fault zone. This fault zone extends from Pahute Mesa into Oasis Valley basin. Near Colson Pond where the basement is shallow, the Thirsty Canyon fault zone is several (~2.5) kilometers wide. Due to the indicated vertical offsets associated with the Thirsty Canyon fault zone, the fault zone may act as a barrier to transverse (E-W) groundwater flow by juxtaposing rocks of different permeabilities.

We propose that the Thirsty Canyon fault zone diverts water southward from Pahute Mesa to Oasis Valley. The electrically conductive nature of this fault zone indicates the presence of abundant alteration minerals or a dense network of open and interconnected fractures filled with electrically conductive groundwater. The formation of alteration minerals require the presence of water suggesting that an extensive interconnected fracture system exists or existed at one time. Thus, the fractures within the fault zone may be either a barrier or a conduit for groundwater flow, depending on the degree of alteration and the volume of open pore space.

In Oasis Valley basin, a conductive surface layer, composed of alluvium and possibly altered volcanic rocks, extends to a depth of 300 to 500 m. The underlying volcanic layer, composed mostly of tuffs, fills the basin with about 3-3.5 km of relief on basement. A fault zone, related to the southern margin of the basin, appears to extend up to a depth of about 500 m. The path of groundwater encountering this fault zone is uncertain but may be either to the southwest towards Beatty or to the south towards Crater Flat.

The Report in PDF Format

This report is provided here as a PDF file. It consists of 39 pages including 16 figures and two tables. Many of the illustrations are in color and are provided at high enough resolution that you can get high-quality copies on your printer.

To view PDF publications on this Web server, you will need Adobe Acrobat Reader.

Magnetotelluric Study of the Pahute Mesa and Oasis Valley Regions, Nye County, Nevada (1.1 MB)

Click the link above to view the report.

View the version history

CLICK HERE view the version-history file for this report.
To contact the senior author, email Cliff Schenkel (schenkel@mojave.wr.usgs.gov).

The URL of this page is http://geopubs.wr.usgs.gov/open-file/of99-355/index.html
Date created: 11/23/1999
Last modified: 11/30/1999
Email technical-support comments to Mike Diggles (mdiggles@mojave.wr.usgs.gov).