New geologic map: Emerson Pass geothermal area, Washoe County

Open-File Report 13-10 (second edition)

Preliminary geologic map of the central Lake Range, southern Fox Range, and northern Terraced Hills, Emerson Pass geothermal area, Washoe County, Nevada, by Ryan B. Anderson, James E. Faulds, and Gregory M. Dering, 2014

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Detailed geologic mapping and stratigraphic-structural analyses have elucidated the kinematics, stress state, and structural controls of a “blind” geothermal system in Emerson Pass on the Pyramid Lake Paiute Tribe Reservation, western Nevada. The Emerson Pass area resides near the boundary of the Basin and Range and Walker Lane provinces of northwestern Nevada, at the northeast end of Pyramid Lake. Strata of the surrounding Fox Range, Lake Range, and Terraced Hills are comprised of late Miocene to Pliocene sedimentary rocks and the middle Miocene Pyramid sequence volcanic rocks, all overlying Cretaceous intrusions and Triassic to Jurassic metasedimentary rocks.

The active geothermal system is expressed as a 2-m shallow temperature thermal anomaly (maximum ∼60°C) that lies at the western edge of a broad left step at the northeast end of Pyramid Lake between the north- to north-northeast-striking, west-dipping, Fox and Lake Range normal faults. The 2-m temperature surveys have defined a north-south elongate thermal anomaly that resides on a north- to north-northeast-striking normal fault. Additionally, travertine mounds, chalcedonic silica veins, and silica-cemented Pleistocene lacustrine gravels in Emerson Pass indicate a robust geothermal system active at the surface in the recent past, likely the early Holocene. Structural complexity and spatial heterogeneities of the strain and stress field have developed in the step-over region, but kinematic data suggest a west-northwest-trending (∼280° azimuth) extension direction. The geothermal system is likely hosted in Emerson Pass as a result of enhanced permeability generated by the intersection of two oppositely dipping, southward- terminating north- to north-northwest-striking (Fox Range fault) and north-northeast-striking normal faults.

This publication was prepared with support from the U.S. Department of Energy. We thank the Pyramid Lake Paiute Reservation for access to tribal lands and logistical support throughout the project.

Geochronologic data (several 40Ar/39Ar dates) were added to this second edition.

Open-File Report 13-10 (second edition, 2014) supersedes the first edition (2013).

Open-File Report 13-10 (second edition), one color plate with 3 cross sections, 51.5 x 39.5 inches, scale 1:24,000; inset map, scale 1:8,000; 10-page text, b/w, $22.00 for paper copy—or free on the Web:
http://www.nbmg.unr.edu/sales/pbsdtls.php?sku=OF13-10

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