Structural Controls of the Tuscarora Geothermal Field, Elko County, Nevada

Abstract

Tuscarora is an amagmatic geothermal system located ~90 km northwest of Elko, Nevada, in the northern part of the Basin and Range province ~15 km southeast of the Snake River Plain. Detailed geologic mapping, structural analysis, and well data, have been integrated to identify the structural controls of the Tuscarora geothermal system. The structural framework of the geothermal field is defined by NNW- to NNE-striking normal faults that are approximately orthogonal to the present extension direction. Boiling springs, fumaroles, and siliceous sinter emanate from a single NNE-striking, west-dipping normal fault. Normal faults west of these hydrothermal features mostly dip steeply east, whereas normal faults east of the springs primarily dip west. Thus, the springs, fumaroles, and sinter straddle a zone of interaction between fault sets that dip toward each other, classified as a strike-parallel antithetic accommodation zone. Faults within the study area are mostly discontinuous along strike with offsets of tens to hundreds of meters, whereas the adjacent range-bounding fault systems of the Bull Run and Independence Mountains accommodate several kilometers of displacement. The geothermal field lies within a broad step over between the southward terminating Bull Run fault zone and the northward terminating Independence Mountains fault zone. Neither of these major fault zones is known to host high temperature geothermal systems. The northeastern Basin and Range currently hosts several known high temperature geothermal systems, which cumulatively produce <27 MW of electricity. Characterization of the structural controls at Tuscarora will benefit further development and exploration of geothermal resources in this tectonically distinct subprovince of the Basin and Range.