Structural Controls of the Emerson Pass Geothermal System, Washoe County, Nevada
AuthorAnderson, Ryan Bruce
AdvisorFaulds, James E
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Detailed geologic 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 Mesozoic metasedimentary and intrusive rocks. A thermal anomaly was discovered in Emerson Pass by use of 2 m temperature surveys deployed within a structurally favorable setting and proximal to surface features indicative of geothermal activity. The anomaly 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 has a maximum recorded temperature of ~60°C and resides on a north- to north-northeast-striking normal fault. 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. 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. Therefore, geothermal activity will likely be hosted on north-to north-northeast striking normal faults. 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. The Lake and Fox Ranges contain a fault system that is organizing into a through-going fault by capture of a myriad of en echelon fault segments. This tectonic feature appears to provide a regional control on known geothermal systems, as systems are spatially associated with the lateral tips of fault segments that have been abandoned after hard linkage. On the basis of this observation, a number of geothermal exploration targets are generated in the region. The discovery and characterization of the Emerson Pass geothermal system may lead to unearthing of other hidden geothermal resources in the Basin and Range.