Cryptic Faulting and Multi-Scale Geothermal Fluid Connections in the Dixie Valley-Central Nevada Seismic Belt Area; Implications from MT Resistivity Surveying

Abstract

Extended magnetotelluric (MT) profiling results over the Dixie Valley-Central Nevada Seismic Belt area were recently completed to explore the hypothesis that fluid circulation to depths of 10 km or more is generating well temperatures in the field >280 C. This transect has revealed families of resistivity structures commonly dominated by high-angle features, some of which may be of key geothermal significance. Most notably, 2-D inversion of these data has resolved a high-angle, conductive fault zone-like structure extending from the base of Dixie Valley to a broad, deep crustal conductor beneath the Stillwater-Humboldt Range area. The deep conductor is coincident with the Buena Vista anomalous seismic area and such conductors are generally correlated with magmatic underplating and fluid exsolution. This deeply extending, steep fault zone may be the means for deep transport of fluids upward to provide high temperatures at the Dixie Valley field, including a component of magmatic fluids consistent with recent He isotope studies and the existence of hot springs manifestations in the center of the valley. However, other important conductivity structures imaged in the transect include possible large-scale sedimentary folds in the Phanerozoic continental shelf section, and overthrusting near the margin with the Sierra Nevada plutonic province. West of San Emidio hot springs, we appear to encounter relatively rigid, resistive Sierran basement. This experience highlights the need to bring external constraints when interpreting resistivity in the Great Basin. Apart from possible deep vestiges of Mesozoic or younger batholithic volumes, the lower electrical crust at least in this region of the Great Basin is primarily a modern feature.