Possible Magmatic Input to the Dixie Valley Geothermal Field, and Implications for District-Scale Resource Exploration, Inferred from Magnetotelluric (MT) Resistivity Surveying

Abstract

Magnetotelluric (MT) profiling in northwestern Nevada is used to test hypotheses on the main sources of heat and hydrothermal fluid for the Dixie Valley-Central Nevada Seismic Belt area. The transect reveals families of resistivity structures commonly dominated by steeply-dipping 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. Decomposed impedance axis analysis suggests the overall trend of this break is nearly N-S. 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. This experience highlights the need to bring external constraints when interpreting resistivity in the Great Basin.