STRUCTURAL CONSTRAINTS OF BUFFALO VALLEY HOT SPRINGS AND PROXIMAL YOUNG VOLCANICS, NORTH CENTRAL NEVADA

The Humbolt Structural Zone (HSZ), located within a southwest-to-northeast band that stretches from west-central to north-eastern Nevada and Idaho, is noted for abundant high temperature (>100° C) geothermal systems. This is generally attributed to the unique structural setting formed by the transfer of tectonic stresses from the Walker Lane right-lateral strike-slip regime into Basin and Range extension. The resultant faults are both permeable and preferentially oriented for fluid flow in the northwest-directed extensional strain field. Increased heat gradient from extensional crustal thinning is the accepted source of calefaction for these systems and very few sites have demonstrated a magmatic heating component within the Basin and Range.

Buffalo Valley hot springs is a high temperature geothermal system located within the boundaries of the HSZ. Uniquely, this site is located proximal to a north-east-trending chain of morphologically young trachybasalt cones and flows that parallel the western Fish Creek Mountains range front. Although previously dated at 1.99-1.14 Ma using ⁴⁰Ar/³⁹Ar methods, the fresh morphology of the cones suggests that they are much younger. Preliminary geologic mapping has revealed a shear zone cutting through early Oligocene to Miocene tuffs and Quaternary basalt cones which are also oriented roughly parallel to the Fish Creek Mountains western range front. Additionally, several Quaternary scarps have been identified that offset fan deposits, basalt flows, and cinder deposits along similar strike.

The proximity and orientation of the newly discovered Fish Creek Mountains shear zone is consistent with the structural conduit necessary for extrusion of the Buffalo Valley cinder cones and flows. Likewise, outflow from this structure provides the most likely control for Buffalo Valley hot springs. A shared conduit could provide a unique scenario where a magmatic component to heating might be possible at this locality. Regardless, the presence of structurally constrained trachybasalts, late Quaternary scarps, and obvious fault permeability, suggest that the Fish Creek Mountains shear zone is a well-developed and locally dominant geologic structure.