GEOLOGIC MAPPING OF THE LA PLATA CANYON AREA, CHURCHILL COUNTY, NEVADA

This study examines a perched Neogene lacustrine basin sequence at the southern end of the Stillwater Range, near La Plata Canyon in Churchill County, Nevada and provides new insight on the local onset and style of deformation. The La Plata Canyon area contains active Basin and Range normal and oblique slip faulting and intermittent strike-slip faulting due to a potential accommodation of elevated horizontal stresses from motion in the adjacent Walker Lane. The study area also resides in an accommodation zone that forms a stepover from the Sand Springs Range frontal fault to the Stillwater Range frontal fault. The Elevenmile Canyon geothermal system, a fault-controlled, low temperature, blind geothermal system, also resides in the accommodation zone.

Neogene basin deposition, burial, exhumation, and deformation onset were examined through the construction of a detailed digital geologic map, completed at a scale of 1: 24,000. The characterization of the structural framework within the Neogene basin sequence and the younger units was completed by examining fault kinematics and geometries and then conducting stress inversions for comparison of paleostress to modern stress. Ar-Ar geochemistry samples were also collected and analyzed in the volcanic sequence to further refine the estimates of timing. The mapping area also includes partial aeromagnetic and gravity survey data, as well as partial LiDAR.

The basin sequence unconformably overlies steeply tilted units of the Oligocene-Miocene Stillwater Caldera Complex and conformably underlies the 14-16 Ma volcanic sequence of basalt and basaltic andesite flows. The basin sequence and the overlying volcanic sequence were deformed in the same period of early Basin and Range extension following the end of deposition of the volcanic sequence at around 14.34 Ma (The stratigraphically youngest age). Stress Inversions demonstrate that early Basin and Range extension (279°) that affected the basin sequence underwent a minor (10-15°) clockwise rotation of the minimum horizontal stress to achieve the modern stress (296°), a likely result of increased dextral shear in the Walker Lane. This study resolves a brief sequence of geologic events for the La Plata Canyon area leading up to initiation of Basin and Range extension and formation of the Walker Lane.