Strike-slip fault system in Amargosa Valley and Yucca Mountain, Nevada

Abstract

The Amargosa Desert fault system, part of a 250-km-long system of dextral strike-slip faults east of the Death Valley region, is a throughgoing, long-lived, NW-striking, dextral strike-slip shear system that lies beneath Crater Flat and Yucca Mountain. Evidence for the fault system includes gravity, seismic, structural, stratigraphic, and paleomagnetic data, the distribution of springs and basaltic volcanic centers, and patterns of late Quaternary surface faulting. Where the Amargosa Desert fault system passes beneath Miocene ash-flow tuffs of the Southwestern Nevada Volcanic Field, we infer that the fault system changes into a series of detachments near the basement/cover contact and is expressed as a system of rotational normal faults in the ash-flow tuffs. Displaced geologic features indicate that total dextral displacement on the Amargosa Desert fault system exceeds 30 km. Vertical-axis rotations in ash-flow tuffs suggest that about 25 km of dextral displacement may have occurred since about 12.75 Ma. This fault system has important implications for the proposed high-level nuclear waste repository at Yucca Mountain, since it has experienced Quaternary and possibly Holocene displacements. Both normal faults and basaltic volcanic cones near the proposed repository may be controlled by the evolution of this regional strike-slip fault system.