STRUCTURAL DEVELOPMENT AND TECTONIC ROLE OF THE ARROWHEAD MINE FAULT, PAHRANAGAT SHEAR ZONE, NEVADA

The Basin and Range province is characterized by normal faults associated with extension, but the occurrence of strike-slip faults and the seismic hazard accompanying them is less understood. The Pahranagat shear zone (PSZ) ), in Lincoln County, Nevada, is a 20-25 km wide zone of Cenozoic left-lateral faults that lies within the boundary zone between northern Basin and Range (NBR) and central Basin and Range (CBR) sub-provinces. The NBR is characterized by greater levels of tectonic activity which is illustrated by geodetic data, earthquake locations, and by the fact that the NBR has higher heat flow than the CBR. The PSZ and the zone of recorded earthquakes that lies along it, the southern Nevada seismic belt, connects regional zones of active seismicity; it links the Intermountain Seismic Belt and the Eastern California Shear Zone/Walker Lane. The Arrowhead Mine Fault (AMF) is one of the three major faults in the PSZ and many normal faults terminate at this fault.

Geometric, spatial and kinematic analysis indicates kinematic compatibility between the normal faults and the AMF, suggesting that the AMF is a regional transfer zone, with kinematically linked normal faults along it. Strike-slip fault splays form a flower structure/duplex that formed synchronously with a number of normal faults in the area. Internally, the duplex contains both contractional and extensional structures. These relations were established through detailed mapping with emphasis on fault cross-cutting, termination, and kinematic relationships at 1:12,000 scale of the AMF in the East Pahranagat Range. Additionally, stereographic analysis of bedding and compaction foliation data along with cross sections and a fence diagram provides further evidence that the AMF is a transfer fault. Fault cross-cutting relationships indicate that the AMF cuts Kane Wash Tuff, Gregerson Basin Member, along the eastern strand, constraining the age to 14 Ma or younger. By constraining the age and style of deformation of the AMF we find that the PSZ was active late in the development of the NBR to CBR boundary zone.