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Abstract
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. One major strike-slip zone, the Pahranagat shear zone (PSZ), lies in Lincoln County, Nevada and within the boundary zone between northern Basin and Range (NBR) and central Basin and Range (CBR) sub-provinces. The PSZ is a 20- 25 km long zone of Cenozoic left-lateral faults. The Arrowhead Mine Fault (AMF) is one of the three major faults in the PSZ. The western AMF and the faults that surround and abut it are the foci of this research. The purpose of this research is to understand the timing and style of deformation of the AMF, the PSZ, and the relationship of the PSZ to regional tectonics. I hypothesize that the AMF is a recent tectonic feature that supports a model of regional sinistral transfer between tectonic regimes. The best way to obtain the spatial and geometric data needed to address the issue was detailed mapping with emphasis on fault cross-cutting, termination, and kinematic relationships at 1:12,000 scale of the western AMF and surrounding area in the East Pahranagat Range. New fault data, and stereographic analysis of bedding and compaction foliation data along with cross sections and a fence diagram provide evidence that the normal faults and strike-slip fault are kinematically compatible and were active synchronously, indicating that the AMF is a transfer fault. Strike-slip fault splays form a flower structure/duplex that are shown to have formed synchronously with a number of normal faults in the area. Internally, the duplex contains both contractional and extensional structures, divided by a through-going fault. This situation is uncommon in models of duplex formation, but is suggested here to have formed during segment linkage.
Cross-cutting relationships indicate that the AMF cuts Kane Wash Tuff, Gregerson Basin Member, along one strand, constraining the age to ∼15 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.
The PSZ plays a distinct role in the intraplate tectonics of the region, falling within the Southern Nevada Seismic Belt. It may be facilitating strain transfer from other sinistral structures within the Southern Nevada Seismic Belt (Caliente-Enterprise Zone, Rock Valley Fault Zone, etc.). The presence of both a western termination of the AMF and a gap in left-lateral structures to the west suggest that the NBR-CBR boundary is still developing, which has implications for the interconnectivity of Walker Lane with the Intermountain Seismic Belt and has implications for seismic hazard.
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