HETEROGENEOUS EXTENSION ALONG THE NORTHERN BOUNDARY OF THE CENTRAL BASIN AND RANGE SUB-PROVINCE: THE KANE SPRINGS WASH FAULT, SOUTHERN NEVADA

The boundary zone between the northern (NBR) and central (CBR) Basin & Range sub-provinces exposes Miocene to Quaternary (Q) strike-slip and normal faults. Defining the role of the major, NE-striking strike-slip faults is important because of their location (1) along the tectonic boundary and (2) within a zone of modern seismicity – the southern Nevada seismic belt. One such strike-slip fault is the Kane Springs Wash fault zone (KSWF). The NE-striking KSWF lies in SE Nevada, ~120 km N of Las Vegas. The KSWF is a 41 km long left-lateral fault zone with 8-12 km of strike slip based on the offset of a ~15 Ma caldera wall. Our objective is to determine fault geometries and kinematics, and the role of the KSWF in a regional context. New data include 1:12K scale geologic maps and fault scarp profiles collected using a total station.

We document a negative flower structure using fault scarp height measurements and show different bedrock fault numbers, strikes, and total extension on either side of the KSWF based on map data. Within the Q units, the KSWF contains NE-striking normal-left, left-stepping faults, with a releasing stepover that forms the negative flower structure. Scarp profiles record up to three faulting events; larger scarps range from 8 to 13 m high. Scarps formed in any one event average ~3 m. Scarp heights along strike show a minimum near the negative flower structure, suggesting that two fault segments linked or are linking. No Q scarps abut the KSWF. The faults exposed only in bedrock differ on either side of the KSWF. NW of the KSWF, (1) numerous major faults strike ~NNE, (2) faults abut the KSWF as expected for strain transfer, and (3) small cross faults between major faults. They lack Q fault scarps, but offset a ~15 Ma tuff. In contrast, SE of the KSWF the abutting faults strike NE, are less abundant and lack cross faults. The southern faults have down-to-the-NW displacement. One southern fault continues from bedrock exposures into Q scarps. These observations suggest that: (1) between 15 Ma and early Q the KSWF was a transfer fault zone that accommodated differences in extension on either side; (2) the KSWF linked in the Q without faults that transfer slip onto it. Thus, the KSWF is a Miocene transfer fault with a distinct Q history suggesting that deformation within the NBR-CBR boundary has changed through time.