EFFECTS OF CHANGING FAULT KINEMATICS ALONG THE OWENS VALLEY FAULT ZONE ON THE TECTONIC EVOLUTION OF THE OWENS VALLEY BASIN, EASTERN CALIFORNIA SHEAR ZONE

The dextral oblique Owens Valley Fault (OVF) is a key component of the Eastern California Shear Zone (ECSZ) currently accommodating transtensional motion between the northwest-moving Sierra Nevada microplate and stable North America. Although the Late Pliocene to Recent extensional evolution of the Owens Valley basin is geomorphically well displayed, the role of the OVF in its tectonic formation and the temporal effects of strike-slip tectonics on basement geometry have not been well constrained. The source of bedrock units exposed at the Pleistocene-age Poverty Hills transpressional uplift has significant implications for the amount/evolution of strike-slip motion on the Owens Valley Fault.

The Owens Valley basement is a composite of smaller bedrock blocks that have subsided differentially between the bounding ranges during the last ~3 m.y. A 3-dimensional model of northwest-directed transtension distributed across the OVF and the rangefront faults is proposed herein to explain the observed basement geometry. The apparent lack of field evidence for strike slip motion on the OVF has led to purely extensional, Basin and Range-style models of Owens Valley basin development. Inclusion of horizontal displacement during the rapid vertical separation of the Owens Valley/White-Inyo Mtns. demonstrates the spatial and temporal formation of discrete sub-grabens in the northern and southern Owens Valley and a shallow bedrock anomaly dividing them.

Concurrent local transpressional uplift and transtensional volcanism occurring within the last ~1 m.y. along the OVF suggest a change in local fault kinematics that may have resulted in a change in fault geometry. We propose that the OVF may have stepped westward from its continuation with the White Mountain Fault to its present location beneath Crater Mountain during the early- to mid-Pleistocene, in response to rapidly evolving transtensional fault patterns. This proposed change in geometry further resolves differential subsidence of the Owens Valley basin and fits well within the developing regional transtensional fault pattern of the ECSZ. This time period also corresponds with intense mid- to late-Pleistocene vertical and horizontal tectonism, and the migration of overall slip transfer through Deep Springs Valley into the Fish Lake Valley Fault to the east.