QUATERNARY SLIP HISTORY OF THE SOUTHERNMOST WHITE MOUNTAINS FAULT ZONE, OWENS VALLEY, CALIFORNIA

The NNW-striking Eastern California Shear Zone (ECSZ) is a ~50–100-km-wide corridor of intracontinental right-slip shear that accommodates up to ~25% (~10–13 mm/yr) of relative North American-Pacific plate motion (~50 mm/yr). The northern ECSZ is ~300 km long and bounded by the White Mountains fault zone (WMFZ) and Owens Valley fault to the west. Quaternary right slip along the WMFZ accounts for ~3–12% (0.4–1.4 mm/yr) of the ECSZ slip budget. In addition, the WMFZ accommodated E-W-oriented crustal extension in Owens Valley since the Miocene. Several studies have constrained the Quaternary extensional and right-slip histories of the northern and central WMFZ. In contrast, little is known regarding the recent slip history of the southernmost WMFZ in central Owens Valley, where right slip may be partly transferred to from the Owens Valley fault (2.8–4.5 mm/yr) in the south. To address this question, we conducted Quaternary geologic mapping, surveying, and luminescence dating of the southernmost WMFZ, located directly north of CA State Route 168. There, the fault zone is expressed as a 1.5–2 km-wide area of mostly west-facing normal fault scarps and right-laterally offset drainages in range-front alluvial fans. Few left-laterally offset drainages also occur in the area. Preserved normal and strike-slip fault surfaces have an average strike of 345° and dip of 75°W. Extensional and right-slip displacements of alluvial fans inferred to be ca. 78 ka are 11–13 m and ~16 m, respectively. These displacements yield respective extensional and right-slip rates of 0.14–0.17 mm/yr and ~0.21 mm/yr since the latest Pleistocene. Extensional and right-slip displacements of older fans inferred to be ca. 760 ka are 22–35 m and ~180 m, respectively. These displacements yield respective extensional and right-slip rates of 0.03–0.05 mm/yr and ~0.24 mm/yr since the middle Pleistocene. Our rates suggest that northward slip transfer from the Owens Valley fault is partitioned to multiple faults rather than only the WMFZ, which is consistent with previous models. Our results also show that extension across central Owens Valley since the late Pleistocene has been slower compared to that in the north.