QUATERNARY DEXTRAL FAULT SLIP HISTORY ALONG THE WHITE MOUNTAINS FAULT ZONE, CALIFORNIA

Geologic and geodetic studies show that dextral shear within the Eastern California Shear Zone (ECSZ) accounts for 20-25% of the relative motion between the Pacific and North Americas plates. A significant component of this dextral shear is accommodated along the Owens Valley-White Mountains fault system. A recently published kinematic model for the ECSZ suggests that since ~1.7 Ma, 15-40% of Owens Valley fault slip was captured by the Deep Springs normal fault and transferred eastward to the Fish Lake Valley fault zone. Based on this model, 1.0-2.8 mm/yr of Owens Valley fault slip continues northward along the White Mountains fault zone (WMFZ) (Lee et al., 2001). New geologic mapping, geomorphic, and geochronologic investigations along the WMFZ shed light on its Quaternary dextral fault slip history and allow us to test this kinematic model. The WMFZ is composed of a network of NNW-striking right lateral strike-slip faults and NNE-striking, primarily W-dipping normal faults that bound the western side of the White Mountains. This fault zone cuts Quaternary coarse- to fine-grain alluvial fan deposits interbedded with tuffaceous sand, partially welded tuff, and Bishop ash. Based on alluvial fan surface morphology, such as terrace height, presence or absence of bar and swale morphology, degree of fan dissection, and degree of desert pavement development, we have identified three Quaternary alluvial fan surfaces of distinct ages. Tectonic geomorphic features such as linear fault scarps, closed depressions, ponded alluvium, offset alluvial fans, deflected drainages, and shutter ridges indicate that dextral faults cut these alluvial surfaces. Drainages and shutter ridges show offsets that range from 5 to 370 meters. 10Be cosmogenic radionuclide (CRN) dating methods used on in situ boulders demonstrate that the age of the oldest fan surface is ~200 ka. Maximum offset of this oldest fan surface is ~370 m, yielding a late Pleistocene slip rate of ~1.8 mm/yr. Therefore, the slip rate estimate determined in this study is consistent with the model proposed for the WMFZ.