LATE CENOZOIC EXHUMATION OF THE AVAWATZ MOUNTAINS, CALIFORNIA: IMPLICATIONS FOR THE INITIATION OF THE GARLOCK FAULT

The tectonic role of the left-slip NE-striking Garlock fault in accommodating NW-trending Pacific-North American relative plate motion remains unresolved. An improved understanding of how slip is accommodated along strike, specifically near the eastern end, can help us better understand the kinematic evolution of the Garlock fault. The Avawatz Mountains are located at the eastern tip of the Garlock fault where it intersects the NW-striking Southern Death Valley fault system (SDVF). The Avawatz Mountains were constructed via late Cenozoic contractional deformation involving active thrust and/or oblique-slip faults. This zone may represent a termination thrust belt of the Garlock fault or a restraining bend along the SDVF. Here we present new detailed geologic mapping, structural analysis, and low-temperature thermochronology to resolve the timing and kinematics of deformation as it relates to either fault system. Field observations show numerous strike-slip faults in the western portion of the range, and west-dipping reverse faults along the eastern range front. New and compiled zircon and apatite (U-Th)/He and apatite fission track thermochronology from a ~1km vertical transect in the hanging wall of the eastern range-front fault suggest late Miocene exhumation and thrust-fault initiation. Apparent west-east shortening rates across the Avawatz Mountains are comparable to slip rates along the eastern Garlock fault. Taken together, our observations suggest a complex fault and exhumation history that may reflect transfer of strike-slip displacement onto a termination thrust system that was later overprinted as a restraining bend in the SDVF. We interpret this deformational history to be most consistent with rotating-fault models for the Garlock fault, where a broad plate-boundary dextral shear zone leads to clockwise rotation of and left-slip displacement along the Garlock fault. Strike-slip displacement is observed to decrease towards the ends of the Garlock fault, where it is transferred to termination structures. Continued shear along the plate-boundary leads to the development of shear-zone parallel structures (SDVF) that complexly overprint the eastern tip of the Garlock fault.