SLIP HISTORY MODEL OF THE GARLOCK FAULT ZONE: BASIN AND RANGE EXTENSION OVERPRINTED BY EASTERN CALIFORNIA SHEAR ZONE TRANSTENSION

We present an animated Late Cenozoic slip history model of the Garlock fault within a regional context based on new mapping and geochronologic data covering the central segment of the Garlock fault. Our study concentrated on the intersections of the Garlock fault with NNW-trending dextral faults. We examined four of these intersections: Blackwater, Sierra Nevada Frontal, Cerro Coso, and Southern Panamint Valley faults. These intersections are important in that dextral shear dominates the central Garlock fault region but dextral faults do not cut the Garlock fault. We did a detailed analysis of the Lava Mountains-Summit Range (LMSR) where the dextral Blackwater fault meets the Garlock fault. The LMSR contains a crucial record of deformation with Early, Middle and Late Miocene volcanism. Our observations led to new kinematic, geochronologic and rock unit correlation data.

We combined our new data with deformation constraints from other studies in the Mojave Desert and western central Basin and Range (WCBR) to create a fault-slip model of the central and eastern Garlock fault. Our model is a two-stage deformation history of the Garlock fault, based on our observations from the LMSR and relationships across the region. We compiled geologic and kinematic data for the WCBR and Mojave Desert along the central and eastern Garlock fault into a GIS database. From this we created a series of time slices to animate the slip history of this region.

The earlier phase of deformation is synchronous with rapid exhumation in the WCBR starting at ~11 Ma. This Garlock fault displacement occurs during a westward-propagating wave of the extension in the WCBR but not in the Mojave Desert. A second phase of slip on the Garlock fault occurs during dextral transtension during the Eastern California Shear Zone. The extension in the WCBR during transtension also occurs as a westward propagating wave of deformation. We interpret the left-lateral slip on the Garlock fault during the Late Miocene to Holocene to be a response to dextral transtension of the ECSZ. The Garlock fault appears to be a preferential reactivation of a weak lithospheric shear zone. The results of our model show that the central Garlock fault is a complex, narrow to 20 km wide fault zone with the majority of slip on the Garlock fault zone occurring during the Late Miocene and younger deformation.