TESTING KINEMATIC MODELS IN THE EASTERN CALIFORNIA SHEAR ZONE – WALKER LANE BELT: FIELD STUDIES IN THE SOUTHWESTERN MINA DEFLECTION, CALIFORNIA – NEVADA

The Mina deflection (MD) is a ~125 km long structural step-over within the NW-striking dextral Eastern California Shear Zone (ECSZ) – Walker Lane Belt (WLB). Fault slip transfer within this step-over, from the NW-striking dextral faults in the northern ECSZ to the NW-striking dextral faults in the central WLB, is accommodated by a combination of sinistral, dextral, and normal faults. New geologic mapping, structural, kinematic, and geochronology studies in the River Spring area (RSA) of the southwestern MD provide insight into the kinematics of fault-slip transfer from the ECSZ to the MD. The RSA is a faulted volcanic field underlain by Miocene andesite (~20 to 14.4 ± 0.8 Ma), dacite (14.4 ± 0.8 Ma), latite tuff (11.17 ± 0.04 Ma), Pliocene tuffaceous sandstone, basalt flows (3.41 ± 0.02 Ma to 3.47 ± 0.01 Ma), andesite, and cinder cones (2.94 ± 0.06 Ma), and Quaternary alluvium, playa, and eolian deposits. Faults, which cut all but the Quaternary units, define three zones based on fault type and strike: (a) NW-striking dextral faults in the south, (b) NE-striking sinistral faults in the north, and (c) the western termination of the EW-striking sinistral Coaldale fault in the center. The NW-dextral and NE-EW-sinistral faults are mutually cross-cutting, illustrating the complex fault interactions that result in fault slip transfer from the dextral faults of the ECSZ to the sinistral faults of the MD. Offset markers identified along the strike-slip faults include basalt ridge lines, faults, and unit contacts and yield a minimum dextral offset of 1232 ± 203 to 1308 ± 327 m and sinistral offset of 420 ± 153 m. Combining magnitude of offset measurements with age of offset units yields net minimum dextral and sinistral slip rates of 0.4 ± 0.1 mm/yr and ~0.1 mm/yr, respectively. By comparing fault zone geomorphology, we estimated fault slip rates on fault zones for which offset markers were not observed. Based on this analysis, our preferred net minimum dextral and sinistral fault slip rates across the RSA are 0.5-0.7 mm/yr and 0.3-0.4 mm/yr, respectively. Our calculated fault slip rates for the RSA are less than slip rates predicted in the kinematic models of Nagorsen-Rinke et al. (2013) and Lee et al (2009b), suggesting significant offset along faults for which we do not have offset measurements.