GEOLOGIC INVESTIGATIONS IN THE BLACK MOUNTAIN AREA, NORTHERN EASTERN CALIFORNIA SHEAR ZONE: TESTING A KINEMATIC AND GEOMETRIC FAULT SLIP TRANSFER MODEL

New geologic mapping, structural, and Ar/Ar geochronology studies in the Black Mountain area (BMA), northern eastern California shear zone (ECSZ), are used to test a kinematic fault slip transfer model for the Owens Valley fault (OVF)-Mina deflection (MD) transition and to help resolve the discrepancy between geologic slip rates and geodetic strain rates across this region. The BMA exposes Mesozoic igneous basement nonconformably overlain by Miocene rhyolite tuffs (~22.4 Ma) and andesite lava flows, Miocene to Pliocene sedimentary deposits, Pliocene (~3.53 to ~3.29 Ma) basalt flows, and Quaternary (~1936 to ~766 ka) rhyolite tuffs and sedimentary deposits. Angular unconformities characterize the contacts between Miocene, Pliocene, and Quaternary units, suggesting a Miocene and a Pliocene-Quaternary deformation episode. Range bounding ~NS- to NNW-striking, west-dipping normal faults and secondary ~NW- to NE-striking, west-dipping normal faults cut all units, except most middle Pleistocene to Holocene sedimentary deposits. Areally extensive Pliocene basalt flows emplaced upon a subhorizontal surface provide an ideal marker for documenting fault offset and tilts. These basalts are tilted ~20-30° and exhibit 10-1330 meters of throw across normal faults. Palinspastically restoring offset Pliocene basalt flows in cross-sections yields horizontal extension magnitudes of 1.1 ± 0.5 km (11%) to 1.5 +0.7/-0.6 km (20%) across the BMA since basalt emplacement ended at ~3.29 Ma. Combining extension magnitudes with basalt ages yields a preferred ~ENE-WSW extension rate of ≥0.5 ± 0.2 mm/yr since ~3.29 Ma. We combine our new extension rate with slip rates on nearby fault zones to refine a kinematic fault slip transfer model for the OVF-MD transition, whereby ≥2.8 mm/yr of dextral slip on the OVF is partitioned northeastward onto the White Mountains fault zone and northward onto the Volcanic Tableland-Black Mountain-River Spring fault zone and into the Adobe Hills area of the southwestern MD. At least 0.6 mm/yr of dextral slip on the OVF remains unaccounted for in this kinematic model. Our new fault slip rates, combined with published fault slip rates, reduce, but do not solve, the discrepancy between geodetic strain rates and geologic slip rates across the northern ECSZ.