VERTICAL AXIS CLOCKWISE ROTATION OF FAULT BLOCKS IN THE EASTERN MONO BASIN, CALIFORNIA AND NEVADA

The Adobe Hills in the eastern Mono Basin, California, are located between two regions with dramatically different mechanisms for transferring slip between subparallel strike-slip faults and connecting faults. The geometry and orientation of the prominent sinistral faults in the area are consistent with previous data for simple shear coupled with clockwise block rotation. This multi-faceted study hypothesizes that early Miocene deformation was located in eastern California near the Sierra Mountain Front prior to stepping east into the Mina Deflection during the late Miocene to early Pliocene. This research uses paleomagnetic techniques to analyze vertical-axis rotation between structural blocks by comparing the angular dispersion of the study sites to the paleomagnetic reference pole. All sampling sites are located in stratigraphically continuous basalt flow sections located on separate structural blocks to evaluate the magnitude of vertical axis rotation with respect to the late Miocene to early Pliocene time averaged field direction. Petrographic analyses reveal that the basalts are primarily composed of a plagioclase matrix with concentrically zoned augite phenocrysts, and small, cubic, opaque crystals typical of maghemite that are conducive for providing paleomagnetic data. Meso-scale interpretations of structural data and the identification of basalt flows to determine sampling locations were performed using Landsat 8 imagery and a 752 band combination. The basalts from the Adobe Hills have yielded a stable single component magnetization that decays fairly linear to the origin during alternating field demagnetization, although some sites yield a more complex demagnetization behavior involving magnetization components that require a combination of alternating field and thermal demagnetization to isolate the characteristic remanent magnetization. Thirty-four sites from the Adobe Hills basalts have indicated clockwise vertical axis rotation ranging from +15° ± 10° to +50° ± 10° in areas that occur outside what was previously thought to be unrotated. This study provides the first paleomagnetic data for this area and will help form a better understanding of the processes involved with the transfer of slip and extend the areas of impact for future studies concerning slip transfer systems.