TIMING OF INTERCONTINENTAL DEFORMATION ACROSS 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 dextral, changing to, sinistral transfer faults in the area are consistent with previous data for simple shear coupled with clockwise block rotation. This multi-faceted study hypothesizes that Miocene deformation extended west into California to the Sierra Mountain Front prior to stepping east into the Mina Deflection in the late Miocene. The research primarily focuses on stacked basalt sequences and paleomagnetic techniques to analyze vertical-axis rotation by comparing the directional data from study sites to established paleomagnetic poles of late Miocene age. Petrological analyses of thin-sections determined that the basalts are primarily composed of a plagioclase matrix with large concentrically zoned augite clasts, and small, cubic, opaque crystals typical of a Fe-oxide phase. Interpretations of structural data and the identification of basalt flows were used to determine coring locations using a 752 band combination from Landsat 8 imagery. To limit the timing of fault block rotation, Ar40/Ar39 dating of sanidine, biotite, and hornblende phenocryst separates from flow and tuff samples are under way and should help constrain the temporal evolution of extrusive magmatism. The preliminary results from paleomagnetic analyses show that varying degrees of vertical-axis rotation across fault bounded structural blocks were found in areas that occur outside of what was previously thought to be an undeformed zone. Additional field work and laboratory analyses are in progress and will build upon data collected thus far. This study is providing the first paleomagnetic data for the area and will help form a better understanding of the processes involved with displacement and extend areas impacted by deformation.