Cosmogenic 10Be and 36Cl geochronology of offset alluvial fans along the northern Death Valley fault zone:: Implications for transient strain in the eastern California shear zone

[1] The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right-lateral strike-slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high-resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates similar to 297 +/- 9 m of right-lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic Be-10 and Cl-36 geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 + 22/-20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on Cl-36 depth profiles is 63 +/- 8 ka. Combining the offset measurement with the cosmogenic Be-10 date yields a geologic fault slip rate of 4.2 + 1.9/-1.1 mm yr(-1), whereas the Cl-36 data indicate 4.7 + 0.9/-0.6 mm yr(-1) of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of similar to 8.5 to 10 mm yr(-1). This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant.