IMPLICATIONS OF DETRITAL ZIRCON U-PB GEOCHRONOLOGY AND BEDROCK THERMOCHRONOLOGY IN THE AVAWATZ MOUNTAINS FOR THE EXTENT AND DEFORMATION HISTORY OF THE SOUTHERN DEATH VALLEY FAULT

The Garlock fault zone is a sinistral structure within SE California related to the San Andreas fault zone, spanning 240 km until it meets the dextral southern Death Valley fault zone, which makes up part of the Eastern California shear zone. At this intersection, the Garlock fault zone gains a thrust component and uplifts the Avawatz Mountains. The timing and interactions of these faults and extent of the southern Death Valley fault zone past this intersection are poorly understood. This study uses zircon (U-Th)/He dating, thermal history modelling, and U-Pb detrital zircon provenance analysis to explore 1) the exhumation history of the Avawatz Mountains and 2) the extent of the southern Death Valley fault zone. Six zircon (U-Th)/He ages were determined for the northern Avawatz Mountains. Zircon (U-Th)/He mean ages vary from 6.3 ± 1.4 Ma to 74.0 ± 10.7 Ma (2σ). Ages do not appear to correlate to grain mass, [U]e, or elevation and are likely a function of exhumation by faults alone. The results document cooling during the Late Cretaceous (~71-75 Ma), Paleogene (~30-45 Ma), and Miocene (~6.3 Ma). Time-temperature history models of these ages and existing data constrain the timing of Cretaceous—Miocene exhumation. U-Pb detrital zircon provenance analysis was also conducted to constrain the extent of the southern Death Valley fault zone. A previous study proposed that the Miocene Military Canyon Formation in the Avawatz Mountains is sourced from the Halloran Hills, which are now 20 km to the south, and they have since been offset by the southern Death Valley fault. Conglomerate samples from the Military Canyon Formation and the coeval Shadow Valley Basin Member II in the Halloran Hills were analyzed to test this hypothesis. U-Pb detrital zircon ages are dominantly Jurassic and Precambrian (~1800-1500 Ma) in the Military Canyon Formation, consistent with proximal sources, while the Halloran Hills sample shows a dominant age peak at ~90 Ma and is likely sourced from the Teutonia batholith. These data show that the formations are not related and cannot serve as strain markers for the southern Death Valley fault. The arrangement of thermochronology ages and lack of evidence for Miocene offset also suggest that the southern Death Valley fault may have been a normal fault at this time, similar to the nearby Arrastre Spring and Amargosa faults.