INTEGRATION OF THE SEARLES VALLEY, PANAMINT VALLEY, AND HUNTER MOUNTAIN FAULTS FROM LOW-TEMPERATURE THERMOCHRONOLOGY

The Panamint Valley region is host to a complex system of normal and strike-slip faults that transfer strain from the Searles Valley to the Panamint Valley via the Manly Pass fault, and from the Panamint Valley to Saline Valley via the Hunter Mountain fault. Although this system of faults appears to have been stable over that last 100,000 years, the timing of its establishment is not well known. Here we report new (U-Th)/He data from the Panamint Range and Cottonwood Mountains that shed light on the development of this coordinated system of structures. The new data were obtained 38 samples collected from three transects and two key sites in these ranges. Apatite He ages from a transect across the Skidoo pluton, in the footwall of the Panamint-Emigrant detachment (PED) in the northern part of the range, record continuous exhumation from ~8-4 Ma. In the southern part of the range, apatite ages from Goler Canyon preserve rapid exhumation at 4 Ma and a structurally higher partial retention zone. Although the ~4 Ma timing from these transects is consistent with published ages from the central Panamint Range and northern Slate Range, apatite He ages from two key sites, near the intersections of the Manly Pass and Hunter Mountain faults with the PED, record cooling at 2.8-2.6 Ma. These latest Pliocene ages are similar to apatite He ages from the Inyo Mountains (2.8 ± 0.7 Ma; Lee et al., 2009), inferred to record renewed slip along the eastern Inyo fault zone and the initiation of the Hunter Mountain fault. Taken together, the new and previously published data indicate that the transition from Basin and Range extension to dextral transtension may have initiated at ~4 Ma, but full integration of this system of faults may not have occurred until the latest Pliocene.