Resolving space-time strain paths of the Panamint and Cottonwood Mountains, eastern California, through bedrock thermochronology and detrital geochronology
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The landscape in Death Valley region is the result of a complex history that includes Miocene Basin and Range extension and Miocene to recent transtension. Despite being one of the best studied regions in the world, reconstructing the displacement histories of fault-bounded ranges has been a challenge due to difficulty in identifying reliable strain markers and timing constraints. Many of the palinspastic reconstructions produced rely on the strain markers much older than Cenozoic extensional and transtensional faults, and whose restored positions are not well-resolved. Here we present new (U-Th)/He thermochronology data from the Panamint Range and Cottonwood Mountains, west of Death Valley. The data are used to evaluate the timing, magnitude, and spatial pattern of strain associated with the faults in these ranges. We also present new detrital zircon U-Pb data from the Nova basin, in the northern Panamint, which provide additional constraints on the timing of fault motion. The new thermochronology data comes from 36 samples collected from transects and sites in the ranges. In the northern part of the Panamint Range, apatite He (AHe) ages from a transect across the Skidoo pluton, in the footwall of the Panamint-Emigrant detachment (PED), show continuous exhumation from [approximately] 8-4 Ma. Zircon He (ZHe) data from the same transect preserve a zircon He partial retention zone (PRZ). In the southern part of the range, AHe ages from Goler Canyon record rapid exhumation at 4 Ma and an AHe PRZ. ZHe data from this transect also record cooling between 80-50 Ma, similar to AHe and ZHe ages from a transect in the Cottonwood Mountains. Paleodepth reconstructions of samples from the Panamint Range suggest that the northern part of the range experienced 4.2-7.2 of vertical exhumation, compared to only 1.9-2.4 km of exhumation in the southern part of the range. This difference in magnitudes is also reflected in the fault timing data, which indicate that middle to late Miocene exhumation was concentrated in the northern part of the range. Although both parts of the range see [approximately] 4 Ma exhumation, apatite ages from two key sites, near the intersections of the Manly Pass and Hunter Mountain faults with the PED, record younger cooling at 2.8-2.6 Ma. These latest Pliocene ages are similar to AHe ages from the Inyo Mountains (2.8 [plus-minus] 0.7 Ma; Lee et al., 2009) that have been interpreted as reflecting the timing of initiation of the Hunter Mountain fault. Together, the new and the published data show a complex history, with multiple episodes of deformation, beginning in the Late Cretaceous and continuing through the latest Pliocene. The data also suggest that the transition from the Basin and Range extension to the dextral transtension may have initiated at [approximately] 4 Ma, but the full integration of this system of faults may not have occurred until the latest Pliocene.
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