TESTING RECONSTRUCTIONS OF MIOCENE TO PLIOCENE STRAIN IN THE PANAMINT VALLEY REGION WITH LOW-TEMPERATURE THERMOCHRONOLOGY

The Panamint Valley region has experienced a complex history that includes Miocene Basin and Range extension and Pliocene to recent dextral transtension. Although much is known about the tectonic development of this region, reconstructing the displacement histories of individual fault-bounded ranges has remained a challenge due to a lack of reliable strain markers and timing constraints. Here we report new apatite and zircon (U-Th)/He data from 37 samples collected from transects and sites in the Panamint Range and southern Cottonwood Mountains, which provide new constraints on the magnitude of Miocene-Pliocene strain in the region. Apatite He ages from the Skidoo pluton, in the footwall of the Panamint-Emigrant detachment (PED), in the northern Panamint Range record continuous exhumation from ~8 to 4 Ma. Zircon He ages from the same samples record rapid cooling at ~18 Ma and document an exhumed partial retention zone. By comparison, apatite He ages from Goler Canyon, in the southern part of the range, show rapid exhumation along the PED at ~4 Ma. Importantly, zircon He ages from these same samples lack evidence for Miocene exhumation and, instead, document a period of cooling from ~80-50 Ma, one that is also recorded by apatite and zircon He ages in the Cottonwood Mountains. Paleodepth restoration of our samples suggests that the northern Panamint Range experienced 4.2-7.2 km of vertical exhumation, compared to only 1.9-2.4 km of exhumation in the southern part of the range. Using the restored dip of the PED, the thermochronology data record 2.7 to 9.6 km of horizontal extension, substantially lower than what can be inferred from published palinspastic reconstructions. The discrepancy between the published models and our results may relate to a phase of Late Cretaceous to Eocene extensional exhumation that is unaccounted for in restorations that rely on pre-Cenozoic structures as strain markers.