Constraints on exhumation and extensional faulting in southwestern Nevada and eastern California, USA, from zircon and apatite thermochronology

Eastern California and southwestern Nevada represent an area of Tertiary and Quaternary extensional and dextral transtensional deformation. We used zircon and apatite fission-track thermochronology to study the distribution and timing of tectonic exhumation resulting from extensional and transtensional detachment faulting in this area. Sampling efforts were focused on Paleozoic and Precambrian clastic sedimentary and metasedimentary rocks. Sixty-nine new apatite and zircon fission-track cooling ages from 50 samples, analyzed in conjunction with published fission-track data from the region, indicate a distinct population of young (Miocene) fission-track ages and a population of irregularly distributed older (pre-Miocene) fission-track ages. Miocene (young population) fission-track ages become younger toward the west-indicating westward migration of the cooling front, consistent with well-documented Miocene extension of the Basin and Range Province. The younging pattern is also consistent with west-northwest displacement of the hanging wall of a crustal-scale extensional fault system and consequent progressive footwall exhumation. The active trailing edge of the hanging wall of this system generally coincides with Death Valley. Migration rates of the cooling front in the footwall of this system are on the order of 10-11 mm/yr. Based on the distribution of the Miocene fission-track ages, we interpret that the crustal faults that defined the eastern edge of the detachment system originated as separate normal faults that were linked by the formation of a transfer fault. Extrapolation of apatite fission-track closure ages from two transects across the eastern margin of the Death Valley region suggests that exhumation along the eastern margin of the system continues beneath Death Valley today.