Low-temperature thermochronology of the Black and Panamint mountains, Death Valley, California: Implications for geodynamic controls on Cenozoic intraplate strain

We use apatite and zircon (U-Th)/He thermochronometry to evaluate space-time patterns and tectonic drivers of Miocene to Pliocene deformation within the Death Valley area, eastern California. Zircon He ages from the footwall of the Amargosa-Black Mountains detachment in the Black Mountains record continuous cooling and exhumation from 9 to 3 Ma. Thermal modeling of data from the central Black Mountains suggests that this cooling took place during two intervals: a period of rapid footwall exhumation from 10 to 6 Ma, followed by slower (<5 mm/yr) exhumation since 6 Ma. Cumulative exhumation is estimated to be 10-16 km. Paleodepth reconstruction of cooling ages from the footwall of the Panamint-Emigrant detachment, in the central Panamint Range, also show two periods of cooling. Zircons record late Miocene cooling, whereas apatite He ages show punctuated exhumation at ca. 4 Ma. The results suggest the Panamint Range experienced a minimum of 7.2 km of exhumation since ca. 12 Ma. The new data, when evaluated within the context of published fault timing data, suggest that the transition from Basin and Range extension to dextral transtension is spatially and temporally distinct, beginning at ca. 11-8 Ma in ranges to the east and north of the Black Mountains and migrating westward into eastern Death Valley at 6 Ma. Initiation of dextral transtension was coincident with a major change in plate-boundary relative motion vectors. Data from Panamint Range and several ranges to the west of Death Valley indicate transtension initiated over a large area at ca. 3-4 Ma, coeval with proposed lithospheric delamination in the central and southern Sierra Nevada Range. Our results suggest that the transition from extension to dextral transtension may reflect an evolution in tectonic drivers, from plate-boundary kinematics to intraplate lithospheric delamination.