TIMING AND DRIVERS OF EXHUMATION IN THE HINTERLAND OF THE NORTH AMERICAN CORDILLERA FROM DETRITAL ZIRCON U-PB AND (U-TH)/HE DOUBLE-DATING

The late Cretaceous to Cenozoic Nevadaplano is a well-recognized plateau that formed in the hinterland of the North American Cordillera. Although studies suggest that the Nevadaplano was in place by the Eocene, the exhumation history of the plateau and underlying drivers for development are not well understood. Thermochronology data from the western Great Basin and Sierra Nevada show a two-stage cooling history for the Nevadaplano. Although late Cretaceous exhumation fits well with the timing of deformation associated with the Sevier-Laramide orogeny, rapid exhumation in the Eocene is unexplained by the tectonic framework of the region. Rapid erosion in response to changing climate at the Eocene Climatic Optimum is a potential driver that has not yet been explored. This study will employ detrital zircon double-dating, pairing U-Pb and (U-Th)/He ages, to constrain the age, provenance, and depositional lag time of Eocene forearc and trench-slope sediments in the Great Valley and coast ranges in California. These sediment were likely sourced from the western Nevadaplano, and may provide valuable insight into the Eocene exhumational history of the region. To unravel exhumation histories, new detrital zircon U-Pb ages were obtained from 16 samples. For 13 of the samples, ~120-150 grains were picked for U-Pb analysis to confirm published provenance data and/or recover new provenance populations. Over 300 grains were selected and analyzed for the three remaining samples to confidently reveal all major source populations. Preliminary U-Pb data show most of the samples are predominantly sourced from two regions: the Jurassic and Cretaceous Sierra Nevada and Paleo- and Mesoproterozoic Mojave influence. The U-Pb data also reveal a spatial trend in potential source regions, with northern samples more strongly influenced by Sierran sources (some up to 100%), and southern samples more evenly mixed between Sierra Nevada and Mojave sources. To further elucidate grain cooling histories, their relationship to sediment source regions, and maximum depositional age, we will strategically analyze ~15-20 grains per sample from specific age-spectra peaks for (U-Th)/He dates. The combined dataset will provide valuable insight into the exhumation of the Nevadaplano and sediment source-to-sink histories.