EXHUMATION OF THE LARAMIDE HINTERLAND AND SEDIMENT DELIVERY TO THE GULF OF MEXICO: INSIGHTS FROM DETRITAL ZIRCON (U-TH)/(HE-PB) DOUBLE DATING (Invited Presentation)

Reconstructing source-to-sink linkages between the Laramide hinterland and the paleo-Rio Grande fluvial axis along the Gulf Coast is challenging because: a) exhumation and erosion of sediment source regions in the Mojave-Sonoran Desert region are poorly constrained; b) the nature of the Laramide landscape and topography is speculative; and c) the region lacks a well-preserved, proximal sedimentary record of Laramide orogenesis. Detrital zircon (U-Th)/(He-Pb) double dates (246 dates from 14 samples) from Late Cretaceous–Eocene fluvial strata of the Tornillo basin, west Texas and fluvial-to-marginal marine strata of the Rio Grande embayment, south Texas refine sedimentary provenance, elucidate sediment source exhumation, and allow for the estimation of source region erosion rates and sediment supply. The detrital zircon (U-Th)/He data are dominated by Late Cretaceous–Eocene (67% and 65%, respectively) dates with subordinate Jurassic–Early Cretaceous (~31% and ~24%) and minor Permian–Triassic and Neoproterozoic–Paleozoic components. In detail, the (U-Th)/(He-Pb) double dates can be broken into two general time-temperature histories: a) exhumation during Border rifting and Sevier orogenesis and subsequent recycling out of the Sevier foreland and Border rift basins during Laramide inversion, uplift, and erosion; and b) first-cycle exhumation and erosion of Cordilleran and Laramide arc magmatic rocks and Yavapai-Mazatzal basement in Laramide basement-cored reverse faulting. The first-cycle zircons exhibit short mean steady lag times between 7 and 17 Myr indicating that the Mojave-Sonoran Desert region was experiencing rapid cooling and exhumation during Laramide orogenesis. We invert the distribution of lag times to estimate erosion rates for U-Pb-fingerprinted sediment source regions and sum the erosional contributions from each source region to estimate sediment supply. Estimated erosion rates indicate that the Mojave-Sonoran Desert region saw significant Paleocene–Eocene exhumation in a rapidly eroding, mountainous Laramide landscape. The estimated sediment loads are significantly larger than previous estimates of Paleocene sediment delivery to the paleo-Rio Grande but are consistent with major Carrizo-Rosita fluvial-deltaic sedimentation in the early Eocene.