DECIPHERING SEDIMENT SOURCE EXHUMATION HISTORIES AND RATES TO THE PALEOCENE-EOCENE PALEO-RIO GRANDE RIVER SYSTEM FROM DETRITAL ZIRCON U-PB-HE DOUBLE DATING

Myriad provenance studies have constrained Paleogene sediment-routing pathways from North America to the Gulf of Mexico. However, provenance alone struggles to link sediment-routing system dynamics to tectonic and climatic forcing mechanisms. DZ U-Pb-He double dating allows for estimates of sediment source exhumation rates and mass fluxes from various sediment-routing segments, which is essential to understanding source-to-sink dynamics and estimating sediment budgets. The Paleogene Paleo-Rio Grande river system drained much of the SW US and N Mexico during Laramide deformation and major global climate change. Depth-profiled detrital zircons from Paleocene-Eocene fluvial-coastal marine strata in South Texas show that the Paleo-Rio Grande sourced sediment from Laramide volcanic centers and basement block uplifts in the SW US and recycled strata from the inverted Borderlands Rift in N Mexico. DZ U-Pb-He analyses show a diverse range of cooling ages due to the complex exhumation histories of these sediment source terranes. Eocene U-Pb ages yield Eocene cooling ages consistent with derivation from volcanic source terranes. Cretaceous-Paleocene U-Pb ages yield Cretaceous-Eocene cooling ages suggesting derivation from both the volcanic edifices and the progressively exhumed plutonic roots. Jurassic U-Pb ages yield cooling ages ranging from Jurassic to Eocene which overlap with Pangea/Borderlands rifting and inversion as well as the Sevier and Laramide orogenies. Mesoproterozoic-Paleozoic (Grenville to Peri-Gondwanan) U-Pb ages yield late Paleozoic-late Cretaceous cooling ages, consistent with the Alleghenian/Ouachita orogeny, Pangea/Borderlands rifting, and inversion. Paleo-Mesoproterozoic (Yavapai-Mazatzal) U-Pb ages yield late Triassic-Eocene cooling ages, consistent with the Sevier orogeny/Mogollon highlands and Laramide orogeny. Lag-times, the cooling age minus the depositional age, provide an idea of sediment source exhumation rates through the upper 6-8 km of the crust. Lag-times for Jurassic-Paleoproterozoic U-Pb ages are variable, from 0 to >100 Myr, demonstrating that the Paleo-Rio Grande was sourced from a broad suite of rapidly to slowly exhuming sediment source terranes complicated by sedimentary recycling and multi-stage exhumation histories.