GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 216-9
Presentation Time: 4:05 PM


KORTYNA, Cullen D., Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 2275 Speedway Stop C9000, Austin, TX 78712, STOCKLI, Daniel F., Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78712 and COVAULT, Jacob A., Bureau of Economic Geology, University of Texas at Austin, Austin, TX 78713

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.