T049-0004
Investigating the thermal effects of Cordilleran processes on a retroarc foreland basin using thermochronometry, vitrinite reflectance, and carbonate clumped isotopes

Tuesday, 15 December 2020
Poster
Rebecca A VanderLeest, Oberlin College, Geology, Oberlin, OH, United States, Julie C Fosdick, University of Connecticut, Geosciences, Storrs, CT, United States, Theresa Schwartz, USGS, Geosciences & Environmental Change Science Center, Lakewood, CO, United States, Ethan G Hyland, North Carolina State University Raleigh, Department of Marine, Earth & Atmospheric Sciences, Raleigh, NC, United States and Maria Mastalerz, Indiana University, Bloomington, United States
Abstract:
We evaluate post-depositional heating in response to basin burial, orogenic growth, and fluid-flow during evolution of the continental lithosphere using detrital thermochronometry, vitrinite reflectance, and carbonate clumped isotope geochemistry data from the Paleogene Magallanes-Austral Basin (Chile/Argentina). The basin is an unusually hot retroarc foreland basin due to formation on attenuated crust and passage of asthenospheric slab windows. It contains a Paleogene erosional unconformity across which previous work has documented a significant thermal contrast.

Danian strata below the unconformity yield zircon (U-Th)/He (ZHe) dates ~26-200 Ma that suggest post-depositional heating and partial He loss. In contrast, Eocene strata directly above the unconformity yield ZHe dates ~51-107 Ma that suggest minimal He loss. Apatite (U-Th)/He (AHe) dates from both formations range from ~7-24 Ma and suggest AHe dates are fully reset. Vitrinite reflectance (% Ro) data from Sierra Baguales and Cerro Castillo study areas range from 0.39-1.17 % Ro and reveal an increase in heating along the Paleogene unconformity.

Inverse thermal history modeling of Late Jurassic zircons with ZHe, AHe, and % Ro data reveal sediment-source cooling ~60-160 Ma associated with Late Cretaceous orogenic deformation and unroofing. Modeled post-depositional heating of Danian strata suggest maximum burial temperatures of 40–170 °C (Paleocene) and 55-155 °C (latest Oligocene-early Miocene). For middle Eocene strata, burial temperatures are consistent with calcite cement formation temperatures (~62-92 °C) indicated by carbonate clumped isotopes, and δ18Osf values (+1.4 to +7.7‰) indicate an orogenic fluid source. These data, plus modeling results and cement textures, refine the magnitude and timing of thermal events across the unconformity. Further, they highlight the role of post-middle Eocene basin heating related to orogenically derived fluids during Oligocene-Miocene mountain building and elevated regional heat flow during asthenospheric window formation beneath Patagonia.

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