Eastern Section Meeting

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Thermal history of the Maastrichtian – Eocene Magallanes (Austral) foreland basin, Patagonia (50.5 – 51.5° S): Preliminary findings from vitrinite reflectance analysis and detrital zircon thermochronology


We report new vitrinite reflectance data and detrital zircon (U-Th)/He thermochronology from Maastrichtian through lower Eocene strata of the Magallanes foreland basin in Patagonia to investigate thermal effects of sedimentary burial and transient heating from fluid flow or magmatism on the tectonic history of the foreland region during Patagonian orogenesis. Although retroarc foreland sedimentation was continuous further south in Tierra del Fuego during this time period, the basin record in the Patagonian sector includes several enigmatic unconformities, including a basin-wide Paleogene unconformity. However, the age, duration, and geologic significance of this unconformity remain under debate.

Vitrinite reflectance analysis of 11 samples from organic-rich samples yield values between 0.5 – 0.6 % in the Río Baguales section and values between 0.4 – 0.5% in the Cerro Castillo section along-strike to the south. Maximum temperatures calculated from the Río Baguales data range from ~65.5 to 101.9°C, whereas temperatures of 71 to 85°C are calculated for the Cerro Castillo section. These results suggest that the Río Baguales area experienced higher temperatures than strata exposed near Cerro Castillo. The Río Baguales data show inverted temperatures that are cooler at the bottom and higher up-section, suggesting that a simple burial mechanism is not sufficient to explain the data. These spatial and stratigraphic temperature variations could be derived from fluid heat flow, magmatism or elevated radioactive decay.

In order to characterize the timing and duration of post-depositional heating, we performed (U-Th)/He thermochronology of detrital zircon collected from four samples that span Paleocene - Eocene deposits. Preliminary data suggest both spatial