Using Detrital Thermochronology and Thermal Modeling to Constrain Basin Burial, Orogenic Exhumation, and Paleogeography of the Magallanes Basin, Southern Andes
The Magallanes retroarc foreland basin of southern South America affords an excellent basin setting to explore complex sediment and source thermal histories using the emerging method of coupled zircon U/Pb dating and (U-Th)/He thermochronology. This study reports detrital thermochronology results from the Paleocene through middle Miocene Magallanes Basin strata. To quantify the magnitude of basin reheating and assess the range of plausible thermal histories for these sediments, we performed thermal modeling of detrital age distributions. The magnitude of basin reheating that we have documented appears to be unusual in foreland basins and suggests that burial of the Paleocene deposits was much deeper than previously thought based upon stratigraphic thicknesses. Modeling results suggest that Paleocene strata in the Magallanes Basin achieved burial temperatures between ~170-185°C between 65-40 Ma. In light of the thermal contrast above and below this unconformity, we suggest that up to 3 km of missing sedimentary section may be represented by this unconformity.
Thermochronology and modeling results from the Paleocene-middle Miocene stratigraphic section suggest that: (1) the Paleocene basin fill underwent much higher Eocene-Oligocene basin burial heating than previously recognized; (2) sediment recycling of Mesozoic basement zircons in Upper Cretaceous foredeep deposits was an important part of the thrust belt history and sediment source for the Oligocene-Miocene depocenter. Additionally, we document rapidly-cooled Paleogene zircons that were probably derived from erosion of extensive volcanic rocks that blanketed the orogen and have since been eroded. Coupled detrital zircon thermochronology and this innovative thermal modeling approach offers a simple and effective method to test geologic models based on sediment recycling in fold-thrust belt settings and post-depositional burial heating.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California