CONVERGENT OROGENESIS IN THE SOUTHERN PATAGONIAN ANDES AND MAGALLANES-AUSTRAL BASIN (Invited Presentation)

The Upper Cretaceous through Cenozoic Magallanes-Austral Basin, Chile and Argentina, chronicles Andean orogenesis and foreland sedimentation during major plate reorganization surrounding southern South America. Key events include closure of the Rocas Verdes backarc basin and arc-continental collision, growth of the Patagonian retroarc fold-and-thrust belt during Andean-style subduction, middle Cenozoic opening of Drake Passage, and the subduction of Eocene and middle Miocene mid-ocean ridge spreading centers beneath Patagonia. This contribution summarizes new sedimentary provenance analysis, stratigraphy, and thermochronology in the Magallanes-Austral Basin exploring the effects of these changing plate boundary processes on fold-and-thrust belts. The Upper Cretaceous retroarc depocenter was uplifted during Cenozoic deformation and eastward shift of foredeep subsidence. Kinematic reconstructions show a change from Late Cretaceous-Paleogene thin-skinned deformation to late Oligocene- early Miocene reactivation of reverse faults. Basinwide disconformities and the paucity of Paleocene strata suggest that the Paleogene foreland was characterized by laterally discontinuous subaerial exposure, localized subsidence, and deposition of sediment derived from the widening thrust-belt. Sedimentary provenance data from the Cenozoic basin infill document the continued uplift and progressive isolation of deeply eroded hinterland thrust sheets. Upsection changes in sediment composition, along with stratigraphy, subsidence patterns, and unconformities, suggest a strong impact on foreland basin evolution from the subduction of mid-ocean ridges beneath the South American Plate and associated changes in stress regime.