PALEOGENE PROVENANCE AND TECTONICS OF FUEGIAN ANDES REVEALED BY THE HEAVY MINERAL ANALYSIS FROM THE EASTERN MAGALLANES FORELAND BASIN

Provenance analysis by testing temporal variations in heavy mineral composition of basinal sediments is a useful mean to reconstruct the kinematic history of associated orogenic systems. We report the results of heavy minerals analysis from a near-continuous upper Cretaceous to lower Miocene succession from the eastern Magallanes foreland basin of southernmost South America. Although southern South America and the Antarctic Peninsula were previously connected through a Paleozoic-Mesozoic subduction system on the western margin of Gondwana, this connection was tectonically disrupted in the Cenozoic by forming the Drake Passage in the Scotia Sea. Our reported data reveal a dramatic shift in sediment provenance at the middle to late Eocene time (ca. 39 Ma) in Fuegian Andes hinterland. Heavy mineral data indicate that Campanian to middle Eocene sediments of Magallanes basin had a mafic/ophiolitic provenance, derived from the magmatic arc and marginal basin mafic complex. Upper middle Eocene to lower Miocene sequences, on the other hand, suggest a metamorphic/ metasedimentary provenance indicating rapidly exhumed Cordillera Darwin metamorphic complex as the sediment source. These data are consistent with recent interpretations of the basin's detrital-zircon geochronology as evidenced by increased Eocene tectonic exhumation, and providing further support for temporal and possibly genetic relationships between development of the Patagonian orocline and the opening of Drake Passage.