Cenozoic Thermal Evolution of the Darwin Complex and Related Terranes in Tierra Del Fuego

Because of its proximity and common history for much of the Mesozoic and Cenozoic, Tierra del Fuego should provide insight into the tectonic history of the Antarctic Peninsula. In this study, we examine the thermal history of structurally deep units of the Fuegian thrust-belt using fission-track, (U-Th)/He, and U/Pb thermochronometry of apatite and zircon. Six samples were collected from the study area, including from the amphibolite-facies Darwin Complex, granitoids intruding the Yahgan Formation on each side of the Beagle Channel, and the Yahgan and Tobífera Formations of the Cerro Verde thrust sheet. Cooling as slow as 2ºC/Myr, punctuated by short bursts of comparatively rapid cooling of 10-20ºC/Myr were recorded in most of the samples. The period of rapid cooling occurred from 70-35 Ma depending upon location, with an apparent peak between 45 and 50 Ma. A more ambiguous second cooling event is suggested by ages spanning 25-3 Ma. The approximate coincidence of this exhumation, a similar thermal history in the northern Antarctic Peninsula, and the arrival of Pacific seawater in the Atlantic sector of the Southern Ocean suggest a genetic relationship with opening of adjacent Drake Passage.