Exhumation response to climate and tectonic forcing in the southern Patagonian Andes (Torres del Paine and Fitz Roy plutonic complexes)

Alpine landscapes form in mountain belts that likely experienced tectonic uplift during plate’s convergence, and efficient erosion dominated by glacial carving and circle retreat. In southern Patagonia N-S oriented late Miocene plutonic complexes are exposed in deep incised valleys with summits topographically above the glacial equilibrium line altitude. Two of the most emblematic ones are the Fitz Roy (Chaltén, latitude 49°S) and the Torres del Paine (latitude 51°S) plutonic complexes, ~2 km higher than the mostly flat bottom valley that is partially covered by the Southern Patagonian Icefield. This continental region is located above an asthenospheric window that opens and migrates from the latitude 54 °S towards the latitude 46 °S since ~16 Ma, and experienced dynamic uplift during episodes of spreading ridge collision with the continental margin. Here we present a new dataset of combined low-temperature thermochronometers from the Chaltén and Torres del Paine plutonic complexes, and their thermal history inversion numerical modeling, to identify the geodynamic processes forcing on the exhumation of the mountain belt. These complexes are separated by 200 km along the strike of the belt, and share a pulse of rapid exhumation at ca. 6 Ma, likely showing that glaciation was regionally starting at this moment. After a period of quiescence, in Torres del Paine the exhumation rate is accelerated from ~2 Ma to the present, interpreted as a signal of the Pleistocene climatic transition creating incise valleys. Only in the Fitz Roy a pulse of rapid exhumation is present at ca. 10 Ma, approximately coincident with the time range in which the ridge was subducting beneath the continent at that latitude. This allows us to separate the climatic from the tectonic/mantle forcing to the exhumation in southern Patagonia, and represents the first in-situ observation of the passage of the asthenospheric window in the low-temperature thermochronometric record of the region.