Apatite fission track ages from a ~2000 m elevation transect from the Patagonian fold and thrust belt (47.5¿S) allow us to quantify the denudational and orographic response of the upper plate to active ridge subduction. Accelerated cooling started at 17 Ma, predating the onset of ridge collision (14--10 Ma), and was followed by reheating between 10 and 6 Ma. Thermal modeling favors reheating on the order of 60¿C at ~28¿C/Ma due to east-migration of a slab window after the ridge-trench collision. Final rapid cooling since 4 Ma of ~18¿C/Ma (geothermal gradient of 14¿C/km) correlates with the presence of an orographic barrier and >1 km rock uplift in this region between 17.1 and 6.3 Ma. Increased precipitation and erosion since 4 Ma caused asymmetric exhumation, with 3--4 km on the leeside. Repeated crustal unroofing in response to active ridge subduction can explain the positive gravity anomaly south of the Chile Triple Junction.