New thermochronometric constraints on the rapid Palaeogene exhumation of the Cordillera Darwin complex and related thrust sheets in the Fuegian Andes

Thermal modelling of new fission‐track and (U–Th–Sm)/He data from the Fuegian Andes reveals rapid cooling (～12–48 °C Ma^?1) during the middle and late Eocene followed by slow cooling ( ～ 1.5 °C Ma^?1) to the Recent. We interpret the rapid cooling as a result of exhumation from contractional uplift within the crystalline interior of the orogen. This interpretation is consistent with independent evidence of Eocene shortening, flexural subsidence and provenance changes in the study area, and is approximately coeval with marine geochemical evidence of the onset of Drake Passage opening. In light of the Palaeogene history of Nazca‐South American plate convergence and the differences in shortening magnitudes and exhumation histories between the Fuegian and Patagonian Andes, our data support Eocene development of the Patagonian orocline, which also provides a plausible explanation for early opening of Drake Passage.