Thrust tectonics in the Fuegian Andes central belt: A detailed geometric-kinematic analysis and new thermochronological constraints

Abstract

New structural data from the central belt of the Fuegian Andes (Argentina), allowed us to constrain the geometry of a previously interpreted Cenozoic duplex thrust system that connects forelandwards with the frontal thrust-fold belt. This duplex developed between two main detachment horizons: a basal detachment between Jurassic rocks and pre-Jurassic basement, and a roof detachment between Jurassic rocks and the Lower Cretaceous sedimentary fill of the Rocas Verdes back-arc basin. The duplex constitutes an intermediate structural level within a multiple detachment thrust belt and covers deeper structures that accommodated crustal deformation during the Cenozoic evolution of the Fuegian Andes. New zircon and apatite fission track and (UTh)/He cooling ages from rocks within the duplex were modelled together with previously published data, finding time-temperature trajectories that indicate acceleration in cooling rates during the middle Eocene to earliest Miocene, but with more moderate rates than previously reported. This is interpreted as exhumation associated with rock uplift due to duplex thrusting in the hinterland and shortening transference to the foreland, where known contractional stages are as young as early Miocene, and Oligocene-Miocene increased supply of detritus from the eroded central belt is widely reported.