The Patagonian Andes represents a unique natural laboratory to study surface deformation in relation to deep slab dynamics. In the sector comprised between latitudes 41°30′ and 43°S, new apatite (U‐Th)/He ages indicate a markedly different unroofing pattern between the “broken foreland” area (characterized by Late Cretaceous to Paleogene exhumation) and the adjacent Andean sector to the west, which is dominated by Miocene‐Pliocene exhumation. These unroofing stages can be confidently ascribed to inversion tectonics involving reverse fault‐related uplift and concomitant erosion. Late Cretaceous‐Paleogene shortening and exhumation are well known to have affected also the thrust belt sector of the study area during a prolonged stage of flat‐slab subduction. Therefore, the different ages of near‐surface unroofing documented in this study suggest coupling of the deformation between the thrust belt and its foreland during periods of flat‐slab subduction (e.g., during Late Cretaceous‐Paleogene times) and dominant uncoupling during periods of steep‐slab subduction and rollback, even when these are associated with high convergence rates (i.e., > 4 cm/yr), as those documented in Miocene times for the Patagonian Andes.

In cordilleran-type orogens, subduction geometry exerts a fundamental control on the tectonic behavior of the overriding plate. An integrated low-temperature, large thermochronological data set is used in this study to investigate the burial and exhumation history of the overriding plate in northern Patagonia (40°−45°S). Thermal inverse modeling allowed us to establish that a ∼2.5−4-km-thick section originally overlaid the Jurassic−Lower Cretaceous successions deposited in half-graben systems that are presently exposed in the foreland. Removal of the sedimentary cover started in the late Early Cretaceous. This was coeval with an increase of the convergence rate and a switch to a westward absolute motion of the South American Plate that was accompanied by shallowing of the subducting slab. Unroofing was probably further enhanced by Late Cretaceous to early Paleogene opening of a slab window beneath the overriding plate. Following a tectonically quiescent period, renewed exhumation occurred in the orogen during relatively fast Neogene plate convergence. However, even the highly sensitive apatite (U-Th)/He thermochronometer does not record any coeval cooling in the foreland. The comparison between Late Cretaceous and Neogene exhumation patterns provides clear evidence of the fundamental role played by inter-plate coupling associated with shallow slab configurations in controlling plate-scale deformation. Our results, besides highlighting for the first time how the whole northern Patagonia foreland was affected by an exhumation of several kilometers since the Late Cretaceous, provide unrivalled evidence of the link between deep geodynamic processes affecting the slab and the modes and timing of unroofing of different sectors of the overriding plate.

No abstract

No abstract