Andean Mountain Building and Foreland Basin Evolution During Thin‐ and Thick‐Skinned Neogene Deformation (32–33°S)

Abstract

The southern Central Andes recorded retroarc shortening, basin evolution, and magmatic arc migration during Neogene changes in subduction. At 31-33 degrees S, above the modern flat-slab segment, spatial and temporal linkages between thin- and thick-skinned foreland shortening, basement-involved exhumation of the main Cordillera, and lower-crustal hinterland thickening remain poorly resolved. We integrate new geochronological and thermochronological data for thrust sheets and Neogene foreland basin fill with structural, sedimentological, and passive seismic results to reconstruct the exhumation history and evaluate potential geometric linkages across structural domains. Ar-40/Ar-39 ages for volcanic horizons and zircon U-Pb ages for synorogenic clastic deposits in the Manantiales Basin constrain the minimum duration of synorogenic sedimentation to 22-14 Ma. Detrital zircon age distributions record sequential unroofing of hinterland thrust sheets until 15 Ma, followed by eastward (cratonward) advance of the deformation front, shutoff of western sediment sources, and a shift from fluvial to alluvial fan deposition at 14 Ma. Apatite (U-Th)/He cooling ages confirm rapid exhumation of basement-involved structural blocks and basin partitioning by 14-5 Ma, consistent with the timing of the Manantiales facies and provenance shifts and a coeval (12-9 Ma) pulse of thin-skinned shortening and exhumation previously identified in the eastern foreland. Late Miocene-Pliocene (8-2 Ma) cooling ages along the Chile-Argentina border point to hinterland uplift during the latest stage of Andean orogenesis. Finally, geophysical constraints on crustal architecture and low-temperature thermochronometry results are compatible with a hybrid thin- and thick-skinned decollement spanning retroarc domains.