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 arcmigration during Neogene changes in subduction. At 31?33°S, above the modern flat‐slab segment, spatialand temporal linkages between thin‐ and thick‐skinned foreland shortening, basement‐involvedexhumation of the main Cordillera, and lower‐crustal hinterland thickening remain poorly resolved. Weintegrate new geochronological and thermochronological data for thrust sheets and Neogene foreland basinfill with structural, sedimentological, and passive seismic results to reconstruct the exhumation historyand evaluate potential geometric linkages across structural domains. 40Ar/39Ar ages for volcanic horizonsand zircon U‐Pb ages for synorogenic clastic deposits in the Manantiales Basin constrain the minimumduration of synorogenic sedimentation to ~22?14 Ma. Detrital zircon age distributions record sequentialunroofing of hinterland thrust sheets until ~15 Ma, followed by eastward (cratonward) advance of thedeformation 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 blocksand basin partitioning by ~14?5 Ma, consistent with the timing of the Manantiales facies and provenanceshifts and a coeval (~12?9 Ma) pulse of thin‐skinned shortening and exhumation previously identified in theeastern foreland. Late Miocene?Pliocene (~8?2 Ma) cooling ages along the Chile‐Argentina border point tohinterland uplift during the latest stage of Andean orogenesis. Finally, geophysical constraints on crustalarchitecture and low‐temperature thermochronometry results are compatible with a hybrid thin‐ andthick‐skinned décollement spanning retroarc domains.