Contraction And Exhumation Of The Western Central Andes Induced By Basin Inversion: New Evidence From "Pampean" Subduction Segment

In this study, we conducted an integrated analysis supported by previous regional and mesoscopic field observations, new U-Pb chronological data of synorogenic deposits and thermochronological data from syncontractional granitic rocks. The objective is understanding the main mechanism and timing of crustal uplift of the western Central Andes on the modern flat-slab segment of northern Chile. The first-order structural styles identified in several basins of northern Chile consisted mostly of large reverse-reactivated Mesozoic normal faults, which formed large kilometer-scale inverted anticlines and localized doubly verging basement reverse faults depending on the degree of tectonic inversion. The observations indicate that crustal shortening experienced in the region was distributed along with the pre-orogenic half-graben structures of the Triassic to Jurassic basement. The wide distribution of Upper Cretaceous-Paleocene synorogenic deposits over the syn-rift Mesozoic deposits along inverted structures in both the Coastal and Frontal cordilleras indicate that the Andean orogenesis in the region was initiated during this period. Our field and geochronological interpretations suggest that basin inversion of the ancient Mesozoic half-graben structures was frequently accompanied by the emplacement of Upper Cretaceous and Paleocene intrusive granitic bodies hosted in the core of the anticline and syncline folds. Their crystallization ages correlated with those reported by the synorogenic deposits, thereby suggesting that both basin inversion and magmatism occurred simultaneously. The thermal history of the intrusives also indicates that they were rapidly exhumed at 53-57 Ma, possibly during the final episodes of the basin inversion.