THE ROLE OF STRUCTURAL INHERITANCE AND SELECTIVE REACTIVATION ON ANDEAN MOUNTAIN BUILDING IN SOUTHERN PERU (Invited Presentation)

A new synthesis of the timing, position, and style of deformation spanning the Andes of southern Peru reveals how pre-Andean extensional basins were selectively reactivated and inverted during Andean orogenesis. The forearc and Western Cordillera contain a newly recognized bivergent thick- and thin-skinned fold thrust belt that initiated by ca. 70 Ma and accommodated shortening through the mid-Miocene. In the forearc, selective reactivation of an inherited normal fault and relatively low Andean shortening magnitude correspond to a segment of the fold-thrust belt that inverted a Jurassic backarc basin. In the Western Cordillera, higher shortening magnitudes are accommodated by thin-skinned imbricates and duplexes that developed across the Andean volcanic arc. The timing of deformation is established at multiple structures and reveals that shortening in the forearc and Western Cordillera was coeval with the timing of deformation in the Eastern Cordillera. The Eastern Cordillera reactivated an inherited Permo-Triassic rift basin, exhibits selective reactivation of basin margin structures, and shows that shortening was partitioned into zones of relatively low and high magnitudes delineated by inherited structures. Out-of-sequence basement-involved shortening in the Western Cordillera during the late Miocene to Pliocene localized ca. 4 km of incision and development of one of Earth’s deepest canyons, Cañon de Colca. The emerging synthesis shows that this segment of the Andes experienced distributed and out-of-sequence deformation spanning at least the Eocene to Miocene, with loci of fold-thrust belt deformation reactivating pre-Andean extensional basins. Inherited extensional basins in the Western and Eastern Cordilleras play key roles in the timing, style, position, and magnitude of cordilleran mountain building.