Spatiotemporal evolution of a newly recognized Late Cretaceous fold-and-thrust belt in the western slope of southern Peru: Evidence for selective inversion and hybrid thick- and thin-skinned shortening

A series of cross sections, field relationships, and geochronologic and thermochronologic constraints demonstrate the existence of a Late Cretaceous−Miocene hybrid thick- and thin-skinned fold-and-thrust belt in the Western Cordillera of southern Peru (15°S−16°S). Shortening in the eastern half of the central Andes has been thoroughly investigated, but in southern Peru, the timing, position, and style of deformation within the western slope during Andean orogenesis remain poorly constrained. Thermal modeling of zircon fission-track results and the zircon and apatite (U-Th)/He data from the hanging wall of a northeast-verging basement-involved reverse fault in the Western Cordillera demonstrate rapid cooling from ca. 75 Ma to 55 Ma. We propose this cooling history reflects the onset, or continuation, of contractional deformation and is the earliest quantitative record of shortening in southern Peru. In the footwall of this structure, we documented a thin-skinned duplex and a fault-bend fold, attesting to the linkage within this hybrid thick- and thin-skinned fold-and-thrust belt. In the forearc, crosscutting relationships reveal a reactivated normal fault that was inverted during the Oligocene, part of a southwest-verging domain that constitutes the other flank of this fold-and-thrust belt and highlights the role of selective reactivation of preexisting structures. Timing constraints on other structures reveal spatially distributed deformation spanning the forearc and Western Cordillera during the Eocene to Miocene. The resulting interpretations highlight diverse structural styles, inherited structures, and distributed out-of-sequence deformation across the northern central Andes of southern Peru, which have implications for the spatiotemporal distribution and style of deformation throughout the central Andes.