Subduction margin architecture, thermal structure and exhumation in the Central Andes of southern Peru

The Peruvian Andes provide a unique setting to investigate the effects of ridge subduction superposed on a long-lived orogen. The recent (<5 Ma) arrival of the aseismic Nazca Ridge at the subduction interface offers a natural laboratory to examine how flat-slab dynamics interact with crustal structures inherited from Cretaceous to Miocene Andean evolution. Because slab geometry strongly influences magmatism, seismicity, crustal shortening, exhumation, and topography, understanding the relationship between the Nazca Ridge flat slab and the overriding plate is essential for reconstructing Andean geodynamics. We investigated the threedimensional architecture and thermal structure of the Central Andes in southern Peru, highlighting the interplay between basement structure, Moho geometry, slab configuration, and thermal properties. Basement highs and lows acted as zones of weakness that localized deformation during Andean shortening. The subducting Nazca Plate shows strong along-strike variations in dip and continuity, influenced by plate kinematics and by the Nazca Ridge. These variations control mantle wedge development, arc magmatism, and deformation patterns in the overriding plate. Heat flow increases from northwest to southeast, reflecting a transition from flat-slab conditions to steep-slab subduction characterized by magmatism and elevated geothermal potential. The flat-slab configuration was investigated by an integrated two-dimensional geological and geophysical model extending ∼1,000 km across the Peruvian Andes to depths of ∼180 km. The model combines surface geology, structural reconstructions, stratigraphic constraints, and geophysical data with forward modeling of the Bouguer gravity anomaly. A density model based on petrological and pressure-temperature constraints was constructed to define the geometry and physical properties of the subduction system at depth. Sampling for low-temperature thermochronology provided constraints on rock exhumation along the studied transect. Increasing exhumation rates during the last 5 Ma coincide with the transition from steep to flat slab caused by Nazca Ridge subduction. Our results reveal a strong contrast between deep and shallow deformation. At depth, the subduction system is dominated by the gently dipping to nearly horizontal Nazca Ridge slab, whose flat geometry enhances coupling between the Nazca and South American plates, promoting inland migration of deformation and increased upper-plate shortening. In contrast, the upper plate architecture is largely controlled by inherited rheological heterogeneities and preexisting structures related to earlier Andean tectonic phases. Crustal budget calculations yield shortening estimates between 137 km (25%) and 275 km (40%), depending on assumptions about pre-orogenic crustal thickness. Despite uncerta inties, these values are consistent with paleomagnetic reconstructions showing a northward decrease in shortening away from the Bolivian Orocline.