INVESTIGATING THE ROLE OF MULTI-PHASE DEFORMATION HISTORY ON TRIASSIC TO RECENT CRUSTAL EXHUMATION IN THE EASTERN CORDILLERA OF SOUTHERN PERU

The role of multi-phase deformation on the crustal evolution of continental margins and Cordilleran mountain ranges remains unclear. The central Andes have experienced Paleozoic orogenesis, Mesozoic rifting, and Late Cretaceous to modern Andean mountain building. Andean mountain building involves key transient events, including Eocene onset of low-angle subduction, Oligo-Miocene slab steepening, and Miocene–Pliocene surface uplift coupled with deep canyon incision along the Eastern Cordillera flank. This research project takes place in the Eastern Cordillera of the central Andes in southern Peru, and reconstructs the thermal evolution of Triassic plutonic rocks from intrusion to near surface exposure by integrating multiple geo- and thermochronometers in a single sample. New zircon U-Pb geochronologic data from a sample collected at ~4700 m.a.s.l. constrains ~220-230 Ma crystallization timing at mid-crustal depths. Apatite U-Pb results from the same sample reveal ~218 Ma cooling through the ~550-450ºC closure temperature. The >350° difference in temperature sensitivity of these two methods, along with the ~12-2 Ma difference between the timing, suggests a period of rapid cooling immediately after emplacement. This potentially requires significant unroofing during a phase of proposed extensional deformation that occurred after late Paleozoic mountain building. Diagnostic Eastern Cordillera detritus is detected in Jurassic siliciclastic rocks situated in the Western Cordillera, consistent with erosion of the Eastern Cordillera prior to the onset of Andean mountain building. Zircon and apatite (U-Th)/He results from the same sample reveal Eocene to Miocene cooling ages that span the episode of low-angle subduction, suggesting renewed and protracted exhumation focused in the Eastern Cordillera throughout Andean mountain building. These results have implications for reconstructing the magnitude of crustal extension associated with post-Paleozoic rifting, the crustal architecture inherited by the Andean orogen, and potential linkages between slab and upper plate processes during mountain building.