T23A-2919
Shortening Record in the Central Andean Plateau of Southern Peru: Basement Inversion, Thin-skinned Thrusting, and Geomorphic Response
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Nicholas Perez, University of Texas at Austin, Austin, TX, United States, Brian K Horton, University of Texas at Austin, Department of Geological Sciences and Institute for Geophysics, Austin, TX, United States, Nadine McQuarrie, University of Pittsburgh, Pittsburgh, PA, United States, Konstanze Stübner, University of Tübingen, Institut für Geowissenschaften, Tübingen, Germany and Todd Alan Ehlers, University of Tübingen, Tübingen, Germany
Abstract:
Variations in the inherited structural architecture along western South America influence the timing, magnitude, and style of Andean deformation and topographic evolution. New results from mapping, balanced cross-section construction, apatite and zircon (U-Th)/He thermochronology, and geomorphology spanning the Altiplano, Eastern Cordillera and Subandean zone of southern Peru define the role of Triassic rift inversion on Cenozoic deformation style, thrust belt kinematics, exhumation timing, and spatial variation of canyon incision. A minimum of 130 km (38%) shortening along a 200 km transect accommodated by thin- and thick-skinned structures involved selective reactivation of Triassic normal faults that fed slip to shallower detachments of thin-skinned fold-thrust systems. Map relationships define unique structural domains defined by inherited normal faults. In the Eastern Cordillera, new zircon (U-Th)/He results from a Triassic pluton reveal Oligocene-Miocene (~26-18 Ma) cooling, consistent with previously reported exhumation from ~40 km along strike to the NW. However, rapid ~15 Ma cooling revealed by new apatite (U-Th)/He data is ~11 Myr older than equivalent rocks in a similar structural setting ~40 km to the NW. This suggests a potential middle Miocene shift from synchronous to diachronous exhumation along strike. Modern fluvial profiles constructed along the Eastern Cordillera show a reduction in knickpoint elevations from SE to NW, suggesting more youthful uplift toward the NW, comparable to the spatial trend in apatite (U-Th)/He ages. The deformation front reached the Subandean zone by ~15 Ma, after the majority of reported deformation in the Eastern Cordillera and Altiplano. These variations in exhumation over such distances are consistent with multiple potential scenarios: a northward propagating wave of uplift, spatial variations in climatically driven incision, interactions with mantle dynamics, or complex structural geometries.
