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Abstract

Models seeking to explain the evolution of the globally unique central Andean Altiplano–Puna Plateau have invoked both a single, kinematically linked, retro-arc orogenic wedge, or two kinematically distinct orogenic wedges. In this study, I examine these two hypotheses in a critical taper theory framework; examining whether the subsidence and exhumation is consistent with one or more than one orogenic wedge. The first proposes that the entire orogen acted as a single wedge advancing eastward. Alternatively, the orogen comprises two separate, kinematically distinct wedges. I test these hypotheses by integrating maximum depositional ages (MDAs), provenance data, and double dated detrital zircon geochronology and thermochronology (U-Pb and U-Th/He) from four stratigraphic sections at ~16°S on the western and eastern sides of the northern Altiplano Basin to determine changes in source region exhumation through lag time analysis. Depositional ages in sections span the Late Cretaceous to late Eocene. Lag time analysis showed that an early exhumation pulse at ~48 Ma marks the initiation of an eastern wedge corresponding to the proto–Eastern Cordillera (EC), while a later frontal advance of the Western Cordillera (WC) at ~35 Ma reflects a separate western wedge system. Provenance data show a transition from Paleocene–early Eocene WC and Altiplano sources to an influx of EC detritus by ~48 Ma, consistent with initial exhumation of the eastern wedge. By ~35 Ma, both basin margins record contributions from both wedges, consistent with regional dominance of EC sources. Chronostratigraphic correlations across the basin reveal Paleocene flexural subsidence focused along the western margin, followed by laterally uniform early–middle Eocene deposition, indicating a transition from single sided foredeep loading to dual loading by both WC and EC. Considered together, these results are inconsistent with models of the central Andes as a single, eastward-advancing orogenic wedge. Instead, they are consistent with asynchronous growth and evolution of two critically tapered wedges centered on the Western and Eastern cordilleras. I attribute formation of the eastern wedge to reactivation of inherited lithospheric heterogeneities.