BASIN EVOLUTION AND SURFACE UPLIFT OF THE HUACOCHULLO AND PUQUIO REGIONS IN SOUTHERN PERU THROUGH ZIRCON U-PB GEOCHRONOLOGY AND VOLCANIC GLASS PALEOALTIMETRY

Geodynamic models describing the formation of the central Andean plateau show either rapid or steady topographic rise driven by incremental or rapid removal of dense lithospheric material, respectively. Wholesale or piecemeal foundering of mantle lithosphere predicts pulses of surface uplift that may be uncorrelated with steady crustal shortening, and where the surface expression scales with the scale of the foundering block. Lithospheric removal by ablative subduction or thermal weakening predicts slower uplift that is spatially and temporally coincident with crustal shortening. Distinguishing between these models requires integrating the subsidence and deformation history of hinterland basins with the record of uplift and formation of the central Andean plateau. Research on these topics has been focused in Bolivia and Argentina; there has been relatively little investigation in southern Peru.

We present new stratigraphic, geochronologic, and stable isotopic data for temporally overlapping, yet spatially separate Cenozoic intermontane basins of southern Peru (specifically, the Huacochullo and Puquio regions in the northernmost Altiplano and Western Cordillera). In the context of newly logged stratigraphic sections, these data place constraints on reconstructions of rate and distribution of Cenozoic deformation and intermontane basin filling, and give insight into the uplift history of the northern extent of the central Andean plateau. We document the former through basin analysis combined with published records of timing of crustal shortening, and the latter using a novel approach to paleoaltimetry via stable isotope analysis of deuterium (²H) in hydrated volcanic glass. Because water-glass isotopic fractionation during hydration is temperature-independent, volcanic glass paleoaltimetry circumvents one potential complication highlighted by recent advances in climate simulations: non-adiabatic decreases in temperature with rising topography. Guided by such advances, our preliminary results suggest rapid uplift need not be coupled with crustal shortening in the northwestern Altiplano and Western Cordillera, and are consistent with a geodynamic mechanism involving piecemeal foundering of mantle lithosphere.