The role of the asthenospheric window and deglaciation on the present-day uplift of the southern Patagonian Andes

Abstract

The southern Patagonian Andes (~46-56°S) are well suited to investigate the tectonic vs. climatic interactions during mountain building. Oceanic subduction underneath the South America continent occurs jointly with the opening of an asthenospheric window and, during the late Cenozoic, the building and melting of the Patagonian Icefields. Although the asthenospheric window caused regional dynamic uplift estimated in the order of the tenths of mm per year during the last 3 Ma, the present-day uplift rates in the orogenic domain subject to glaciation are measured between ~10-40 mm/yr. These uplift rates are to a large extent related to the glacial rebound since the Little Ice Age (~ AD 1630), but the role of rheological mantle and lithospheric weakening due to the asthenospheric window is currently unconstrained. Here we use numerical thermo-mechanical modeling to estimate the uplift induced by deglaciation of an ice sheet accounting for the rheological effects of asthenospheric thermal anomalies. Our results show two main phases of rock uplift: 1) a rapid increase in the uplift rates below the ice sheet when deglaciation starts, and 2) stable positive uplift rates during the deglaciation. For any tested, plausible rheological setting, the maximum uplift rates is 30 mm/yr with thermal anomalies higher than 100°C. The higher the asthenospheric thermal anomaly, the higher and wider the uplift rates, which may also involve initially ice-free regions. Uplift rates similar to those observed today require an asthenospheric thermal anomaly of 150-200°C. We conclude that, although the driver of the present-day uplift rates is the deglaciation, the asthenospheric window largely controls its outstanding magnitude.