Fast uplift in the Southern Patagonian Andes due to long and short term deglaciation and the asthenospheric window underneath

Abstract

Abstract. An asthenospheric window underneath much of the South American continent increases the heat flow in the Southern Patagonian Andes, where glacial-interglacial cycles drive the building and melting of the Patagonian Icefields since the latest Miocene. The Last Glacial Maximum (LGM) was reached ~20000 years ago, and an acceleration of the deglaciation rate is recorded since the Little Ice Age (LIA), ~400 years ago. Fast uplift rates of up to 41±3 mm/yr are measured by GNSS around the Southern Patagonian Icefield and currently ascribed to post-LIA lithospheric rebound, but the possible longer-term post-LGM rebound is poorly constrained. These uplift rates, in addition, are one order of magnitude higher than those measured on other glaciated orogens (e.g., the European Alps), which raises questions about the role of the asthenospheric window in affecting the vertical surface displacement rates. Here, we perform geodynamic thermo-mechanical numerical modelling to estimate the surface uplift rates induced by post-LIA and post-LGM deglaciation accounting for temperature dependent rheologies and different thermal regimes in the asthenosphere. Our modelled maximum postglacial rebound matches the observed uplift ratebudget only when both post-LIA and post-LGM deglaciation are accounted for and if a standard continental mantle potential temperature is increased by 150–200 °C. The asthenospheric window thus play a key role in controlling the magnitude of presently observed uplift rates in the Southern Patagonian Andes.