Fast uplift in the southern Patagonian Andes due to long-and short-Term deglaciation and the asthenospheric window underneath

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 g 1/426000gBP (years before present). Significant deglaciation onsets between 21g 000 and 17g 000gBP were subject to an acceleration since the Little Ice Age (LIA), which was g 1/4400gBP. Fast uplift rates of up to 41±3g mmg yr-1 are measured by global navigation satellite system (GNSS) around the Southern Patagonian Icefield and are currently ascribed to post-LIA lithospheric rebound, but the possible longer-Term post-LGM rebound is poorly constrained. These uplift rates, in addition, are 1 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 post-glacial rebound matches the observed uplift rate budget only when both post-LIA and post-LGM deglaciation are accounted for and only if a standard continental asthenospheric mantle potential temperature is increased by 150-200g °C. The asthenospheric window thus plays a key role in controlling the magnitude of presently observed uplift rates in the southern Patagonian Andes.