HAS THE RECENT TECTONIC HISTORY OF PATAGONIA EQUIPPED IT WITH AN ANOMALOUS VISCOELASTIC RESPONSE TO CHANGING ICE LOADS?

Our geodetic measurements of vertical crustal motion in Patagonia indicate a broad pattern of uplift near the Patagonian Icefields, with maximum observed velocities of ~ 20 mm/yr. This rate of uplift is an order of magnitude larger than the expected level of postglacial rebound associated with the major deglaciation following the Last Glacial Maximum. It can be explained if, as anticipated by Ivins and James (1999), the unusual tectonic setting of this region equips it with a short isostatic response time and an extraordinary sensitivity to the neoglacial fluctuations caused by Late Holocene climate change. A short isostatic response time implies that anomalously low viscosities occur in the asthenosphere. This ‘hot and weak' mechanical scenario is plausible given the tectonic setting of the Patagonian Andes. The large volumes of late Miocene to Pleistocene plateau lavas that have erupted into the present backarc region east of the Andes between about 46° S and 52° S are widely believed to manifest a ‘slab window' associated with the Chile Rise triple junction. In this presentation we review the geodetic constraints and consider whether or not the rebound field can be explained in any other way.