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Abstract

Modern geodetic techniques, such as the precise Global Positioning System (GPS) and high-resolution space gravity mapping (GRACE and GOCE), make it possible to measure the gravitational--viscoelastic earth response to ongoing and past glacial changes. The Andes of Patagonia feature glacial environments of dramatic ice-mass changes near a tectonically active boundary between the Antarctic and South American plates. The mechanical strength of the continental side of this boundary is influenced by Pliocene ridge subduction and by the current subduction of a youthful oceanic slab. A chain of young volcanos strikes parallel to the Pacific coastline. The release of volatiles, such as water below the volcanoes, creates a unique rheological environment modelled by a low-viscosity wedge between the slab and the continental lithosphere. To assess the influence of this laterally inhomogeneous structure on the isostatic adjustment process due to present and past ice-mass changes, we first develop a two-dimensional viscoelastic earth model. In a numerical study, we then examine the variability of the glacial loading--unloading response caused by the presence of the subducting slab and the mantle wedge. We find that the slab restricts the material transport to the oceanic side, depending on its mechanical strength and penetration into the upper mantle. The reduced viscosity inside the mantle wedge enhances the load-induced material transport everywhere inside the asthenosphere.