Present-day uplift of the western Alps
Résumé
Collisional mountain belts grow as a consequence of continental plate convergence and eventually
disappear under the combined effects of gravitational collapse and erosion. Using a decade of
GPS data, we show that the western Alps are currently characterized by zero horizontal velocity
boundary conditions, offering the opportunity to investigate orogen evolution at the time of
cessation of plate convergence. We find no significant horizontal motion within the belt, but GPS and
levelling measurements independently show a regional pattern of uplift reaching ~2.5 mm/yr in the
northwestern Alps. Unless a low viscosity crustal root under the northwestern Alps locally enhances
the vertical response to surface unloading, the summed effects of isostatic responses to erosion and
glaciation explain at most 60% of the observed uplift rates. Rock-uplift rates corrected from transient
glacial isostatic adjustment contributions likely exceed erosion rates in the northwestern Alps. In the
absence of active convergence, the observed surface uplift must result from deep-seated processes.
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