Plate detachment, asthenosphere upwelling, and topography across subduction zones

This study analyzes the topography across subduction zones, considering the separate contributions of the crust and the mantle lithosphere to the obse rved surface elevation. We have found a transition from a region where the overriding plate is coupled to the descending slab and pulled down along wi th it to a region where the overriding plate floats freely on the asthenosp here. When the subducting slab retreats oceanward rapidly this transition i s abrupt, and the edge of the overriding plate is uplifted. We propose that at some point during rapid slab rollback the overriding plate detaches and rebounds like a boat released from its keel. This event is associated with suction of asthenospheric material into the gap that is opened between the plates up to the base of the crust. As a result, the forearc uplifts, and magmatism in the are increases.