The temperature structure of a subduction zone, including convection in the surrounding asthenosphere and dehydration and frictional heating in the descending slab, has been calculated by a finite difference procedure. Models of ocean-ocean (thin landward lithosphere) and ocean-continent (thick landward lithosphere) convergence have been constructed. In the ocean-ocean case, melting is predicted only in the wet-peridotite of the asthenosphere overlying the downgoing slab. In the ocean-continent case, however, melting of the lower continental mantle, the basal continental crust, and the subducted oceanic crust as well as the asthenosphere above the slab could occur. A complex origin for continental volcanic arc magmas is permitted by this model. Additionally, a change in focal mechanisms from interplate thrust to intraplate compression and a zone of high b-values (the frequency-magnitude relation of earthquakes) in the upper of two seismic planes delineating the subducting Pacific Plate beneath northeastern Honshu, Japan, both occur where dehydration of the oceanic crust is predicted to occur in our model. The coincidence between the location of the dehydration front in the slab and the existence of an aseismic front in the wedge above this dehydration boundary suggests that water advecting upward from the slab prevents the occurrence of earthquakes. Temperatures in this region between the aseismic front and the volcanic front are too cold to allow melting of wet peridotite to occur, but beneath the volcanic front, melting of wet asthenosphere is predicted.
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DeLong et al. (1980) studied this question.