The global range of subduction zone thermal models

Abstract

We model 56 segments of subduction zones using kinematically defined slabs based on updated geometries from Syracuse and Abers (2006) to obtain a comprehensive suite of thermal models for the global subduction system. These two-dimensional thermal models provide insight to the dehydration and melting processes that occur in subduction zones. Despite the wide range of slab geometries, ages, convergence velocities and upper plates the predicted thermal structures share many common features. All models feature partial coupling between the slab and the overriding plate directly downdip of the thrust zone, invoked to replicate the cold nose observed in measurements of heat flow and seismic attenuation. We test four separate assumptions about the causes of the partial coupling: (1) the downdip end of the partial coupling is at a constant depth, (2) it is at constant distance trenchward from the arc, (3) it is defined by a critical surface slab temperature, or (4) it is adjusted such that the hottest part of the mantle wedge beneath the arc is at a constant temperature for all subduction zones. In all of these models, slabs reach temperatures where the top of the oceanic crust and sediments dehydrate before they reach subarc depths, and the overlying mantle wedge is too hot for hydrous minerals to be stable at subarc depths. By contrast, the interior of the oceanic crust and underlying mantle within the downgoing plate remains cold enough for hydrous phases to be stable beyond the arc in all but the hottest subduction zones, allowing water to be carried beyond the arc in the slab.