Slab-driven Mantle Weakening and Rapid Mantle Flow

This chapter presents a series of two-dimensional models of subduction are presented to investigate parameters controlling slab-induced mantle weakening and increased mantle flow rates in a simplified tectonic setting. Models using the composite viscosity formulation produce a zone of subduction-induced mantle weakening that results in reduced viscous support of the slab. In all cases, the magnitude of induced mantle flow is larger in the models using the composite viscosity formulation. The models suggest that the slab-driven mantle weakening and localized increased mantle flow phenomenon occurs in most subduction zones, and is primarily modulated by the mantle deformation mechanism, slab strength, and slab buoyancy, as suggested in 3D regional and global models. The results are consistent with three-dimensional models of subduction with a composite rheology and show that the rapid mantle flow predicted by these models is not due to the proximity of the model sidewalls.