A Review of the Role of Subduction Dynamics for Regional and Global Plate Motions

Subduction of oceanic lithosphere and deep slabs control several aspects of plate tectonics. We review models of subduction dynamics that have been Studied over the last decade by means of numerical and analog experiments. Regional models indicate that trench rollback, trench curvature, and back-arc deformation may be explained by fluid slabs that are similar to 250-500 times stiffer than the upper mantle. Slab width and, more importantly, rheology determine the role of viscous bending, poloidal-sinking flow and toroidal-rollback stirring, and interactions of the slab with the higher viscosity lower mantle. Several of these contributions call be represented by a local sinking velocity. Back-arc deformation may then result from ail imbalance if larger-scale plate forcing leads to deviations of the convergence rate from the local equilibrium. Lateral viscosity variations (LVVs) are also key for understanding plate driving forces. The realism of global circulation computations has advanced and such models with weak zones and other LVVs have lead to an improved match to observed plate tectonic scores. Those include the correlation with plate motions, the magnitude of intraplate deformation, and oceanic to continental plate velocity ratios. Net rotation of the lithosphere with respect to the lower mantle may be Caused jointly by regional slab forcing and the stirring effect of cratonic keels. However, slab models have so far only produced net rotations that are small compared to recent hotspot reference-frame models. Progress in the next years will likely come from a better understanding of slab strength, which is still uncertain since large-scale subduction zone observables and laboratory results do not put strong constraints oil slab rheology. Importantly, circulation models with ail improved representation of convergent margins will help to close the gap between regional and global approaches to subduction, and to better understand the potential role of the overriding plate.