Influence of lithosphere‐asthenosphere interaction on the overriding lithosphere in a subduction zone: Numerical modeling

Several factors influence the topography of the overriding plate in a subduction zone: mantle wedge flow caused by motion of the descending slab, lithosphere elasticity, and interaction between the solid lithosphere and the viscous asthenosphere. This paper presents the results of new subduction modeling that incorporates both elastic/elastoplastic deformation in the overriding plate and viscous deformation in the asthenosphere. The effects of fluid‐solid coupling and interaction were considered using an arbitrary Lagrangian‐Eulerian technique that solves for the continuous deformation of fluid flow in contact with the rigid plate. Modeling results show that thicker lithosphere, which is harder to deform, contributes to the development of broadly shallower back‐arc basins. As lithospheric strength decreases, its ability to withstand outside force (fluid load) resulting from flow in the mantle wedge also declines, leading to the development of deep and narrow basins. Large‐scale deformation of the lithosphere modifies both the mantle wedge geometry and the wedge flow pattern, which in turn increases the fluid load and thereby enhances topographic variation. Generally, the effect of interaction is enhanced with lithospheric deformation. The elastoplastic model also leads to a weaker lithosphere and a correspondingly larger deflection in the lithosphere. Similarly to previous studies, back‐arc basins are deeper when mantle viscosity is higher. For a 50 km thick elastic lithosphere, the lithosphere‐asthenosphere interaction is negligible when the asthenospheric viscosity is less than 4 × 10 19  Pa s. Increasing the rate of subduction or decreasing the dip angle will also lead to the development of deeper basins.