The effects of mantle wedge serpentinization on slab dips

Abstract

The mechanical coupling between subducting slab and overlying mantle wedge is an important factor in controlling the dip angle of subduction and the flow in mantel wedge. In this paper, we investigate the role of the amount of mantle serpentinization on the evolution of the subduction zone. With numerical thermos-mechanical models with elasto-visco-plastic rheology, we vary the thickness and depth extent of mantle serpentinization in the mantle wedge to control the degree of coupling between the slab and the mantle wedge. A thin serpentinized mantle layer is required for stable subduction. For models with stable subduction, we find that the slab dip is affected by the down-dip extent and the thickness of mantle serpentinization. There exists a critical down-dip extent of mantle serpentinization, which is determined by the thickness of overriding lithosphere. If the down-dip extent does not exceed the critical depth, slab is partially coupled to the overriding lithosphere and has a constant dip angle regardless of mantle serpentinization thickness. However, if the down-dip extent exceeds the critical depth, the slab and the base of overriding lithosphere would be separated and decoupled by a thick layer of serpentinized peridotite. This allows further slab bending and results in steeper slab dip. Increasing mantle serpentinization thickness will also result in larger slab dip. We also find that with weak mantle wedge, there is no material flowing from asthenosphere into the serpentinized mantle wedge. All of these results indicates that serpentinization is an important ingredient when studying the subduction dynamics of in the mantle wedge.