Mantle serpentinization of subducting plate are controlled by combined effect of plate age and bending curvature

Abstract

A primary pathway for surface water to enter the Earth's interior is through faulting of oceanic plates. Mantle hydration of subducting plate is considered to play an important role on the water flux of subduction zone. Previous studies have found that the mantle hydration was related to plate bending and faulting, however the controlling mechanism of plate bending on mantle hydration at subduction zone is still highly unclear. In this study, we use the latest obtained reduction in uppermost mantle P-wave velocity (V_p) profiles beneath the subduction zone outer rise region, which is thought to be the result of mantle serpentinization, to examine the degrees of mantle serpentinization at several subduction zones and analyzed their relationship to plate age, bending curvature, and the sediment thickness near the trench. Results of analysis revealed that the average degree of the estimated mantle serpentinization increases with both the plate age and bending curvature, while it is hampered by sedimentation. The thick sediment can almost entirely prevent water from entering the mantle. Importantly, we found a good linear correlation between the reduction of uppermost mantle V_p and the theoretical brittle extensional strain determined by plate age and curvature. Based on this, a mechanism is proposed to illustrate the governing mechanism of the combined effect of the plate age and bending curvature in controlling the mantle serpentinization degree for global subduction zones.