Process and geophysical implications of water migration in the plate subduction zone

Water (as hydrogen) plays an important role in geodynamics of our planet, not only because it enhances the diffusion and creep, but also because it lowers the melting temperature of the rock/mantle (i. e. , 'flux melting'). Furthermore, fluids significantly affect the geophysical properties of rock mass or the evolution of geological structures, even trigger geological disasters. Water-induced influence runs through the whole dynamic process of the plate subduction. However, the deep slab dehydration (at depth >300 km) is controversial, and the dynamic process of water migration in the subduction zone and its geophysical implications are still poorly understood. Two-dimensional chemical-thermal-mechanical coupling models, which used northeastern China as example, were implemented to simulate the slab subduction process, with particular attention paid to the whole continuous dynamics process of the fluid/water migration. The simulation and analysis results show that the process of water migration during plate subduction can be divided into three stages : ocean crust hydration, shallow (middle) slab dehydration, and deep slab dehydration. Furthermore, the mechanism of water seepage channel formation, water seepage and hydration reaction of plate and mantle material was revealed in the hydration process of ocean crust; the effects of shallow (middle) slab dehydration process on the formation of island arc, back-arc basin, low-velocity zone and the similar to 410 km discontinuity were explained; the phenomenon of deep slab dehydration was observed in the numerical simulation, which can explain the causes of some inland volcanoes as well as mantle plumes (magma plumes) and deep-source earthquakes in some areas. This study demonstrates the geophysical implications of water migration during plate subduction.