The subduction zone water cycle revisited with novel 2D and 3D numerical models

The subduction zone water cycle, i.e. the hydration and dehydration of subducting oceanic lithosphere, is a key process in understanding arc magmatism and volatile recycling processes. Hydration of oceanic crust begins at mid-ocean ridges through hydrothermal alteration and continues more slowly as the seafloor ages. Finally, there is now robust evidence that bend-faulting at the outer rise leads to serpentinization of the cold lithospheric mantle. Dehydration occurs deeper within the subduction zone by fluid releasing metamorphic reactions. These rising fluids flux the mantle wedge where they trigger arc melting. Adiabatic mantle decompression, which requires an upward velocity component in the solid-state mantle flow, may \nalso contribute to sub-arc melt generation. \nThis study uses two- and three-dimensional numerical models to explore plate hydration at the outer rise and consequences of plate dehydration for mantle wedge dynamics. Hydration reactions are simulated with a 2D reaction transport model that resolves for seawater circulation as well as serpentinization. We find that bend-faults are likely to be highly serpentinized. \nBackground serpentinization is most intense around the 270°C isotherm where the reaction rate is at its maximum. 3D mantle flow calculations are used to elucidate mantle wedge dynamics. Here we find that threedimensional diapiric upwellings, fueled by buoyant slab fluids, dominant the \nmantle wedge flow for a wide parameter range. These calculations clearly show that findings and intuition built upon 2D pictures will need to be revised as high resolution simulations become more feasible with the development of \nnew codes and the availability of better hardware.