Geometrical configuration, boundary conditions, and H
O transport of the model along the two-dimensional across-arc section. A constant subduction angle and the velocity of a straight slab are assumed. The boundary conditions for mass and energy transport are described in the main text. The thick (either solid or dashed) lines indicate the schematic transportation path of H2O that are predicted in this numerical model, with specific transport reaction events labeled <1> to <4> as follows: At <1>, the subducting oceanic crust dehydrates, and a part of the H2O within the oceanic crust is released upwards as aqueous fluid. At <2>, the ascending aqueous fluid hydrates the mantle wedge above the slab, and the hydrated mantle subducts along it. At <3>, the hydrated mantle dehydrates and forms an aqueous fluid column through which the fluid migrates upwards. At <4>, the ascending aqueous fluid lowers the solidus temperature to cause mantle melting.