Effect of water solubilities on dehydration and hydration in subduction zones and water transport to the deep mantle: Implications for natural subduction zones

Role of warm subduction in the seismological properties of the forearc mantle: An example from southwest Japan

“…2D), most of the water finally reaches the overlying crust; only a small amount of free water is thus incorporated in the corner flow and leaves the model domain (Fig. 4) [e.g., (23,30)]. The isotropic permeability of the serpentinite layer (no foliated serpentinite) inhibits fluid flow toward the corner of the mantle wedge (see the Supplementary Materials).…”

“…The top depth transforms the base of the mantle wedge (chlorite-bearing lherzolite) above the fully coupled slab-mantle interface. The base is incorporated into the corner flow and gradually breaks down with depth [e.g., (23,30)]. Model results considering diverse subduction parameters and conditions show that the spontaneous growth of the serpentinite layer toward the corner of the mantle wedge can be observed only when we incorporate the anisotropic permeability of the serpentinite layer for the warm slab (see the Supplementary Materials).…”

“…For the boundary conditions of the solid-state flow, the slab-mantle decoupling zone on the slab surface is prescribed with 5% of the convergence rate for depths from 35 to 70 km, including the linear velocity ramp at a depth of 75 km, consistent with low heat flows of the forearc regions observed in southwest and northeast Japan (53). Below the downdip depth of the decoupling zone at a depth of 75 km, full coupling is applied to the slab surface [e.g., (23,30,54)]. No-slip and open boundary conditions are prescribed on the continental Moho and outer boundaries of the mantle wedge, respectively.…”

“…The solid flow of the mineral-bound water is governed by the solid-state flow of the subducting slab and mantle wedge, while the fluid flow of the free water is governed by the solid-state flow plus Darcy velocity driven by the density difference between the solid and free water. Using the small-porosity approximation and zerocompaction approximation (23,47), the mass conservation of the mineral-bound water and free water can be calculated by the following equations:…”

“…mass conservation of free water, where  and  are the mass and volume fractions of mineral-bound water and free water (•), V ⃑ s and V ⃑ f are the solid and free water velocities,  f ⟶ s and  s ⟶ f are the rates of mass transfer by hydration and dehydration,  s and  f are the solid and free water densities, and   and   are the artificial diffusivities of mineral-bound water and free water, respectively. The diffusion terms ∇ • (  ∇) and ∇ • (  ∇) are added to improve model stability [e.g., (23,30,47)].…”