In these models, the water density (1000 kg/m$^3$) is significantly lower than the solid density (3300 kg/m$^3$), so the fluid velocity is dominantly vertical due to the high buoyancy force experienced by the fluid. However, corner flow in the mantle wedge does impose a trench-ward horizontal component to the fluid velocity. As the fluid ascends through the hot peridotite mantle wedge, the PT conditions do not allow for the free fluid to be reabsorbed into the solid phase. However, when the free fluid starts ascending through the cooler overriding plate, the temperature is sufficiently low that hydration of the overriding plate begins to occur. This leads to a local reduction of the viscosity. Within the model where the fluid is advected with the Darcy velocity, two distinct bands of free water can be seen seeping out of the subducting plate. The first band produces a larger flux of water, is centered around a distance of ~175 km landward of the trench, and is sourced from the subducting peridotite layer. The second band is lower in flux magnitude, is centered around a distance of ~400 km landward from the trench, and is sourced from the gabbro and MORB layers.
0 commit comments