Abstract
Fluid production from dehydration reactions and fluid migration in the subducting slab impact various subduction processes, including intraslab and megathrust earthquakes, episodic slip and tremor, mantle wedge metasomatism, and arc-magma genesis. Quantifying those processes requires a good knowledge of the location and amount of fluid outflux at the top of the slab. Previous models of fluid migration indicate that compaction-pressure gradients induced by the dehydration reactions could drive updip intraslab fluid flow (Wilson et al., 2014). However, how the initial hydration in the oceanic mantle prior to subduction impacts the updip fluid flow has not been investigated. Here, we use a 2-D two-phase flow model to investigate this effect under various initial slab-mantle hydration states and slab thermal conditions, both of which impact the depth extent of the stability of hydrous minerals. We focus on the lateral shift between the site of dehydration reactions and the location of fluid outflux at the top of the slab due to intraslab-updip migration. Our results indicate that major updip fluid pathways form along the antigorite and chlorite dehydration fronts sub-parallel to the slab surface. This, in turn, promotes slab-fluid outflux at the slab surface as shallow as 30–40 km depths. This mechanism is more likely in young slabs (< ~30 Ma), in which the thickness of the hydrated mantle in the incoming oceanic mantle that is required to form the slab-parallel dehydration fronts is relatively small (< ~20 km) because of its warm condition and thus a relatively thin antigorite stability zone.