Hydration state of the incoming plate and updip fluid migration in the slab mantle

Fluid production from dehydration reactions and fluid migration in the subducting slab impact various subduction processes, including intraslab and megathrust earthquakes, episodic tremor and slip, mantle wedge metasomatism, and arc-magma genesis. To better understand these processes, it is crucial to determine the migration and the resulting distribution of fluids within the slab and along the slab surface.

A variety of geophysical observations and field studies suggest that intraslab updip fluid migration is plausible, yet quantitative numerical investigations of this process remain limited. So far, only models that incorporate compaction pressure gradients generated by fluids released during dehydration reactions have offered a convincing mechanism [1]. These models, however, are still not widely explored, and the influence of pre-subduction hydration of the oceanic mantle is particularly poorly constrained. In our study [2], 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 simulations indicate that prominent updip pathways develop along the segments of antigorite and chlorite breakdown fronts that run sub-parallel to the slab interface. The resulting updip fluid migration to depths as shallow as 30–40 km increases the volume of fluids that flux out across the slab surface at relatively shallow depths. Such behavior is most pronounced in young (< ~30 Ma), warm slabs, where the stability zones of hydrous phases in the incoming oceanic mantle are relatively thin (< ~20-km thick), enabling the development of the slab-parallel dehydration fronts that enhance updip flow.

 

[1] Wison et al., 2014, https://doi.org/10.1016/j.epsl.2014.05.052
[2] Cerpa & Wada, 2025, https://doi.org/10.1029/2024JB030609