[S-CG54] 岩石―流体相互作用の新展開：表層から沈み込み帯深部まで

[SCG54-18] Fluid migration in the subducting slab and the mantle wedge in subduction zones

★Invited Papers

*Ikuko Wada¹、Nestor Cerpa² (1.University of Minnesota、2.Université de Montpellier)

キーワード：Fluid flow in subduction zones, 2-D two-phase flow models, Slab dehydration, Fluid viscosity

In this study, we aim to identify the major pathways of aqueous fluids within the subducting slab and through the overriding mantle wedge, using 2-D two-phase flow models that incorporate the effect of solid-matrix compaction. The development of fluid pathways in the subducting slab is influenced by the spatial distribution of fluid sources from slab dehydration, which depends on the initial hydration state and the thermal evolution of the subducting slab. Fluid pathways tend to develop along sites of dehydration, where fluid release generates compaction pressure gradients that drive fluid flow and elevated fluid fractions enhance permeability, facilitating fluid migration. The modeling results indicate that in relatively young and warm slabs, the dehydration of hydrous minerals in the slab mantle (e.g., antigorite and chlorite) occurs relatively close (<30 km slab-normal distance) to the slab surface. This results in the development of high-permeability channels sub-parallel to the slab surface, allowing fluid to travel updip within the slab mantle for tens of km before migrating towards the slab surface, thereby influencing the fluid distribution along the subduction interface. In contrast, in old and cold slabs, the development of similar high-permeability channels in the slab mantle is unlikely as it would require unreasonably thick initial hydration of the slab mantle, and updip fluid migration within the slab mantle would be limited. Previous modeling results indicate that the spatial variation in the viscosity of aqueous fluids influence the development of major fluid pathways in the mantle wedge (Cerpa et al., 2019). Because fluid viscosity depends strongly on silica content, we further explore its role by incorporating the empirically derived pressure and temperature (PT) dependence of silica solubility in aqueous fluids and the combined effects of PT and silica content on fluid viscosity.