Geophysical implications of Izu-Bonin mantle wedge hydration from chemical geodynamic modeling

Using two-dimensional dynamic models of the Northern Izu-Bonin (NIB) subduction zone, we show that a particular localized low-viscosity (eta(LV) = 3.3 x 1019 - 4.0 x 1020 Pa s), low-density (Delta rho similar to -10 kg/m3 relative to ambient mantle) geometry within the wedge is required to match surface observations of topography, gravity, and geoid anomalies. The hydration structure resulting in this low-viscosity, low-density geometry develops due to fluid release into the wedge within a depth interval from 150 to 350 km and is consistent with results from coupled geochemical and geodynamic modeling of the NIB subduction system and from previous uncoupled models of the wedge beneath the Japan arcs. The source of the fluids can be either subducting lithospheric serpentinite or stable hydrous phases in the wedge such as serpentine or chlorite. On the basis of this modeling, predictions can be made as to the specific low-viscosity geometries associated with geophysical surface observables for other subduction zones based on regional subduction parameters such as subducting slab age.