The results of fluid-flow experiments revealed a significant permeability anisotropy in highly sheared serpentinite. Fluid flow parallel to serpentinite foliation is an order of magnitude or more higher than that normal to the foliation at confining pressures as high as ∼50 MPa. Although buoyancy is the driving force of upward fluid flow in the mantle, the strong anisotropy in permeability results in preferential fluid migration along the subducting plate interface, where extensive plastic deformation and a strong crystal-preferred orientation are expected to occur. The development of a relatively thin hydrous layer in the mantle wedge is consistent with the occurrence of highly anisotropic fluid migration rather than vertical flow.

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