Role of dynamic grain boundary wetting in fluid circulation beneath volcanic arcs

We report the influence of shear deformation on the microstructure of water-saturated olivine and clinopyroxene aggregates. Prior to deformation, the aqueous fluid was isolated in pockets along grain corners in the olivine-water aggregates, while it was interconnected by a network of grain-edge tubules in the clinopyroxene-water aggregate. During deformation of both types of aggregates, the aqueous fluid phase segregates into grain boundaries at an angle of similar to 16 degrees to the shear direction, inclined in a sense antithetic to the applied shear. Fluid-rich planes formed by such dynamic wetting of grain boundaries lead to the formation of high permeability paths in the matrix. In a deforming mantle, such high permeability paths will enhance the efficiency of aqueous fluid extraction from subducting slabs.