Permeability measurements and precipitation sealing of basalt in an ancient exhumed subduction-zone fault

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We conducted permeability measurements of basalt sampled from an exhumed ancient fault zone in the Cretaceous Shimanto accretionary complex in Japan, in order to investigate permeability structure and evolution following shear failure. Permeability showed a strong reduction with increase in the effective confining pressure and temperature. Rapid sealing at elevated temperatures was observed during hold experiments following shear failure. The results indicate that the permeability of a subduction megathrust fault would rapidly decrease due to the precipitation of clay-like minerals and other minerals, and indicates the potential for high fluid pressure in fault zones.