Injection veins of crushing-originated pseudotachylyte and fault gouge formed during seismic faulting

Abstract

This paper describes the injection veins of crushing-originated pseudotachylate and fault gouge formed along the Iida-Matsukawa fault in granitic cataclasite, southern Nagano Prefecture, central Japan. The pseudotachylyte, which shows a dense and aphanitic appearances, and fault gouge occur as simple veins (fault vein) along the main fault plane and as complex network veins (injection vein) in the neighboring cataclasite. Locally, the injection veins of pseudotachylyte and fault gouge can be traced back to the fault veins. Powder X-ray diffraction patterns and petrological analysis indicate that both of the pseudotachylyte and fault gouge consist entirely of fine-grained angular clasts and that the pseudotachylytes and fault gouges have a similar X-ray diffraction patterns with that of the host granite. The similarity of chemical compositions and distribution patterns of grain size also show that the injection veins of pseudotachylyte and fault gouge have the same source material as that of fault veins. Field occurrences and petrological characteristics strongly suggest that the injection veins of pseudotachylyte and fault gouge formed during seismic faulting by a rapid intrusion and fluidization of crushed fine-grained materials generated in the shear zone in a gas-solid-fluid system.