ABSTRACT
Injection veins of pscudotachylyte and fault gouge are mainly composed of fine-grained crushed materials, can be linked to seismic faulting; good examples of this linkage occur in the Iida-Matsukawa fault, Nagano Prefecture, central Japan. The pseudotachylytes, which show 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. Powder X-ray diffraction patterns and petrological analysis indicate that both the pseudotachylyte and fault gouge consist entirely of fine-grained angular clasts and that those materials have similar X-ray diffraction patterns with those 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. Such injection veins, which are mainly composed of fine-grained crushed materials, are also found in the melting-originated and experimentally-generated pseudotachylyte veins. Field occurrences and petrological characteristics, therefore, strongly suggest that the injection veins of pseudotachylyte and fault gouge formed during seismic faulting by fluidization and rapid injection of fine-grained crushed materials generated in the shear zone in a gas-solidliquid system.
