Constraining the timing of brittle deformation and faulting in the Toki granite, central Japan

Constraining of the timing of fault zone formation is of fundamental geotectonic importance to understand structural evolution and brittle fault processes. Here, we present authigenic illite K-Ar age data from brittle fault zones comprising two gouges within the Toki granite, central Japan. The gouge samples were collected at depths of 252.9 and 403.7. m from a shaft at the Mizunami Underground Research Laboratory, and were separated into five grain-size fractions (