Abstract
The Tanakura Shear Zone is a NNW-SSE trending major fault which divides pre-Neogene basement rocks into NE and SW Japan. Within the study area, the fracture zone is 3 to 4 km in width, and consists of various kinds of fault rocks derived from the Jurassic accretionary complex of the Yamizo Belt, together with metamorphic and granitic rocks derived from the Abukuma Belt. Distribution patterns of brittle faults, fabric patterns and shear senses of fault gouge within the fault zone are described to interpret kinematics of the Tanakura Shear Zone during the Late Cenozoic. Based on paleo stress fields estimated from shear senses of fault gouge by multiple inverse methods (a technique to separate stresses based on heterogeneous fault-slip data), two brittle deformation stages (D1 and D2) are identified. During the Paleogene, a sinistral brittle fault set was originally generated. During exhumation of the shear zone, the fault kinematics inverted from a sinistral (D1 : 17 Ma) to a dextral movement (D2 : 15 Ma). Therefore, from Paleogene to the mid-Miocene, fault gouges within the Tanakura Shear Zone were reactivated under switched stress fields.
