Kinematic history of the Tanakura Shear Zone at brittle regime

  • Awaji Dohta
    Graduate School of Science and Engineering, Waseda University
  • Yamamoto Daisuke
    Department of Earth Sciences, School of Education, Waseda University Present address: Accenture Co., Ltd.
  • Takagi Hideo
    Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University

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Other Title
  • 棚倉破砕帯の脆性領域における運動履歴
  • タナクラ ハサイタイ ノ ゼイセイ リョウイキ ニ オケル ウンドウ リレキ

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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.<br>

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