Determination of the stress conditions of the ductile-to-brittle regime along the Asuke Shear Zone,SW Japan |
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| Institution: | 1. Department of Earth Sciences and Environmental and Resources Engineering, Graduate School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8050, Japan;2. Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University, Shinjuku, Tokyo 169-8050, Japan;1. Institute of Theoretical Physics, Hexi University, Zhangye 734000, China;2. School of Physics and Electromechanical Engineering, Hexi University, Zhangye 734000, China;3. Zhangye No. 1 Middle School, Zhangye 734000, China;4. Institute of Nuclear Physics and Chemistry, Chinese Academy of Engineering Physics, Mianyang 621900, China;1. Dipartimento di Scienze della Terra, Università di Napoli Federico II, Naples, Italy;2. Dipartimento di Scienze della Terra e dell''Ambiente, Università di Pavia, Via Ferrata, 1, Pavia, Italy;1. School of Physics and Technology, University of Jinan, Jinan 250022, China;2. School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China;3. Department of Physics, Jining University, Jining 273155, China;1. Department of Earth Sciences, Indian Institute of Science Education and Research Kolkata (IISERK), Mohanpur 741246, West Bengal, India;2. Department of Geology, Sonoma State University, 1801 E. Cotati Avenue, Rohnert Park, CA 94928, USA;2. Geoscience Department, Trinity University, One Trinity Place, San Antonio, TX 78212, USA;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;3. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;4. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;5. CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei 230026, China |
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| Abstract: | The stress conditions of the ductile-to-brittle regime have been assessed along the Asuke Shear Zone (ASZ), which strikes NE–SW in the Cretaceous Ryoke granite terrain in SW Japan. Along the ASZ, pseudotachylyte and mylonitized pseudotachylyte are locally developed together with cataclasite. The simultaneous operation of dislocation creep and grain-size-sensitive creep, as indicated by the coexistence of the Z-maximum and relatively random c-axis lattice preferred orientations as well as the sizes of dynamically recrystallized quartz grains (6.40–7.79 μm) in the mylonitized pseudotachylyte, suggest differential stresses of 110–130 MPa at ～300 °C. The e-twin morphology, twinning ratio, and distribution of the glide direction on the e-twin plane of the twinned calcite in the amygdules of the pseudotachylyte suggest the stress conditions of the σ1 and σ3 axes trend 228° and 320° and plunge 55° and 1°, respectively, and indicate differential stresses of 40–80 MPa at 150–200 °C. Based on kinematic indicators in the fault rocks, the stress conditions estimated from calcite twins, and the cooling history of the granitic protolith, the ASZ is inferred to have been activated under a stress state that caused sinistral normal movements before and after pseudotachylyte formation at 70–50 Ma. |
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| Keywords: | Ductile-to-brittle transition Mylonitized pseudotachylyte Asuke Shear Zone |
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