青森県白神山地西部に発達する入良川マイロナイト帯の変形微細構造  [in Japanese] Deformation microstructures developed in the Iragawa mylonite zone in the western part of the Shirakami Mountains, Northeast Japan  [in Japanese]

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Author(s)

    • 綿貫 峻介 Watanuki Shunsuke
    • 早稲田大学大学院創造理工学研究科 地球・環境資源理工学専攻 Department of Earth Science and Environmental and Resources Engineering, Graduate School of Science and Engineering, Waseda University
    • 金井 拓人 Kanai Takuto
    • 早稲田大学大学院創造理工学研究科 地球・環境資源理工学専攻 Department of Earth Science and Environmental and Resources Engineering, Graduate School of Science and Engineering, Waseda University
    • 坂 秀憲 Saka Hidenori
    • 早稲田大学大学院創造理工学研究科 地球・環境資源理工学専攻|現所属:国立研究開発法人新エネルギー・産業技術総合開発機構 Department of Earth Science and Environmental and Resources Engineering, Graduate School of Science and Engineering, Waseda University|Present address: New Energy and Industrial Technology Development Organization
    • 高木 秀雄 Takagi Hideo
    • 早稲田大学教育・総合科学学術院地球科学教室 Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University

Abstract

<p>青森県白神山地の西部に分布する白神岳複合花崗岩質岩体には,海岸線に沿って,350m程度の幅を持ち南北約2.5kmにわたる延性剪断帯が発達しており,これを入良川マイロナイト帯と呼称する.中心部の幅200m程度の範囲はウルトラマイロナイト化しており,局所的にカタクレーサイト化を重複して受けている.マイロナイトの面構造は南北走向で東に40-80°傾斜し,線構造は北東方向に30-70°の沈下を示す.また,左横ずれ正断層の剪断センスを示す.再結晶石英の結晶方位と粒径を解析した結果,マイロナイト帯中心部では粒界すべりによる変形を,中心部以外では転位クリープによる変形を受けたと推定でき,変形時の環境は温度350-450°Cと推定される.その後,岩体が上昇し,300°C以下の環境で部分的に脆性破砕したという変形史が推定できる.</p>

<p>The Iragawa mylonite zone is ~2.5 km long (N-S) and ~350 m wide, and occurs in the Cretaceous Shirakamidake granitic complex along the western coastline of southernmost Aomori Prefecture, Northeast Japan. As already reported and confirmed by magnetic susceptibility measurements, the Iragawa mylonite zone is not the northern extension of the Hatagawa fault zone, but exists within the Abukuma Belt. The center of the mylonite zone, which is ~200 m wide, consists of ultramylonite locally overprinted by cataclasite. The mylonitic foliation strikes N-S and dips 40°-80° to the east, while the mylonitic lineation plunges at 30°-70° to the northeast. Asymmetric deformation microstructures indicate a sinistral normal shear. The lattice preferred orientation (LPO) and grain size of recrystallized quartz across the mylonite zone, as measured using SEM-EBSD, reveal that the most fine-grained ultramylonite displays a random LPO pattern and mean grain size of recrystallized quartz of 7.8-9.2 μm. The other mylonites mostly show LPO patterns indicating activity of the rhomb <<i>a</i>> and/or prism <<i>a</i>> systems, with a mean grain size of recrystallized quartz of 13-250 μm. The former suggests grain boundary sliding as the dominant deformation mechanism, whereas the latter suggests that dislocation creep took place at 350-450℃.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 123(7), 533-549, 2017

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130005893414
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    028446977
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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