Metamorphism of the blueschists in the Suo metamorphic belt, Gotsu area, SW Japan

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  • LI Weimin
    College of Earth Science, Jilin University, China
  • KABIR Md Fazle
    Department of Geoscience, Graduate School of Science and Engineering, Shimane University
  • LIU Yongjiang
    College of Earth Science, Jilin University, China
  • GUO Xinzhuan
    College of Earth Science, Jilin University, China
  • TAKASU Akira
    Department of Geoscience, Graduate School of Science and Engineering, Shimane University San’in Branch, Earth Science Collaborative Research Association

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Other Title
  • 島根県江津地域周防変成帯 の青色片岩の変成作用

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Description

<p>There are two high-P/T type metamorphic belts distinguished as c. 300 Ma Renge belt and c.</p><p>200 Ma Suo belt in the Inner zone of SW Japan. In the Gotsu area of the Suo metamorphic belt, blueschists occur as lenses or layers intercalated in pelitic schists. The blueschists consist mainly of epidote, amphibole</p><p>(glaucophane, magnesioriebeckite, winchite, ferrowinchite, actinolite and magnesiohornblende) and chlorite, with minor amounts of phengite, albite, titanite, K-feldspar, biotite, calcite, apatite, hematite and quartz. A schistosity is defined by preferred orientation of amphibole, chlorite and epidote. Coarse-grained glaucophane- and epidote-rich layers are also developed along the schistosity. In the blueschists, three different metamorphic stages, i.e. prograde, peak and retrograde metamorphic stages, are distinguished on the basis of texture and compositional zoning of constituent minerals. The prograde stage is defined by inclusions in porphyroblastic epidote and amphibole, and core to mantle of matrix minerals, such as amphibole</p><p>(winchite and glaucophane), phengite (Si 6.45–6.9 pfu), chlorite, albite, epidote, hematite and titanite. These minerals suggest high-pressure greenschist facies to glaucophane schist facies. The peak metamorphic stage is well-defined by schistosity-forming minerals of epidote, glaucophanic amphibole (glaucophane, magnesioriebeckite), phengite (Si 6.9–7.1 pfu), chlorite and titanite. The peak mineral assemblage suggests the metamorphic conditions of epidote-blueschist facies at 380–540 °C and 1.1–1.4 GPa, which are likely to be the highest grade metamorphic conditions of the Suo belt. Magnesiohornblende/actinolite, chlorite and albite replacing the peak metamorphic minerals suggest the conditions of the greenschist facies at a retrograde metamorphic stage.</p>

Journal

  • Earth Science (Chikyu Kagaku)

    Earth Science (Chikyu Kagaku) 71 (1), 17-25, 2017-01-25

    The Association for the Geological Collaboration in Japan

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