K-Ar ages of phengite from the Kotsu and Iyo Besshi-type deposits in the Tokushima and Ehime Prefectures; Comparison with their Re-Os isochron ages

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  • NOZAKI Tatsuo
    Submarine Resources Research Center, Research Institute for Marine Resources Utilization, Japan Agency for Marine-Earth Science and Technology（ JAMSTECSubmarine Resources Research Center, Research and Technology (JAMSTEC) Frontier Research Center for Energy and Resources （FRCER）, Graduate School of Engineering, The University of Tokyo Department of Planetology, Graduate School of Science, Kobe University, 1-1 Ocean Resources Research Center for Next Generation, Chiba Institute of Technology
  • SATO Keiko
    Department of Applied Chemistry and Biochemistry, National Institute of Technology (Kosen), Fukushima College
  • KUMAGAI Hidenori
    Submarine Resources Research Center, Research Institute for Marine Resources Utilization, Japan Agency for Marine-Earth Science and Technology（ JAMSTECSubmarine Resources Research Center, Research and Technology (JAMSTEC)
  • SHIMADA Kazuhiko
    Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University
  • ISHIBASHI Jun-ichiro
    Kobe-Ocean Bottom Exploration Center （KOBEC）, Kobe University
  • KATO Yasuhiro
    Submarine Resources Research Center, Research Institute for Marine Resources Utilization, Japan Agency for Marine-Earth Science and Technology（ JAMSTECSubmarine Resources Research Center, Research and Technology (JAMSTEC) Frontier Research Center for Energy and Resources （FRCER）, Graduate School of Engineering, The University of Tokyo Ocean Resources Research Center for Next Generation, Chiba Institute of Technology Department of Systems Innovation, Graduate School of Engineering, The University of Tokyo

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Other Title
  • 徳島県高越および愛媛県伊予別子型鉱床のフェンジャイト K-Ar 年代：Re-Osアイソクロン年代との比較
  • トクシマケン コウエツ オヨビ エヒメケン イヨ ベッシガタ コウショウ ノ フェンジャイト K-Ar ネンダイ : Re-Os アイソクロン ネンダイ ト ノ ヒカク

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Abstract

<p>We determined the K-Ar ages of phengite occurring as a gangue silicate mineral in the massive sulfide ores from the Kotsu and Iyo Besshi-type volcanogenic massive sulfide (VMS) deposits in the Sanbagawa high-P/T metamorphic belt, southwest Japan. The K-Ar ages of phengite are dated to be ca. 45 or 85 Ma and these ages correspond to the timing of initial or terminal stages of regional retrograde metamorphism. Contrastingly, the Re-Os isochron ages of sulfide mineral aggregates from the Kotsu and Iyo Besshi-type VMS deposits are ca. 145 Ma, which is much older than those of phengite K-Ar ages. Since exactly the same ore samples were used for both K-Ar and Re-Os geochronology, it was confirmed that the K-Ar isotope system was reset due to the regional metamorphism up to lower epidote-amphibolite facies, although the Re-Os isotope system retained the original geochemical and isotopic composition even though the regional (Sanbagawa high-P/T) metamorphism. </p>

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  • Shigen-Chishitsu

    Shigen-Chishitsu 72 (1), 13-20, 2022-05-27

    The Society of Resource Geology

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