十勝岳1988～89年本質噴出物とこれに伴うガラス質岩の岩石学 : 特集: 十勝岳1988～1989年噴火

DOI Web Site 被引用文献3件
  • 池田 保夫
    Department of Geology and Minraligy, Faculty of Science, Hokkaido University
  • 勝井 義雄
    Department of Geology and Minraligy, Faculty of Science, Hokkaido University
  • 中川 光弘
    Department of Geology and Minraligy, Faculty of Science, Hokkaido University
  • 河内 晋平
    Department of Geology and Minraligy, Faculty of Science, Hokkaido University
  • 渡辺 暉夫
    Department of Geology and Minraligy, Faculty of Science, Hokkaido University
  • 藤林 紀枝
    Department of Geology and Minraligy, Faculty of Science, Hokkaido University
  • 柴田 知之
    Institute for Study of the Earth's Interior, Okayama University
  • 加々美 寛雄
    Institute for Study of the Earth's Interior, Okayama University

書誌事項

タイトル別名
  • Petrology of the 1988-89 Essential Ejecta and Associated Glassy Rocks of Tokachi-dake Volcano in Central Hokkaido, Japan : Special Section: The 1988-1989 Eruption of Mt・ Tokachi, Central Hokkaido
  • 十勝岳1988～89年本質噴出物とこれに伴うガラス質岩の岩石学〔英文〕
  • トカチダケ 1988 89ネン ホンシツ フンシュツブツ ト コレ ニ トモナ

この論文をさがす

抄録

The 1988-89 explosive eruption of Tokachi-dake volcano brought about ash-and block-fall, pyroclastic surge, and small-scale pyroclastic flow deposit. Petrographical, mineralogical, and petrochemical studies were made on the essential ejecta of olivine-bearing orthopyroxene-clinopyroxene mafic andesite and asscciated glassy rocks of peculiar origin. The mafic andesites (SiO2=52-53 wt.%) have modal, mineralogical, petrochemical, and Sr isotope compositions similar to those of the 1962 mafic andesites of Tokachi-dake. However, the 1988-89 mafic andesites occur mainly as angular fragments which are less porous and possess more crystalline groundmasses than the 1962 mafic andesites. These observations suggest that the viscosity of the 1988-89 magma was higher than that of the 1962 magma. Mineral chemistries of the 1988-89 and 1962 mafic andesites display episodes of magma mixing. The glassy rocks occur as discrete fragments and are also found in ejected blocks of vent breccia. The glassy rocks are composed of deep brown glass, pale brown-colorless glass and dust, showing eutaxitic texture. The rocks also carry preserved clay and andesite shards. Areas which are gray frequently contain high-silica (SiO2=94%) pseudomorph after plagioclase displaying optical isotropy. The area-perimeter relationship for the deep brown glass is fractal, indicating the glass movement turned to be in a turbulent flow condition. Bulk chemistries of the glassy rocks have a wide compositional range (SiO2=61-7 9wt.%) and are similar to stoneware clay being extremely depleted in CaO and Na2O and enriched in Al2O3. The Sr isotopic data of the glassy rocks are similar to those of the associated andesites from Tokachi-dake volcano. Variations in Fe2O3-SiO2-Al2O3 compositions indicate that the glassy rocks are derived from an andesite suffered from alteration under strongly or weakly acidic condition. It is considered that the glassy rocks were derived from the melting or softening of an altered andesite around the vent. The above evidence suggests that low fluidity of the ascending mafic andesite and glassy product with a turbulent flow mode may have brought about the explosive nature of the 1988-89 eruption.

収録刊行物

  • 火山.第２集

    火山.第２集 35 (2), 147-162, 1990

    特定非営利活動法人 日本火山学会

被引用文献 (3)*注記

もっと見る

詳細情報 詳細情報について

問題の指摘

ページトップへ