隠岐島後,隠岐粗面岩・流紋岩類のRb-Sr全岩アイソクロン年代と成因

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タイトル別名
  • The Rb-Sr Whole Rock Isochron Age and Genesis of Oki Trachyte-rhyolite Group in Oki Dogo Island
  • オキ ドウゴ オキ ソメンガン リュウモンガンルイ ノ Rb Sr ゼンガン

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The precise age for the Oki trachyte-rhyolite group was determined by Rb-Sr whole rock isochron method. This trachyte-rhyolite group was formed by a large scale ring fissured eruption on the Oki Dogo Island in the Japan Sea. A regression of the Rb-Sr isotopic data yields an age of 6.8±0.2 Ma with an initial Sr isotopic ratio (Sri) of 0.707176±0.000080 (2a). This age is consistent with the K-Ar age of 6.3 Ma determined by KANEOKA (1970), and is similar to the activity ages of alkali basalts occurring in Oki Dozen Islands near the Oki Dogo Island. The fission track age of 3.6 Ma by SUZUKI (1970) may be caused by some late annealing events. The Sri determined for the Oki trachyte-rhyolite group is very close to that of basic granulite xenoliths included in some alkali basalts. The lower crust beneath the Oki Dogo Island is considered to be composed of these basic granulites which are very poor in alkali metals. It is proposed that the magma of the Oki trachyte-rhyolite group was formed by partial melting of the lower crust with leaving the basic granulite as a residue.

収録刊行物

  • 火山.第２集

    火山.第２集 33 (2), 79-86, 1988

    特定非営利活動法人 日本火山学会

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