Metamorphic age of the Otaki Group in the Mitsumine area of the Kanto Mountains, central Japan:

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  • Kato Daichi
    Department of Material Science, Okayama University of Science Present Address: Cyugoku Chika Kougyo Co., LTD.
  • Morimoto Ren
    Department of Applied Science, Okayama University of Science
  • Yagi Koshi
    Hiruzen Institute for Geology and Chronology Co., Ltd.
  • Aoki Shogo
    Graduate School of International Resource Sciences, Akita University Center for Fundamental Education, Okayama University of Science
  • Tsuchiya Yuta
    Center for Fundamental Education, Okayama University of Science
  • Aoki Kazumasa
    Center for Fundamental Education, Okayama University of Science

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Other Title
  • 関東山地三峰地域大滝層群の変成年代：
  • 関東山地三峰地域大滝層群の変成年代 : イライトK-Ar年代測定
  • カントウ サンチ ミツミネ チイキ オオタキソウグン ノ ヘンセイ ネンダイ : イライト K-Ar ネンダイ ソクテイ
  • illite K-Ar dating
  • イライトK-Ar年代測定

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Abstract

<p>Illite K-Ar dating was conducted on phyllites from the Futase and Kawamata units of the Otaki Group in the Mitsumine area, Kanto Mountains. The K-Ar ages from the eastern part of the Futase Unit are 60-51 Ma, which are younger than previously reported K-Ar ages of 76-65 Ma. The illite fractions yielded K-Ar ages of 48-44 Ma in the western part of the Futase Unit and 46-42 Ma in the Kawamata Unit. Compared with the previous study, the measurement fractions contain relatively high K contents, and there is no significant difference in the ages obtained for each part. These results lead to the suggestion that the previous K-Ar ages are apparently older due to the influence of detrital mica and quartz grains. Integration of our results with previously published data for metamorphism of the Otaki Group indicates that the new K-Ar ages reflect the timing of the metamorphic peaks for each part of the units.</p>

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