The Middle Miocene Miyataki dike, central Kii Peninsula, southwest Japan: magma mingling observed in dike conduit and its implications

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  • Wada Yutaka
    Department of Earth Sciences, Nara University of Education
  • Fujita Chinatsu
    Department of Earth Sciences, Nara University of Education Present address; Heguri Minami Elementary School
  • Shinjoe Hironao
    Tokyo Keizai University

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  • 紀伊半島中央部，中期中新世宮滝岩脈：火道内でのマグマ・ミングリングとその意義
  • キイ ハントウ チュウオウブ チュウキ チュウシンセイ ミヤタキ ガンミャク カドウナイ デノ マグマ ミングリング ト ソノ イギ

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Abstract

We reexamined the Miocene Miyataki dike exposed at central Kii Peninsula, southwest Japan to infer the emplacement process of the dike. Although the dike has been regarded as of pyroclastic origin, our detailed field and petrographical investigations reveal that the Miyataki dike is composed of andesite mingled with rhyolite. In addition, granite enclaves also occur both in andesite and rhyolite, and those in rhyolite are often mantled by andesite. Shapes of rhyolite, andesite and granite enclaves are irregular and amoeboidal, indicative of ductile deformation during dike emplacement. These evidences show that andesite and rhyolite magmas and granite body could mingle with one another before dike emplacement, and that after the interaction, mingled magma rose to form the Miyataki dike. Whole rock compositions also support this mingling model for the Miyataki dike. Therefore, the facies and structures observed in the Miyataki dike are considered to be formed by a physical mingling processes in dike conduit.<br>

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