100Ma hornblende K-Ar ages from Shimo-ondori adakitic granitoids, Naga, Tokushima, Outer Zone of Southwest Japan

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Other Title
  • 西南日本外帯，１００ＭａホルンブレンドＫ－Ａｒ年代を示す徳島県那賀町下雄アダカイト質花崗岩質岩

Description

Shimo-ondori adakitic granitoids intrude discordantly into the lower Cretaceous Akamatsu Formation, northern Shimanto Supergroup, Naga, Tokushima, outer zone of Southwest Japan. The granitoids consist of five small masses (5m x 15m) which were sporadically distributed. They were named A, B, C, D and E masses from east to west. The rocks, which contain mainly of hornblende and plagioclase, show wide chemical variation from high Mg andesite to adakite, but the minerals show restricted chemistries; mg values of hornblende range 0.65 to 0.81, those of salite, remnant in hornblende, range 0.75 to 0.82,and plagioclase shows albite composition. Three samples from B mass and one sample from E mass were selected for hornblende K-Ar age determination. 100 to 150 mesh size fraction from B-1 and 100 to 200 mesh fractions from B-3, B-5 and E-2 were determined at Hiruzen Institute for Geology and Chronology. The hornblende K-Ar ages from B mass yield 112.7+/-5.7, 129.6+/-6.4 and 131.4+/-6.6Ma, and the age from E-mass yields 94.3+/-4.7Ma. The result is too old to be the heat source for 14Ma granitoids in the outer zone of Southwest Japan.

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Details 詳細情報について

  • CRID
    1390282680521132160
  • NII Article ID
    130004601425
  • DOI
    10.14824/jakoka.2009.0.39.0
  • Text Lang
    ja
  • Data Source
    • JaLC
    • CiNii Articles
  • Abstract License Flag
    Disallowed

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