阿蘇カルデラ西部に分布する栃ノ木溶岩中にみられる組成不均質とその成因

書誌事項

タイトル別名
  • Origin of compositional heterogeneity within Tochinoki andesitic lava flow from the western part of Aso caldera
  • アソ カルデラ セイブ ニ ブンプスル トチノキ ヨウガンチュウ ニ ミラレル ソセイ フキンシツ ト ソノ セイイン

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抄録

A composite lava flow is found in core samples of Tochinoki lava unit, one of the post-caldera volcanic products distributed in the western part of Aso caldera. Including core and surface outcrop samples, Tochinoki lava shows two compositionally different lava types. One is silicic (SiO2 63-66 wt%) and phenocryst-rich (8-16 vol%), and the other is mafic (SiO2 60-62 wt%) and phenocryst-poor (< 7 vol%). Mass balance calculation and trace element modeling show that the compositional variation found among Tochinoki core samples are explained by the fractional crystallization of plagioclase, clinopyroxene, orthopyroxene and magnetite phenocrysts from the most mafic lava. Tochinoki composite lava flow is probably produced by the viscous segregation of compositionally distinct magmas ascending simultaneously in the conduit as proposed by Inyo Obsidian Dome drilling project. Bulk rock composition and mineral chemistry indicate that mafic-silicic pairs observed in Tochinoki core samples are different from those in outcrop samples. This difference probably suggests the existence of contemporaneous multiple flow units in the Tochinoki lava unit.

収録刊行物

  • 岩石鉱物科学

    岩石鉱物科学 36 (1), 15-29, 2007

    一般社団法人 日本鉱物科学会

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