The formation environment of Allende CAIs inferred from their size and chemical composition

  • HAYASHI Masato
    Department of Earth and Planetary Sciences, School of Science, Nagoya University
  • TANAKA Tsuyoshi
    Department of Earth and Planetary Sciences, School of Science, Nagoya University
  • KAMIOKA Hikari
    Geochemistry Department, Geological survey of Japan

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  • アレンデ隕石中のCAIの大きさと化学組成からみたCAIの生成場について
  • アレンデ インセキチュウノ CAI ノ オオキサ ト カガク ソセイ カラ ミ

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Trace element abundances were determined by INAA for forty-nine inclusions of various sizes in the Allende meteorite, especially medium-to-small-sized inclusions were emphasized to analyze. All of the refractory elements in coarse grained inclusions analyzed in the present study were enriched by a factor of only eight relative to their concentrations in Cl chondrites though in the previous studies enriched by a factor of twenty. The concentrations of refractory elements in the coarse grained inclusions, the amoeboid olivine aggregates and magnetite rich inclusions correlate positively to the sizes of inclusions. This suggests that these inclusions suffered secondary alteration and the refractory elements were diluted. As the refractory elements in the coarse grained inclusions were more enriched than in the amoeboid olivine aggregates, the coarse grained inclusions are considered to have been removed from equilibrium with the gas before the amoeboid olivine aggregates removed. On the other hand, the abundances of refractory elements in the fine grained inclusions were nearly identical with those reported in the earlier works, irrespective of the size; the light REEs are enriched by a factor of twenty and heavy REEs enriched by less than three. This suggests that the fine grained inclusions suffered no alteration. Some possible models for the formation mechanism of CAI were discussed in the light of the size and chemical composition. It has been made clear that the difference between coarse and fine grained inclusion is not only their appearance but also their fomation environment.


  • Chikyukagaku

    Chikyukagaku 29 (1), 37-50, 1995

    The Geochemical Society of Japan


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