マグマ/かんらん岩相互反応の結果としてのポディフォーム・クロミタイト形成における壁岩組成コントロール Control of Wall-rock Composition on the Formation of Podiform Chromitites as a Result of Magma/Peridotite Interaction

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Podiform chromitites with dunitic envelopes, especially undeformed ones, usually cut mantle peridotite as dikes or pipes. Large-scale chromitites are usually set within the moderately refractory peridotite; i.e., the harzburgite with chromian spinel of intermediate Cr# (=Cr/[Cr+Al] atomic ratio), 0.4 to 0.6. Podiform chromitites are usually absent or very small in volume, in both fertile lherzolite and highly refractory harzburgite. This relationship indicates that the wall-rock chemistry controls to some extent the formation of chromitites, and is concordant with a petrogenetic model whereby podiform chromitite is formed by reaction between upwelling melt and mantle peridotite protolith and related melt mixing. Both the Cr# and the total amount of (Al+Cr) in the involved system, especially of orthopyroxene of the protolith, control the size and chemistry of the podiform chromitite, a reaction product. For fertile lherzolite wall, the Cr# of the system is too low to concentrate spinel because the mixed melt is relatively low in the degree of spinel-oversaturation. For highly refractory harzburgite wall, the amount of (Al+Cr) of the system is too low to precipitate large amounts of spinel. The moderately refractory harzburgite is satisfactory for the two criteria, and can be a host for large-scale podiform chromitites. Upper mantle beneath arc, especially arc proper and back-arc basin, and fast-spreading oceanic ridges is suitable for the podiform chromitite formation because the harzburgite with chromian spinel of intermediate Cr# is available there. Both melt/peridotite interaction and magma mixing can occur to precipitate large amount of chromian spinel at the Moho transition zone where upwelling melt is pooled within the harzburgite mantle.

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  • 資源地質  

    資源地質 47(4), 177-187, 1997-08-30 

    The Society of Resource Geology

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各種コード

  • NII論文ID(NAID)
    10002859667
  • NII書誌ID(NCID)
    AN10379890
  • 本文言語コード
    ENG
  • 資料種別
    ART
  • ISSN
    09182454
  • NDL 記事登録ID
    4322543
  • NDL 雑誌分類
    ZM49(科学技術--地球科学--地質) // ZM46(科学技術--地球科学--岩石・鉱物・鉱床)
  • NDL 請求記号
    Z15-123
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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