北海道, 日高変成帯南部の角閃岩-ミグマタイト中の角閃岩の溶融現象とメルト溜りの形 Melting of amphibolites and the form of melt-trap in amphibolite-migmatites of the southern Hidaka metamorphic belt, Hokkaido, Japan

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グラニュライト相の変成度の異なる二つの角閃岩中において,部分溶融とメルトの分離が観察され,組織や鉱物の変化が記載された。部分溶融現象は振動的累帯構造をもつ自形斜長石の晶出で特徴的に示される。母岩基質に存在するレスタイト結晶や優白部の斜長石累帯構造より,部分溶融と結晶化は非平衡条件下で進行したものであることが示された。メルトは最初粒界に小さな斜長石—石英集合体として存在するが,メルトの量が増えると,メルトポケットやストロマティックなリュウコゾームを経て,脈に変化していく。母岩と脈岩の主成分と希土類元素組成が分析され,母岩と脈岩がレスタイトとメルトの関係にあることが示された。母岩と脈岩の主化学成分変化傾向は周囲の角閃石トーナル岩とは異なる。

Physical and chemical processes of partial melting and melt separation have been described based on the petrographical studies of amphibolite-migmatites of the Hidaka metamorphic belt. Melting texture is represented by the crystallization of idiomorphic plagioclase with oscillatory zoned structure. Amphibolites of zones D (low grade part of the granulite facies) and F (high grade part of the granulite facies) had melted and the melt had crystallized as leucosome. Meltpocket and stromatic leucosome are common in basic migmatites of zone D, and leucocratic crosscut veins are developed in zone F. Zone F amphibolites are higher in the volume percent of leucosome than zone D amphibolites, which indicates that the degree of melting of zone F amphibolites was larger than that of zone D amphibolites. Melting reactions took place in a state of disequilibrium, because the restitic plagioclases were heterogeneously dissolved in composition. Melt was trapped in the grain-boundary as a micro-network. As melt-volume had increased, a form of melt-reservoir changed from a chain of melt-pockets through stromatic leucosome to leucocratic vein in basic migmatites.<br>     Plagioclases which crystallized from melt have two types of zonal structure. One has a core of seed-crystal which was derived from a restitic plagioclase. The other has a complicated growth zoning which is due to the multi-stages of crystallization and a dissolution-texture. The plagioclase composition becomes sodic from core to rim in general. Melt composition had changed many times as often as trapped melts linked each together. Leucosome has experienced the crystallization-differentiation and the segregation of melt in the disequilibrium state.

収録刊行物

  • 岩鉱 : 岩石鉱物鉱床学会誌 : journal of mineralogy, petrology and economic geology  

    岩鉱 : 岩石鉱物鉱床学会誌 : journal of mineralogy, petrology and economic geology 90(2), 50-63, 1995-02-05 

    Japan Association of Mineralogical Sciences

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各種コード

  • NII論文ID(NAID)
    10002028975
  • NII書誌ID(NCID)
    AN10047992
  • 本文言語コード
    ENG
  • 資料種別
    ART
  • ISSN
    09149783
  • NDL 記事登録ID
    3610365
  • NDL 刊行物分類
    ME41(火山・岩石)
  • NDL 雑誌分類
    ZM46(科学技術--地球科学--岩石・鉱物・鉱床)
  • NDL 請求記号
    Z15-71
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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