Granulite Facies Relics in the Early Paleozoic Kyanite-bearing Ultrabasic Metacumulate in the Oeyama Belt, the Inner Zone of Southwestern Japan

Tatsuki Tsujimori, Akira Ishiwatari

    Research output: Contribution to journalArticle

    7 Citations (Scopus)

    Abstract

    Granulite facies relics are found in the early Paleozoic kyanite-bearing melanocratic metagabbro from the Fuko Pass metacumulate mass of the Oeyama belt, southwestern Japan. The granulite facies assemblage consists of relict Al-rich clinopyroxene (up to 8.5 wt.% Al2O3) and pseudomorphs of spinel and plagioclase. The spinel pseudomorphs consist mainly of symplectic intergrowth of corundum and magnetite with minor gahnitic spinel. The plagioclase pseudomorphs are composed mainly of clinozoisite with minor kyanite. The symplectite suggests oxidation and Mg-depletion of the original spinel: hercynite (3FeAl2O4)+(O) = corundum (3Al2O3)+magnetite (Fe3O4). This oxidation reaction may have taken place at 700-900°C temperature. The melanocratic metagabbro has later been hydrated to form the epidote amphibolite assemblage represented by clinozoisite+kyanite+paragonite. The clinozoisite+kyanite assemblage has further reacted to form margarite at a lower temperature. The first granulite facies assemblage implies that the metacumulate has originally constituted a basal part of thick oceanic crust, and then has experienced the high-P/T type metamorphism in a subduction zone. This indicates that the thick oceanic crust has been formed and accreted to the Circum-Pacific orogenic belt in the early Paleozoic time.

    Original languageEnglish
    Pages (from-to)823-835
    Number of pages13
    JournalGondwana Research
    Volume5
    Issue number4
    DOIs
    Publication statusPublished - Oct 2002

    Keywords

    • Al-rich clinopyroxene
    • Corundum-magnetite intergrowth
    • Fuko Pass metacumulate
    • Lower crustal granulite
    • Oeyama belt

    ASJC Scopus subject areas

    • Geology

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