Metamorphic evolution of kyanite-staurolite-bearing epidote-amphibolite from the Early Palaeozoic Oeyama belt, SW Japan

T. Tsujimori, J. G. Liou

    Research output: Contribution to journalArticle

    20 Citations (Scopus)

    Abstract

    Early Palaeozoic kyanite-staurolite-bearing epidote-amphibolites including foliated epidote-amphibolite (FEA), and nonfoliated leucocratic or melanocratic metagabbros (LMG, MMG), occur in the Fuko Pass metacumulate unit (FPM) of the Oeyama belt, SW Japan. Microtextural relationships and mineral chemistry define three metamorphic stages: relict granulite facies metamorphism (MI), high-P (HP) epidote-amphibolite facies metamorphism (M2), and retrogression (M3), MI is preserved as relict Al-rich diopside (up to 8.5 wt.% Al2O3) and pseudomorphs after spinel and plagioclase in the MMG, suggesting a medium-P granulite facies condition (0.8-1.3 GPa at > 850 °C). An unusually low-variance M2 assemblage, Hbl + Czo + Ky ± St + Pg + Rt ± Ab ± Crn, occurs in the matrix of all rock types. The presence of relict plagioclase inclusions in M2 kyanite associated with clinozoisite indicates a hydration reaction to form the kyanite-bearing M2 assemblage during cooling. The corundum-bearing phase equilibria constrain a qualitative metamorphic P-T condition of 1.1-1.9 GPa at 550-800 °C for M2. The M2 minerals were locally replaced by M3 margarite, paragonite, plagioclase and/or chlorite. The breakdown of M2 kyanite to produce the M3 assemblage at < 0.5 GPa and 450-500 °C suggests a greenschist facies overprint during decompression. The P-T evolution of the FPM may represent subduction of an oceanic plateau with a granulite facies lower crust and subsequent exhumation in a Pacific-type orogen.

    Original languageEnglish
    Pages (from-to)301-313
    Number of pages13
    JournalJournal of Metamorphic Geology
    Volume22
    Issue number4
    DOIs
    Publication statusPublished - May 1 2004

    Keywords

    • Early Palaeozoic
    • Epidote-amphibolite
    • Kyanite
    • P-T path
    • Polyphase metamorphism
    • Staurolite

    ASJC Scopus subject areas

    • Geology
    • Geochemistry and Petrology

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