Petrogenesis of greenstones from the Mino-Tamba belt, SW Japan: Evidence for an accreted Permian oceanic plateau

Yuji Ichiyama, Akira Ishiwatari, Kazuto Koizumi

    Research output: Contribution to journalArticlepeer-review

    46 Citations (Scopus)

    Abstract

    Permian greenstones in the Jurassic Mino-Tamba accretionary complex, southwest Japan, are divided into three distinct series on the basis of their geological occurrence, mineralogy, and geochemistry. A low-Ti series (LTS) is associated with Lower Permian chert and limestone, and is the most voluminous of the three series. The LTS shows slightly more enriched geochemical and isotopic characteristics than MORB. A transition series (TS) is mainly associated with Lower Permian chert, and has more enriched geochemical signatures than MORB. Its isotopic characteristics are divided into enriched and depleted types. A high-Ti series (HTS) occurs as sills and hyaloclastites within Middle Permian chert and as dikes intruding the TS. Some HTS rocks have high MgO contents. The HTS is characterized by enrichment in incompatible trace elements and an isotopic composition comparable to HIMU-type basalt. The geochemistry of the voluminous LTS is similar to that of the oceanic basalt series of the Kerguelen plateau, suggesting production by partial melting of a shallow mantle plume head below thick oceanic lithosphere in Early Permian time. We infer that the TS formed simultaneously at the margins of the mantle plume head. In contrast, the HTS may have resulted from partial melting of a deep mantle plume tail in Middle Permian time. Permian greenstones in the Mino-Tamba belt may have thus formed by superplume activity in an intra-oceanic setting. Given the presence of two known contemporary continental flood basalt provinces (Siberia and Emeishan) and some accreted oceanic plateau basalts, the vast magmatism of the Mino-Tamba oceanic plateau suggests a large-scale superplume pulse in Permian time. Accretion of oceanic plateaux may have played an important role in the growth of continental margins and island arcs in Japan and elsewhere in the circum-Pacific region.

    Original languageEnglish
    Pages (from-to)127-146
    Number of pages20
    JournalLithos
    Volume100
    Issue number1-4
    DOIs
    Publication statusPublished - 2008 Jan 1

    Keywords

    • Accretionary complex
    • Greenstone
    • Mino-Tamba belt
    • Oceanic plateau
    • Permian mantle plume

    ASJC Scopus subject areas

    • Geology
    • Geochemistry and Petrology

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