Paleozoic submarine volcanoes in the high-P/T metamorphosed Chichibu system of Eastern Shikoku, Japan

Shigenori Maruyama, Masao Yamasaki

    Research output: Contribution to journalArticle

    13 Citations (Scopus)

    Abstract

    The Sawadani greenstone in the Chichibu Paleozoic System is an ancient submarine volcanic complex consisting of pillow lavas and hyaloclastites. The volcanism is divided into two periods. Alkali basalt was erupted in the first period and two shield-shaped cones were formed. After a period of dormancy the volcanism of the second period took place and a cone was formed by eruptions of lavas ranging in composition from mildly alkaline to tholeiitic basalt. The top of the volcano nearly reached the sea surface and was finally about 3.7 km above the base. A limestone cap and volcanic conglomerate were deposited on the summit. The base rests conformably on upper Carboniferous sandstone and subordinate mudstone derived from a continent or mature island arc. Many feeding channels of lava cut the volcanic body and underlying sedimentary formation. Sedimentation proceeded concurrently on the surrounding sea floor, so that volcanic and sedimentary material is interlayered. The Sawadani greenstone, although it occurs in the high-P/T metamorphic belt, is not believed to be a fragment of oceanic crust (ophiolite complex) formed by oceanic ridge volcanism and later carried into a convergent zone. It is a seamount formed on and within a sedimentary sequence near a continent or island arc. The magma changed from alkaline to tholeittic as the volcano grew. It cannot be assumed that all metavolcanic rocks formed in high-pressure metamorphic terranes are fragments of oceanic crust.

    Original languageEnglish
    Pages (from-to)199-216
    Number of pages18
    JournalJournal of Volcanology and Geothermal Research
    Volume4
    Issue number1-2
    DOIs
    Publication statusPublished - Aug 1978

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology

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