Olivine-spinifex basalt from the Tamba Belt, southwest Japan: Evidence for Fe- and high field strength element-rich ultramafic volcanism in Permian Ocean

Yuji Ichiyama, Akira Ishiwatari, Kazuto Koizumi, Yoshito Ishida, Sumiaki Machi

    研究成果: Article査読

    6 被引用数 (Scopus)

    抄録

    Permian basalt showing typical spinifex texture with >10 cm-long olivine pseudomorphs was discovered from the Jurassic Tamba accretionary complex in southwest Japan. The spinifex basalt occurs as a river boulder accompanied by many ferropicritic boulders in a Permian chert-greenstone unit. Groundmass of this rock is holocrystalline, suggesting a thick lava or sill for its provenance. Minor kaersutite in the groundmass indicates a hydrous magma. The spinifex basalt, in common with the associated ferropicritic rocks, is characterized by high high field strength element (HFSE) contents (e.g. Nb = 62 ppm and Zr = 254 ppm) and high-HFSE ratios (Al2O3/TiO 2 = 3.9, Nb/ Zr = 0.24 and Zr/Y = 6.4) unlike typical komatiites. The spinifex basalt and ferropicrite might represent the upper fractionated melt and the lower olivine-rich cumulate, respectively, of a single ultramafic sill (or lava) as reported from the early Proterozoic Pechenga Series in Kola Peninsula. Their parental magma might have been produced by hydrous melting of a mantle plume that was dosed with Fe- and HFSE-rich garnet pyroxenite. The spinifex basalt is an evidence for the Pechenga-type ferropicritic volcanism taken place in a Permian oceanic plateau, which accreted to the Asian continental margin as greenstone slices in Jurassic time.

    本文言語English
    ページ(範囲)493-503
    ページ数11
    ジャーナルIsland Arc
    16
    3
    DOI
    出版ステータスPublished - 2007 9月 1

    ASJC Scopus subject areas

    • 地球惑星科学(その他)

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