日本海竹島海山(仮称)のかんらん岩捕獲岩の成因とその意義 Peridotite xenoliths from the Takeshima seamount, Japan : an insight into the upper mantle beneath the Sea of Japan

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著者

    • 二ノ宮 小満 NINOMIYA Chima
    • 金沢大学大学院自然科学研究科地球学教室 Department of Earth Sciences, Graduate School of Natural Science and Technology, Kanazawa University
    • 荒井 章司 ARAI Shoji
    • 金沢大学大学院自然科学研究科地球学教室 Department of Earth Sciences, Graduate School of Natural Science and Technology, Kanazawa University

抄録

The Sea of Japan is one of the back-arc basins distributed around the western rim of the Pacific. Nature of the plume for back-arc basin (= BAB) opening is unknown partly because petrological characteristics of the BAB mantle are not well known compared with mid-ocean ridge (= MOR) mantle. Peridotite xenoliths in an alkali basalt dredged from the Takeshima seamount (tentative name), ca. 230 km to the north of Oki islands, are examined to clarify the petrological feature of the Japan-Sea mantle. They are spinel-bearing lherzolite to harzburgite with equigranular to porphyroclastic textures. They can be classified into two types (Type 1 and Type 2 peridotites) in terms of REE (= rare earth elements) patterns of clinopyroxene (= cpx). Type 1 peridotites (Cr# of spinels, 0.4-0.5) are similar to abyssal peridotites in terms of major element chemistry and middle- to heavy-REE concentrations of cpx. The cpx in the former shows slight enrichment of LREE (= light REE), which is apparently due to metasomatism by slab-derived fluids/melts. Type 2 peridotites have high-REE cpx with flat to slightly LREE-enriched patterns, and are quite similar to subcontinental peridotites obtained as xenoliths from China. The southern part of the Sea of Japan was formed by mainly thinning and rifting of the continental lithosphere. Type 2 peridotites are a remnant of the continental lithospheric mantle. Chemical characteristics of BAB basalts and Type 1 peridotites indicate that open-system melting of peridotite affected by a flux from the downgoing slab was involved in the Japan-Sea opening.

The Sea of Japan is one of the back-arc basins distributed around the western rim of the Pacific. Nature of the plume for back-arc basin (= BAB) opening is unknown partly because petrological characteristics of the BAB mantle are not well known compared with mid-ocean ridge (= MOR) mantle.<br>     Peridotite xenoliths in an alkali basalt dredged from the Takeshima seamount (tentative name), <i>ca</i>. 230 km to the north of Oki islands, are examined to clarify the petrological feature of the Japan-Sea mantle. They are spinel-bearing lherzolite to harzburgite with equigranular to porphyroclastic textures. They can be classified into two types (Type 1 and Type 2 peridotites) in terms of REE (= rare earth elements) patterns of clinopyroxene (= cpx). Type 1 peridotites (Cr# of spinels, 0.4-0.5) are similar to abyssal peridotites in terms of major element chemistry and middle- to heavy-REE concentrations of cpx. The cpx in the former shows slight enrichment of LREE (= light REE), which is apparently due to metasomatism by slab-derived fluids/melts. Type 2 peridotites have high-REE cpx with flat to slightly LREE-enriched patterns, and are quite similar to subcontinental peridotites obtained as xenoliths from China. The southern part of the Sea of Japan was formed by mainly thinning and rifting of the continental lithosphere. Type 2 peridotites are a remnant of the continental lithospheric mantle.<br>     Chemical characteristics of BAB basalts and Type 1 peridotites indicate that open-system melting of peridotite affected by a flux from the downgoing slab was involved in the Japan-Sea opening.

収録刊行物

  • 岩石鉱物科学

    岩石鉱物科学 36(1), 1-14, 2007-01-30

    Japan Association of Mineralogical Sciences = 日本鉱物科学会

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各種コード

  • NII論文ID(NAID)
    10018411339
  • NII書誌ID(NCID)
    AA1146088X
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    1345630X
  • NDL 記事登録ID
    8757463
  • NDL 雑誌分類
    ZM46(科学技術--地球科学--岩石・鉱物・鉱床)
  • NDL 請求記号
    Z15-117
  • データ提供元
    CJP書誌  NDL  IR  J-STAGE 
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