東北日本弧と大和海盆周辺のマグマの成因関係 : 「熱い指」のダイナミックモデル Genetic Relationship between Quaternary NE Japan Arc Magmas and Miocene Japan Sea Back-arc Basin Basalts : Implications for a Dynamic Model of Hot Fingers in the Mantle Wedge

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著者

    • 田村 芳彦 TAMURA Yoshihiko
    • 海洋科学技術センター固体地球統合フロンティア研究システム IFREE, JAMSTEC (Japan Marine Science and Technology Center)

抄録

Mantle melting and production of magmas in NE Japan may be controlled by locally developed hot regions within the mantle wedge that form inclined, 50 km-wide fingers. In this case, are these hot fingers chemically and/or isotopically different from the host mantle wedge? Forty-four Quaternary volcanoes in NE Japan have been reviewed to evaluate twodimensional strontium isotopic variations, and to infer <SUP>87</SUP>Sr/<SUP>86</SUP>Sr contours of the source mantle. The isotopic composition of magma source materials at depth is found to have little relationship with slab depth, suggesting that mantle heterogeneity was established before the flux of fluid released from the subducting slab reached the magma source regions. On the other hand, Miocene Japan Sea back-arc Yamato basin basalts have the same isotopic variation as the Quaternary volcanic arc. Cousens <I>et al</I>. (1994) suggested the possibility that partial melts of sediments, forming at a depth of >200 km may mix with mantle wedge material (<SUP>87</SUP>Sr/<SUP>86</SUP>Sr0.703), resulting in a magma source component with enriched <SUP>87</SUP>Sr/<SUP>86</SUP>Sr of0.705. I suggest that after the cessation of Yamato basin rifting, a MORB-like mantle source (<SUP>87</SUP>Sr/<SUP>86</SUP>Sr0.703) in the mantle wedge below the Quaternary NE Japan arc was replenished by a fertile mantle material (<SUP>87</SUP>Sr/<SUP>86</SUP>Sr0.705) through convection induced by the subducting lithosphere. On its way to the shallower mantle wedge (<150 km), the fertile mantle material changes shape from a hot sheet to hot fingers, for reasons not yet fully understood. Thus, the hot fingers, with <SUP>87</SUP>Sr/<SUP>86</SUP>Sr of0.705, extend from150 km below the back-arc region towards the shallower mantle (50 km) beneath the volcanic front. A conveyor-like return flow is interpreted to carry the remnants of these fingers to depth, resulting in greater amounts of fertile material being incorporated in diapirs beneath the volcanic front, and smaller amounts incorporated in areas behind the front.

収録刊行物

  • 地學雜誌

    地學雜誌 112(5), 781-793, 2003-10-25

    公益社団法人 東京地学協会

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各種コード

  • NII論文ID(NAID)
    10013950194
  • NII書誌ID(NCID)
    AN00322536
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    0022135X
  • NDL 記事登録ID
    6748626
  • NDL 雑誌分類
    ZM41(科学技術--地球科学)
  • NDL 請求記号
    Z15-169
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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