Trace element heterogeneity in hydrothermal diopside : evidence for Ti depletion and Sr-Eu-LREE enrichment during hydrothermal metamorphism of mantle harzburgite

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著者

    • PYTHON Marie
    • Faculty of Science, Department of Earth Science, Kanazawa University
    • ISHIDA Yoshito
    • Faculty of Science, Department of Earth Science, Kanazawa University
    • ARAI Shoji
    • Faculty of Science, Department of Earth Science, Kanazawa University

抄録

We discovered a new kind of dyke in the mantle section of the Oman ophiolite composed mainly of diopside that we called diopsidite, although traces of forsterite, anorthite, titanite or andradite may be also observed. The texture and chemical composition, and the relationship between antigorite and diopside or rare forsterite, suggest that they formed by high-T metamorphism of serpentine (antigorite) and are the result of interaction between hydrothermal fluid and percolating magma in the shallow mantle. Chemical data, obtained by electron microprobe and in situ laser ablation coupled to ICP-MS, show large heterogeneities from one sample to another and between diopside crystals in each sample. The trace element patterns are characterised by strong positive anomalies in Sr and Eu and a negative anomaly in Ti. Small-scale heterogeneities reflect the disequilibrium conditions in the dyke formation and show that a relatively Ti-rich- and Al-Eu-Sr-LREE-poor phase may be included in the diopside. The exact nature of this phase is difficult to determine but the Eu negative anomaly, and the low Sr and LREE concentration suggest that it is probably some partially altered, relict protolith mineral.

We discovered a new kind of dyke in the mantle section of the Oman ophiolite composed mainly of diopside that we called diopsidite, although traces of forsterite, anorthite, titanite or andradite may be also observed. The texture and chemical composition, and the relationship between antigorite and diopside or rare forsterite, suggest that they formed by high-<i>T</i> metamorphism of serpentine (antigorite) and are the result of interaction between hydrothermal fluid and percolating magma in the shallow mantle. Chemical data, obtained by electron microprobe and in situ laser ablation coupled to ICP-MS, show large heterogeneities from one sample to another and between diopside crystals in each sample. The trace element patterns are characterised by strong positive anomalies in Sr and Eu and a negative anomaly in Ti. Small-scale heterogeneities reflect the disequilibrium conditions in the dyke formation and show that a relatively Ti-rich- and Al-Eu-Sr-LREE-poor phase may be included in the diopside. The exact nature of this phase is difficult to determine but the Eu negative anomaly, and the low Sr and LREE concentration suggest that it is probably some partially altered, relict protolith mineral.

収録刊行物

  • Journal of mineralogical and petrological sciences  

    Journal of mineralogical and petrological sciences 102(2), 143-149, 2007-04-01 

    日本鉱物学会

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各種コード

  • NII論文ID(NAID)
    10018419219
  • NII書誌ID(NCID)
    AA11460926
  • 本文言語コード
    ENG
  • 資料種別
    SHO
  • ISSN
    13456296
  • データ提供元
    CJP書誌  CJP引用  IR  J-STAGE 
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