Electrical Conductivity of Omphacite as a Function of Water Content and Implications for High Conductivity Anomalies in the Dabie-Sulu UHPM Belts and Tibet

Baohua Zhang, Chengcheng Zhao, Jianhua Ge, Takashi Yoshino

    Research output: Contribution to journalArticlepeer-review

    2 Citations (Scopus)

    Abstract

    Magnetotelluric surveys revealed high-conductivity layers in the lower crust beneath Tibet and in the shallow part of the upper mantle relevant to continental collision extending to the Dabie-Sulu ultrahigh-pressure metamorphic (UHPM) belts of eastern China, which have been interpreted by the presence of aqueous fluids/partial melts or hydrous phases. However, these explanations are not consistent with their petrological features and seismic properties. Hydrogen-bearing omphacite could be a probable candidate to explain such high-conductivity anomalies due to its high water-partitioning coefficient versus coexisting garnet in eclogite. In this study, we investigated electrical conductivities of Fe-free and Fe-bearing omphacite as a function of water content (0.005–0.122 wt.%) at 3 GPa and 500–1300 K. Our results show that water significantly enhances the electrical conductivity of omphacite, while iron facilitates conductivity by accelerating hydrogen diffusivity and lowering its activation enthalpy. Assuming a heat flow of 70 mW/m2, the high electrical anomalies observed beneath the Dabie-Sulu UHPM belts and the Tibetan Plateau can be reasonably explained by omphacite containing 0.07 wt.% water since water content higher than 0.07 wt.% in omphacite was frequently reported in naturally collected eclogite.

    Original languageEnglish
    Pages (from-to)12523-12536
    Number of pages14
    JournalJournal of Geophysical Research: Solid Earth
    Volume124
    Issue number12
    DOIs
    Publication statusPublished - Dec 1 2019

    Keywords

    • Dabie-Sulu UHPM belts
    • Tibet
    • electrical conductivity
    • high conductivity anomalies
    • omphacite
    • water

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology
    • Earth and Planetary Sciences (miscellaneous)
    • Space and Planetary Science

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