Experimental and theoretical study of stability of dense hydrous magnesium silicates in the deep upper mantle

Tetsuya Komabayashi, Soichi Omori, Shigenori Maruyama

    Research output: Contribution to journalArticle

    39 Citations (Scopus)

    Abstract

    Fluid-undersaturated experiments were conducted to determine the phase relations in the simplified peridotite system MgO-SiO2- H2O (MSH) at 11.0-14.5 GPa and 800-1400 °C. Stability relations of dense hydrous magnesium silicates (DHMSs) under fluid-undersaturated conditions were experimentally examined. From the fluid-absent experimental results, we retrieved thermodynamic data for clinohumite, phase A, phase E, and hydrous wadsleyite, consistent with the published data set for dry mantle minerals. With this new data set, we have calculated phase equilibria in the MSH system including dehydration reactions. The dehydration reactions calculated with lower water activities of 0.68-0.60 match the fluid-present experiments of this study above 11.0 GPa and 1000 °C, indicating that considerable amounts of silicate component were dissolved into the fluid phase. The calculated phase equilibria illustrate the stability of the post-antigorite phase A-bearing assemblages. In the cold subducting slab peridotite, phase A + enstatite assemblage survives into the transition zone, whereas phase A + forsterite + enstatite assemblage forms hydrous wadsleyite at a much shallower depth of about 360-km. The slab is subducted with no dehydration reactions occurring when entering the transition zone. The phase equilibria also show the high temperature stability of phase E. Phase E is stable up to 1200 °C at 13.5 GPa, a plausible condition in the mantle of relatively low temperature, i.e., beneath subduction zones. Phase E is a possible water reservoir in the mantle as well as wadsleyite and ringwoodite.

    Original languageEnglish
    Pages (from-to)191-209
    Number of pages19
    JournalPhysics of the Earth and Planetary Interiors
    Volume153
    Issue number4
    DOIs
    Publication statusPublished - Dec 15 2005

    Keywords

    • High pressure
    • Hydrous phase
    • Subduction
    • Thermodynamic data
    • Water transportation

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Geophysics
    • Physics and Astronomy (miscellaneous)
    • Space and Planetary Science

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