Water Concentration in Single‐Crystal (Al,Fe)‐Bearing Bridgmanite Grown From the Hydrous Melt: Implications for Dehydration Melting at the Topmost Lower Mantle

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  • Suyu Fu
    Department of Geological Sciences, Jackson School of Geosciences The University of Texas at Austin Austin TX USA
  • Jing Yang
    Department of Geological Sciences, Jackson School of Geosciences The University of Texas at Austin Austin TX USA
  • Shun‐ichiro Karato
    Department of Geology and Geophysics Yale University New Haven CT USA
  • Alexander Vasiliev
    National Research Center Kurchatov Institute Moscow Russia
  • Mikhail Yu. Presniakov
    National Research Center Kurchatov Institute Moscow Russia
  • Alexander G. Gavriliuk
    Shubnikov Institute of Crystallography of Federal Scientific Research Center Crystallography and Photonics Russian Academy of Sciences Moscow Russia
  • Anna G. Ivanova
    Shubnikov Institute of Crystallography of Federal Scientific Research Center Crystallography and Photonics Russian Academy of Sciences Moscow Russia
  • Erik H. Hauri
    Department of Terrestrial Magnetism Carnegie Institution of Washington Washington DC USA
  • Takuo Okuchi
    Institute for Planetary Materials Okayama University Misasa Japan
  • Narangoo Purevjav
    Institute for Planetary Materials Okayama University Misasa Japan
  • Jung‐Fu Lin
    Department of Geological Sciences, Jackson School of Geosciences The University of Texas at Austin Austin TX USA

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<jats:title>Abstract</jats:title><jats:p>High‐quality single‐crystals of (Al,Fe)‐bearing bridgmanite, Mg<jats:sub>0.88</jats:sub> Fe<jats:sup>3+</jats:sup><jats:sub>0.065</jats:sub>Fe<jats:sup>2+</jats:sup><jats:sub>0.035</jats:sub>Al<jats:sub>0.14</jats:sub>Si<jats:sub>0.90</jats:sub>O<jats:sub>3</jats:sub>, of hundreds of micrometer size were synthesized at 24 GPa and 1800 °C in a Kawai‐type apparatus from the starting hydrous melt containing ~6.7 wt% water. Analyses of synthesized bridgmanite using petrographic microscopy, scanning electron microscopy, and transmission electron microscopy show that the crystals are chemically homogeneous and inclusion free in micrometer‐ to nanometer‐spatial resolutions. Nanosecondary ion mass spectrometry (NanoSIMS) analyses on selected platelets show ~1,020(±70) ppm wt water (hydrogen). The high water concentration in the structure of bridgmanite was further confirmed using polarized and unpolarized Fourier‐transform infrared spectroscopy (FTIR) analyses with two pronounced OH‐stretching bands at ~3,230 and ~3,460 cm<jats:sup>−1</jats:sup>. Our results indicate that lower‐mantle bridgmanite can accommodate relatively high amount of water. Therefore, dehydration melting at the topmost lower mantle by downward flow of transition zone materials would require water content exceeding ~0.1 wt%.</jats:p>

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