Stability and Solubility of the FeAlO<sub>3</sub> Component in Bridgmanite at Uppermost Lower Mantle Conditions

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  • Zhaodong Liu
    Bayerisches Geoinstitut University of Bayreuth Bayreuth Germany
  • Catherine McCammon
    Bayerisches Geoinstitut University of Bayreuth Bayreuth Germany
  • Biao Wang
    Bayerisches Geoinstitut University of Bayreuth Bayreuth Germany
  • Leonid Dubrovinsky
    Bayerisches Geoinstitut University of Bayreuth Bayreuth Germany
  • Takayuki Ishii
    Bayerisches Geoinstitut University of Bayreuth Bayreuth Germany
  • Dmitry Bondar
    Bayerisches Geoinstitut University of Bayreuth Bayreuth Germany
  • Ayano Nakajima
    Department of Earth Sciences, Graduate School of Science Tohoku University Sendai Japan
  • Yoshinori Tange
    SPring‐8 Japan Synchrotron Radiation Institute Hyogo Japan
  • Yuji Higo
    SPring‐8 Japan Synchrotron Radiation Institute Hyogo Japan
  • Tian Cui
    State Key Laboratory of Superhard Materials Jilin University Changchun China
  • Bingbing Liu
    State Key Laboratory of Superhard Materials Jilin University Changchun China
  • Tomoo Katsura
    Bayerisches Geoinstitut University of Bayreuth Bayreuth Germany

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<jats:title>Abstract</jats:title><jats:p>We report the stability and solubility of the FeAlO<jats:sub>3</jats:sub> component in bridgmanite based on phase relations in the system MgSiO<jats:sub>3</jats:sub>‐FeAlO<jats:sub>3</jats:sub> at 27 GPa and 2000 K using a multi‐anvil apparatus combined with in situ synchrotron X‐ray diffraction measurements. The results demonstrate that the FeAlO<jats:sub>3</jats:sub> component dominates Fe<jats:sup>3+</jats:sup> and Al<jats:sup>3+</jats:sup> substitution in bridgmanite, although trace amounts of oxygen‐ and Mg‐site vacancy components are also present. Bridgmanite with more than 40 mol% FeAlO<jats:sub>3</jats:sub> transforms into the LiNbO<jats:sub>3</jats:sub>‐type phase upon decompression. The FeAlO<jats:sub>3</jats:sub> end‐member decomposes into corundum and hematite and does not form single‐phase bridgmanite. We determined the maximum solubility of the FeAlO<jats:sub>3</jats:sub> component in bridgmanite at 27 GPa and 2000 K to be 67 mol%, which is significantly higher than previously reported values (25–36 mol%). We determined the partial molar volume (27.9 mol/cm<jats:sup>3</jats:sup>) and bulk modulus (197 GPa) of hypothetical FeAlO<jats:sub>3</jats:sub> bridgmanite, which are significantly higher and lower than those of AlAlO<jats:sub>3</jats:sub> and FeSiO<jats:sub>3</jats:sub> bridgmanite, respectively. The non‐ideality of MgSiO<jats:sub>3</jats:sub>‐FeAlO<jats:sub>3</jats:sub> solid solution (<jats:italic>W</jats:italic> = 13 kJ/mol, where <jats:italic>W</jats:italic> is the interaction parameter) is significantly larger than that for MgSiO<jats:sub>3</jats:sub>‐AlAlO<jats:sub>3</jats:sub> (5 kJ/mol) and MgSiO<jats:sub>3</jats:sub>‐FeSiO<jats:sub>3</jats:sub> (3 kJ/mol) solid solutions. The rapid decrease in abundance of the MgAlO<jats:sub>2.5</jats:sub> component in bridgmanite with increasing pressure is enhanced by the presence of the FeAlO<jats:sub>3</jats:sub> component. The FeAlO<jats:sub>3</jats:sub> content in pyrolite and mid‐ocean ridge basalt is far below its solubility limit in bridgmanite and provides new insight into the mineralogy of the lower mantle.</jats:p>

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