Huang, R;
Boffa Ballaran, T;
McCammon, CA;
Miyajima, N;
Frost, DJ;
(2021)
The Effect of Fe-Al Substitution on the Crystal Structure of MgSiO3 Bridgmanite.
Journal of Geophysical Research-Solid Earth
, 126
(9)
, Article e2021JB021936. 10.1029/2021JB021936.
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Abstract
The crystal chemistry of ten well-characterized bridgmanite single-crystals with Fe and Al contents ranging from 0 to 0.40 atoms per two-cation formula units were investigated by single-crystal X-ray diffraction. Structural refinements indicate that Fe3+ and Al mainly occupy the Mg and Si sites, respectively, when present in similar proportions. Molar volumes of bridgmanite endmember components were refined using data from this and previous studies and found to decrease in the order Fe3+Fe3+O3 > MgFe3+O2.5 > Fe3+AlO3 > MgAlO2.5 > AlAlO3 > Fe2+SiO3 > MgSiO3. Fe3+AlO3 charge-coupled substitution leads to an anisotropic increase of B-O bond distances, resulting in more distorted octahedral B sites and in a more significant increase of the c-axis with respect to the a- and b-axes. Valence bond calculations indicate that the A site is more compressible than the B site for all bridgmanite samples studied, implying that octahedral tilting and distortion will dominate the bridgmanite compression mechanism. Guided by these crystal chemical observations, bulk moduli of bridgmanite endmember components were estimated using results of previous studies. The volume changes of equilibria controlling the speciation of bridgmanite components were then calculated at conditions relevant to the top of Earth's lower mantle. The proportion of oxygen vacancy components is predicted to decrease with pressure. While the stability of the bridgmanite Fe3+AlO3 component will drive charge disproportionation to produce iron metal at the top of the lower mantle, this appears to be much less favorable by 50 GPa. An increase in the proportion of the Fe3+Fe3+O3 bridgmanite component, however, may favor the formation of iron metal at higher pressures.
| Type: | Article |
|---|---|
| Title: | The Effect of Fe-Al Substitution on the Crystal Structure of MgSiO3 Bridgmanite |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1029/2021JB021936 |
| Publisher version: | https://doi.org/10.1029/2021JB021936 |
| Language: | English |
| Additional information: | This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | Science & Technology, Physical Sciences, Geochemistry & Geophysics, single-crystal X-ray diffraction, endmember molar volumes, ferric iron, octahedral tilting, lower mantle, EQUATION-OF-STATE, BOND-VALENCE PARAMETERS, PEROVSKITE-TYPE MGSIO3, LOWER-MANTLE, SILICATE PEROVSKITE, PHASE-TRANSFORMATIONS, FERRIC IRON, ELECTRICAL-CONDUCTIVITY, (MG,FE)SIO3 PEROVSKITE, ALUMINUM SUBSTITUTION |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10141051 |
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