The effects of trivalent cations (Al and Fe) on the grain growth rates of bridgmanite

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Fei, Hongzhan ; Lyu, Yifu ; Wang, Fei ; McCammon, Catherine ; Katsura, Tomoo:
The effects of trivalent cations (Al and Fe) on the grain growth rates of bridgmanite.
In: Earth and Planetary Science Letters. Bd. 646 (2024) . - 118983.
ISSN 0012-821X
DOI: https://doi.org/10.1016/j.epsl.2024.118983

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Abstract

Trivalent cations such as Al3+ and Fe3+ can be incorporated into the crystal structure of bridgmanite either by the charge-coupled mechanism forming the FeFeO3, AlAlO3, and FeAlO3 components or by the oxygen vacancy mechanism forming the MgAlO2.5 and MgFeO2.5 components. They may affect the physical properties of bridgmanite and thus affect lower mantle dynamics. In this study, we investigated the effects of Al and Fe3+ on the grain growth kinetics of bridgmanite at a pressure of 27 GPa and temperatures of 2000 – 2300 K by multi anvil experiments. The experimental results indicate that the FeFeO3, AlAlO3, and FeAlO3 components enhance the growth rate of bridgmanite, while the MgAlO2.5 and MgFeO2.5 components have negligible effects. However, due to the relatively low Fe3+ and Al3+ contents of bridgmanite in the lower mantle, none of them affect the lower mantle rheology significantly. In particular, the mid-mantle viscosity jump interpreted from geoid analysis is unlikely to be caused by the decreasing of MgAlO2.5 and MgFeO2.5 concentrations with increasing depth.