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Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solidification

Abstract : Thermochemical heterogeneities detected today in the Earth’s mantle could arise fromongoing partial melting in different mantle regions. A major open question, however, is thelevel of chemical stratification inherited from an early magma-ocean (MO) solidification.Here we show that the MO crystallized homogeneously in the deep mantle, but with che-mical fractionation at depths around 1000 km and in the upper mantle. Our arguments arebased on accurate measurements of the viscosity of melts with forsterite, enstatiteand diopside compositions up to ~30 GPa and more than 3000 K at synchrotron X-rayfacilities. Fractional solidification would induce the formation of a bridgmanite-enriched layerat ~1000 km depth. This layer may have resisted to mantle mixing by convection and causethe reported viscosity peak and anomalous dynamic impedance. On the other hand, fractionalsolidification in the upper mantle would have favored the formation of thefirst crust.
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https://hal.uca.fr/hal-02462106
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Longjian Xie, Akira Yoneda, Daisuke Yamazaki, Geeth Manthilake, Yuji Higo, et al.. Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solidification. Nature Communications, Nature Publishing Group, 2020, 11 (1), ⟨10.1038/s41467-019-14071-8⟩. ⟨hal-02462106⟩

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