Compositional effects on element partitioning between Mg-silicate perovskite and silicate melts

Christian Liebske*, Alexandre Corgne, Daniel J. Frost, David C. Rubie, Bernard J. Wood

*Corresponding author for this work

    Research output: Contribution to journalArticle

    49 Citations (Scopus)

    Abstract

    High-pressure melting experiments were performed at ∼26 GPa and ∼2,200-2,400° C on synthetic peridotite compositions with varying FeO and Al2O3 contents and on a synthetic CI chondrite analogue composition. Peridotite liquids show a crystallisation sequence of ferropericlase (Fp) followed down temperature by Mg-silicate perovskite (MgPv) + Fp, which contrasts a sequence of MgPv followed by MgPv + Fp observed in the chondritic composition. The difference in crystallisation sequence is a consequence of the different bulk Mg/Si ratios. MgPv/melt partition coefficients for major, minor and trace elements were determined by electron microprobe and secondary ion mass spectrometry. Partition coefficients of tri- and tetravalent elements increase with increasing Al concentration in MgPv. A lattice strain model indicates that Al3+ substitutes predominantly onto the Si-site in MgPv, whereas most elements substitute onto the Mg-site, which is consistent with a charge-compensating coupled substitution mechanism. MgPv/melt partition coefficients for Mg (DMg) and Si (DSi) are related to the melt Mg/Si ratio such that DSi becomes lower than DMg at low Mg/Si melt ratios. We use a crystal fractionation model, based on upper mantle refractory lithophile element ratios, to constrain the amount of MgPv and Ca-silicate perovskite (CaPv) that could have fractionated during a Hadean magma ocean event and could still be present as a chemically distinct heterogeneity in the lower mantle today. We show that a fractionated crystal pile composed of 96% MgPv and 4% CaPv could comprise up to 13 wt% of the entire mantle.

    Original languageEnglish
    Pages (from-to)113-128
    Number of pages16
    JournalContributions to Mineralogy and Petrology
    Volume149
    Issue number1
    DOIs
    Publication statusPublished - Mar 2005

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