Incorporation of high amounts of Na in ringwoodite: Possible implications for transport of alkali into lower mantle

Luca Bindi*, Anastasia Tamarova, Andrey V. Bobrov, Ekaterina A. Sirotkina, Oliver Tschauner, Michael J. Walter, Tetsuo Irifune

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

8 Citations (Scopus)

Abstract

Here we report on the coexistence between Na-rich ringwoodite and bridgmanite in the system MgSiO3-Na2CO3-Al2O3 at 24 GPa and 1700 °C. In our experiments ringwoodite incorporates up to 4.4 wt% Na2O, with Na entering the octahedral site together with Si, according to the mechanism: Mg2+ → 2/3Na+ + 1/3Si4+. The volume of the unit cell increases along with the Na content. A similar behavior is observed for the unit-cell volume of Na-bearing bridgmanite, although the mechanism of Na incorporation into this structure remains unknown because of the lack of sufficient crystallographic data. Na2O is compatible in ringwoodite relative to bridgmanite with a partition coefficient (D) of 5 (+5/-4), but is incompatible in ringwoodite relative to carbonate-rich melt/fluid, with the D value ranging between 0.5 and 0.1. Al is highly enriched in bridgmanite relative to the other coexisting phases. Carbonatitic melt metasomatism in the deep transition zone may lead to local Na-enrichment, and ringwoodite may be an important host for Na in the deep transition zone. Subsequent convection or subduction of metasomatized mantle may lead to enrichment of alkaline elements in the upper and lower mantle.

Original languageEnglish
Pages (from-to)483-486
Number of pages4
JournalAmerican Mineralogist
Volume101
Issue number2
Early online date2 Feb 2016
DOIs
Publication statusPublished - Feb 2016

Keywords

  • alkalis
  • bridgmanite
  • crystal structure
  • microprobe analysis
  • sodium
  • spinel

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    Bindi, L., Tamarova, A., Bobrov, A. V., Sirotkina, E. A., Tschauner, O., Walter, M. J., & Irifune, T. (2016). Incorporation of high amounts of Na in ringwoodite: Possible implications for transport of alkali into lower mantle. American Mineralogist, 101(2), 483-486. https://doi.org/10.2138/am-2016-5570