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

Abstract

In this study, we report on the coexistence between Na-rich ringwoodite and bridgmanite in the system MgSiO 3-Na 2CO 3-Al 2O 3 at 24 GPa and 1700 °C. In our experiments ringwoodite incorporates up to 4.4 wt% Na 2O, with Na entering the octahedral site together with Si, according to the mechanism: Mg 2+ → 2/3Na + + 1/3Si 4+. 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. Na 2O 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.

Authors:
 [1];  [2];  [3];  [3];  [4];  [5];  [6]
  1. Univ. di Firenze, Firenze (Italy); CNR - Istituto di Geoscienze e Georisorse, Firenze (Italy)
  2. Moscow State Univ., Moscow (Russian Federation)
  3. Moscow State Univ., Moscow (Russian Federation); Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Moscow (Russia)
  4. Univ. of Nevada, Las Vegas, NV (United States)
  5. Univ. of Bristol, Bristol (United Kingdom)
  6. Ehime Univ., Matsyama (Japan); Tokyo Institute of Technology, Tokyo (Japan)
Publication Date:
Research Org.:
Univ. of Nevada, Las Vegas, NV (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1332403
Grant/Contract Number:  
NA0001982
Resource Type:
Accepted Manuscript
Journal Name:
American Mineralogist
Additional Journal Information:
Journal Volume: 101; Journal Issue: 2; Journal ID: ISSN 0003-004X
Publisher:
Mineralogical Society of America
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Ringwoodite; bridgmanite; sodium; spinel; crystal structure; microprobe analysis; alkalis

Citation Formats

Bindi, Luca, Tamarova, Anastasia, Bobrov, Andrey V., Sirotkina, Ekaterina A., Tschauner, Oliver, Walter, Michael J., and Irifune, Tetsuo. Incorporation of high amounts of Na in ringwoodite: Possible implications for transport of alkali into lower mantle. United States: N. p., 2016. Web. doi:10.2138/am-2016-5570.
Bindi, Luca, Tamarova, Anastasia, Bobrov, Andrey V., Sirotkina, Ekaterina A., Tschauner, Oliver, Walter, Michael J., & Irifune, Tetsuo. Incorporation of high amounts of Na in ringwoodite: Possible implications for transport of alkali into lower mantle. United States. doi:10.2138/am-2016-5570.
Bindi, Luca, Tamarova, Anastasia, Bobrov, Andrey V., Sirotkina, Ekaterina A., Tschauner, Oliver, Walter, Michael J., and Irifune, Tetsuo. Tue . "Incorporation of high amounts of Na in ringwoodite: Possible implications for transport of alkali into lower mantle". United States. doi:10.2138/am-2016-5570. https://www.osti.gov/servlets/purl/1332403.
@article{osti_1332403,
title = {Incorporation of high amounts of Na in ringwoodite: Possible implications for transport of alkali into lower mantle},
author = {Bindi, Luca and Tamarova, Anastasia and Bobrov, Andrey V. and Sirotkina, Ekaterina A. and Tschauner, Oliver and Walter, Michael J. and Irifune, Tetsuo},
abstractNote = {In this study, 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.},
doi = {10.2138/am-2016-5570},
journal = {American Mineralogist},
number = 2,
volume = 101,
place = {United States},
year = {2016},
month = {2}
}

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