Major and trace element partitioning between majoritic garnet and carbon dioxide-rich liquid in model carbonated peridotite at 10 GPa and interpretations of the element chemistry of majoritic garnet inclusions in diamonds from the subcontinental mantle of Brazil and Guinea

Shantanu Keshav*, Alexandre Corgne, Gudmundur H. Gudfinnsson, Yingwei Fei

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Experimentally determined major and trace element partition coefficients between majoritic garnet and carbon dioxide-rich liquid are reported at 10 GPa and 1800 °C in a model carbonated peridotite composition in the system CaO-MgO-Al2O3-SiO2-CO2. Besides majoritic garnet, the liquid coexists with forsterite, orthopyroxene, and clinopyroxene, making melting phase relations invariant at fixed pressure and temperature conditions. Partition coefficients span a wide range of values - for instance, Sr, Nb, Ba, La, and Ce are highly incompatible in majoritic garnet, while Ca, Y, Nb, and Ho are moderately incompatible, and Lu, Si, Al, and Mg are compatible. Strong fractionation of light rare earth elements (e.g., La, Ce, Nd, Sm) and high field strength elements (e.g., Nb, Ta, Zr, Hf, Th) is seen between majoritic garnet and liquid. The experimentally determined partitioning values are used to calculate compositions of melts in equilibrium with majoritic garnet inclusions in diamonds from select localities in Brazil and Guinea. The calculated melts largely straddle those between documented carbonatites, kimberlites, and alkali basalts, low-degree mantle melting products from carbonated peridotite. This resemblance firmly suggests that majoritic garnet inclusions in diamonds from Brazil and Guinea can simply be interpreted as precipitates from such melts, thereby offering an alternative to the hypothesis that the element chemistry of such inclusions in diamonds can largely, and sometimes only, be ascribed to subducted lithologies.

Original languageEnglish
Article number105486
JournalLithos
Volume362-363
DOIs
Publication statusPublished - Jun 2020

Bibliographical note

Funding Information:
The authors thank Lora Armstrong and William Minarik for their assistance in laser ablation data collection at McGill University, Canada, and Christopher Hadidiacos and David George for their help with the electron microprobe data-gathering at the Geophysical Laboratory. Referees, Ben Harte and Vincent Salters, and Editor, Michael Roden, are acknowledged for providing helpful comments on the manuscript. Carnegie Institution of Washington post-doctoral fellowships to S. Keshav and A. Corgne, and grants, NSF (EAR-0106645) to Y. Fei, EU Marie Curie (303301) to S. Keshav, and CONICYT (Fondecyt Regular 1130635) to A. Corgne, supported this research and are gratefully acknowledged.

Funding Information:
The authors thank Lora Armstrong and William Minarik for their assistance in laser ablation data collection at McGill University, Canada, and Christopher Hadidiacos and David George for their help with the electron microprobe data-gathering at the Geophysical Laboratory. Referees, Ben Harte and Vincent Salters, and Editor, Michael Roden, are acknowledged for providing helpful comments on the manuscript. Carnegie Institution of Washington post-doctoral fellowships to S. Keshav and A. Corgne, and grants, NSF ( EAR-0106645 ) to Y. Fei, EU Marie Curie ( 303301 ) to S. Keshav, and CONICYT (Fondecyt Regular 1130635 ) to A. Corgne, supported this research and are gratefully acknowledged.

Publisher Copyright:
© 2020 Elsevier B.V.

Other keywords

  • Carbonated liquids
  • Carbonated peridotite
  • Crystallization
  • Diamonds
  • Inclusions
  • Partitioning

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