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Synthesis of calcium orthocarbonate, Ca2CO4-Pnma at P-T conditions of Earth’s transition zone and lower mantle

Authors
  • Binck, Jannes1
  • Laniel, Dominique2
  • Bayarjargal, Lkhamsuren1
  • Khandarkhaeva, Saiana3
  • Fedotenko, Timofey2
  • Aslandukov, Andrey2
  • Glazyrin, Konstantin4
  • Milman, Victor5
  • Chariton, Stella6
  • Prakapenka, Vitali B.6
  • Dubrovinskaia, Natalia2
  • Dubrovinsky, Leonid3
  • Winkler, Björn1
  • 1 Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, 60438 , (Germany)
  • 2 Laboratory of Crystallography, University of Bayreuth, 95440 , (Germany)
  • 3 Bayerisches Geoinstitut, University of Bayreuth, 95440 , (Germany)
  • 4 Photon Science, Deutsches Elektronen-Synchrotron, Notkestrasse 85, 22607 , (Germany)
  • 5 BIOVIA Dassault Systèmes, 334 Science Park, CB4 0WN , (United Kingdom)
  • 6 Center for Advanced Radiation Sources, The University of Chicago, Illinois 60637 , (United States)
Type
Published Article
Journal
American Mineralogist
Publisher
Mineralogical Society of America
Publication Date
Feb 25, 2022
Volume
107
Issue
3
Pages
336–342
Identifiers
DOI: 10.2138/am-2021-7872
Source
De Gruyter
Keywords
License
Yellow

Abstract

We show, by single-crystal diffraction studies in laser-heated diamond-anvil cells, that Ca2CO4 orthocarbonate, which contains CO44− tetrahedra, can be formed already at ~20 GPa at ~1830 K, i.e., at much lower pressures than other carbonates with sp3-hybridized carbon. Ca2CO4 can also be formed at ~89 GPa and ~2500 K. This very broad P-T range suggests the possible existence of Ca2CO4 in the Earth’s transition zone and in most of the lower mantle. Raman spectroscopy shows the typical bands associated with tetrahedral CO44−-groups. DFT-theory based calculations reproduce the experimental Raman spectra and indicate that at least in the athermal limit the phase assemblage of Ca2CO4 + 2SiO2 is more stable than 2CaSiO3 + CO2 at high pressures.

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