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High - pressure polymorphs of the ferroan dolomite: possible host structures for carbon in the lower mantle

Authors
/persons/resource/naira

Martirosyan,  N.
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/iliefthi

Efthimiopoulos,  I.
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Jahn,  Sandro
External Organizations;

/persons/resource/slobanov

Lobanov,  Sergey
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/wirth

Wirth,  R.
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/hanni

Reichmann,  Hans-Josef
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/mkoch

Koch-Müller,  M.
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Citation

Martirosyan, N., Efthimiopoulos, I., Jahn, S., Lobanov, S., Wirth, R., Reichmann, H.-J., Koch-Müller, M. (2023 online): High - pressure polymorphs of the ferroan dolomite: possible host structures for carbon in the lower mantle. - American Mineralogist.
https://doi.org/10.2138/am-2022-8737


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5017941
Abstract
In this study, we investigated four different ferroan dolomite samples using in situ Raman spectroscopy and powder X-ray diffraction (XRD) at high pressures up to 48 GPa and at room temperature. Our results show that the transition from Dolomite-I (Dol-I) to Dolomite-II (Dol-II) occurs above 13-16 GPa, and the transition pressure depends on the composition of the solid solution. Compression above 32-35 GPa results in the appearance of the Dolomite-IIIc (Dol-IIIc) or Dolomite-IIIb (Dol-IIIb). In the high-pressure XRD study, we found that the XRD patterns of the Ca0.97(Mg0.77,Fe0.23Mn0.03)(CO3)2 (xFe = 0.23, Ank23) can be indexed as Dol-IIIc at 44 GPa, while the rhombohedral Dol-IIIb structure matches better with the XRD patterns of the xFe = 0.40 (Ank40) and 0.64 (Ank64) solid solutions. Additionally, in the Raman spectra of the Fe-richest sample (Ca0.99(Mg0.33Fe0.64Mn0.05) (CO3)2 (Ank64), we observed an abrupt frequency downshift of the CO3-stretching vibrations between 40 – 42 GPa, which may reflect a pressure-induced Fe2+ spin transition. We further investigated two samples with xFe= 0.19 (Ank19) and 0.23 (Ank23) at high pressure and high temperatures, up to at least 2600 K. The experiments revealed that the unquenchable Dol-IIIc structure could be a stable high-pressure/high-temperature polymorph in ferroan dolomite up to at least 2600 K.