Effects of hydrostaticity on the structural stability of carbonates at lower mantle pressures: the case study of dolomite

ABSTRACT

We have conducted high pressure far-infrared absorbance and Raman spectroscopic investigations on a natural iron-free dolomite sample up to 40 GPa. Comparison between the present observations and literature results unraveled the effect of hydrostatic conditions on the high pressure dolomite polymorph adopted close to 40 GPa, i.e. the triclinic Dol-IIIc modification. In particular, non-hydrostatic conditions impose structural disorder at these pressures, whereas hydrostatic conditions allow the detection of an ordered Dol-IIIc vibrational response. Hence, hydrostatic conditions appear to be a key ingredient for modeling carbon subduction at lower mantle conditions. Our complementary first-principles calculations verified the far-infrared vibrational response of the ambient- and high pressure dolomite phases.

KEYWORDS:

• Dolomite
• high pressure
• vibrational spectroscopy
• hydrostaticity
• first-principles

Acknowledgements

We thank Wilhelm Heinrich for providing us with the natural dolomite samples. We thank Helmholtz-Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtime.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Ilias Efthimiopoulos http://orcid.org/0000-0001-6542-8188

Notes

1. We remind here that the most recent high pressure XRD investigation indicated the adoption of a triclinic Dol-IIIc polymorph at 41.5 GPa (neon PTM, RT) for a Fe-free dolomite sample [27], rather than the previously reported (also triclinic) Dol-III structure [9]; since our sample was also a Fe-free dolomite, we will be using the Dol-IIIc nomenclature in the present paper.

2. We note that the DFT calculated Dol-I→Dol-II transition pressure is bracketed between 10 and 18 GPa, depending on the exact theoretical approximation [28].

Additional information

Funding

This study was partly supported by a Grant from Deutsche Forschungsgemeinschaft (DFG) within the Research Unit FOR2125 CarboPaT under Grants KO1260/16 and JA1469/9.