Stability fields of carbonates at high pressures and high temperatures have attracted considerable attention in the last years, as the fate of subducted carbon is a relevant and timely question, which needs to be answered in order to understand the deep carbon cycle. We have recently proposed a revised phase diagram for CaCO3 and discussed the implications of the aragonite – calcite VII – post-aragonite phase transitions on seismic wave velocities [1]. In a current study [2], we investigated stability fields for iron-poor dolomite, (Ca,Mg)2(CO3)2, found a new high pressure polymorph and solved the structures of dolomite-IIIc and dolomite-V. At lower p,T conditions, we explored the mechanism of the calcite – calcite-II and dolomite – dolomite-II transitions and, based on inelastic and thermal diffuse x-ray scattering studies, conclude that both phase transitions are driven by a soft phonon [3].
Acknowledgements
This research was funded by the German Science Foundation within the research unit DFG-FOR2125 “Carbonates at extreme Pressures and Temperatures” through projects BA4020 and WI1232, and through a DFG-ANR research project WI1232.
[1] Bayarjargal, L. et al. (2018) CaCO3 phase diagram studied with Raman spectroscopy at pressures up to 50 GPa and high temperatures and DFT modeling. Physics of the Earth and Planetary Interiors, 281, 31-45
[2] Binck, J. et al. (under review) High-pressure, high-temperature phase stability of iron-poor dolomite and the structures of dolomite-IIIc and dolomite-V
[3] Stekiel, M. et al. (2019) Phonon-driven phase transitions in calcite, dolomite, and magnesite. Physical Review B 99, 054101