Melting and subsolidus phase relations in the system K₂CO₃–MgCO₃ at 3 GPa

ABSTRACT

As part of an investigation of carbonate systems under mantle pressures and temperatures, phase relations in the K₂CO₃–MgCO₃ system have been studied at 3 GPa and 800–1300°C. Subsolidus assemblages comprise the stability fields of K₂CO₃ + K₂Mg(CO₃)₂ and K₂Mg(CO₃)₂ + MgCO₃ with the transition boundary near 50 mol% K₂CO₃ in the system. The K₂CO₃–K₂Mg(CO₃)₂ eutectic is located at 840°C and 52 mol% K₂CO₃. The K₂CO₃ content in the melt coexisting with potassium carbonate increases to 85 mol% as temperature increases to 1050°C. K₂CO₃ remains solid up to 1250 and melts at 1300°C. K₂Mg(CO₃)₂ melts incongruently at 890°C to produce magnesite and a liquid containing 51 mol% K₂CO₃. As temperature increases to 1300°C, the K₂CO₃ content in the liquid coexisting with magnesite decreases to 27 mol%.

KEYWORDS:

• K₂CO₃–MgCO₃
• K₂Mg(CO₃)₂
• Raman
• shallow mantle
• carbonatite

Acknowledgements

This work is financially supported by the Russian Science Foundation (project No. 14-17-00609-П). The SEM and EDS studies of experimental samples were performed in the Analytical Center for multi-elemental and isotope research SB RAS. We are grateful to the anonymous reviewer for a thorough reading of the manuscript and detailed review, to Professor Hiroyuki Kagi for editorial handling, and to Nikolay S. Karmanov, Anatoliy T. Titov and Igor N. Kupriyanov for their help in analytical work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Russian Science Foundation [grant number 14-17-00609-P].