The systems KCl–CaCO₃ and KCl–MgCO₃ at 6 GPa

ABSTRACT

Continuous variations in the composition of melt inclusions in diamonds from K-rich saline to carbonatitic indicate their possible genetic relationship. This causes interest in the study of chloride-carbonate systems at high pressure. Here we present experimental data on phase relations in the KCl–CaCO₃ and KCl–MgCO₃ systems at 6 GPa and 1000–1600 °C. The studied systems have the eutectic type of T-X diagrams. Subsolidus phases are represented by aragonite + KCl and magnesite + KCl. The KCl–CaCO₃ eutectic is situated at 1200 °C and K2# 20, while the KCl–MgCO₃ eutectic is located at 1400 °C and K2# 43, where K2# = 2KCl/(2KCl + CaCO₃+ MgCO₃)×100 mol%. The concentration of K and Cl in water-soluble chloride, and Ca, Mg, and CO₂ in carbonate suggests that K-rich saline fluid entrapped by ‘fibrous’ diamonds could be a low-temperature derivative of a carbonatite melt containing KCl and H₂O.

KEYWORDS:

• Chloride
• carbonate
• KCl
• melting
• T-X diagram
• Earth’s mantle

Acknowledgments

We thank three anonymous referees for comments, which improved the manuscript. This work is financially supported by Russian Science Foundation (project No 21-17-00024).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Russian Science Foundation: [grant number 21-17-00024].