The join CaCO₃-CaSiO₃ at 6 GPa with implication to Ca-rich lithologies trapped by kimberlitic diamonds

ABSTRACT

Phase relations in the CaCO₃–CaSiO₃ system have been studied at 6 GPa and 1300–1750°C. At 1300°C, the subsolidus assemblage comprises of aragonite and walstromite. The eutectic was established at 1400°C and 57 mol% CaSiO₃. Just below its melting temperature at 1660°C, the CaCO₃ solid quenches to calcite, while, at ≤1600°C, it quenches to aragonite. At 1700°C, a walstromite + larnite + liquid assemblage appears, indicating that the system deviates from a simple binary. Incongruent melting of walstromite to produce larnite and a liquid occurs at 1750°C. The diamonds containing inclusions of walstromite and CaCO₃ could be formed as a result of the partial reduction of the CaCO₃-CaSiO₃ melt derived by melting of walstromite-bearing CaCO₃ limestones on the top of basaltic crust subducted to a depth of ≥180 km and warming to ≥1400°C.

KEYWORDS:

• CaCO₃-CaSiO₃
• Ca-rich lithology in the mantle
• aragonite
• walstromite
• superdeep diamonds

Correction Statement

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Acknowledgements

The SEM and EDS studies of experimental samples were performed in the Analytical Center for multi-elemental and isotope research IGM SB RAS. We are grateful to N.S. Karmanov, A.T. Titov and I.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 state assignment of Sobolev Institute of Geology and Mineralogy SB RAS.