Stability and breakdown of Ca13CO3 melt associated with formation of 13C-diamond in static high pressure experiments up to 43 GPa and 3900 K

Melting of calcium carbonate Ca13CO3, stability of the melt and its decomposition were studied in static high pressure experiments at pressures of 11–43 GPa and temperatures of 1600–3900 K using diamond anvil cell technique with laser heating. We observed formation of 13C-graphite (below 16 GPa) and 13C-diamond (between 16 and 43 GPa) on decomposition of the Ca13CO3 melt at temperatures above 3400 K. At temperatures below 3400 K congruent melting of calcium carbonate was confirmed. The experimental results were applied to construction of the phase diagram of CaCO3 up to 43 GPa and 3900 K focusing at the melting curve of calcium carbonate and the decomposition phase boundary of CaCO3 melt.

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► Phase states of CaCO3 were studied at P=11–43 GPa and T=1600–3900 K.
► 13C-diamond easily crystallizes in carbonate-carbon (Ca13CO3–13C-graphite) melt-solutions.
► Ca-carbonate melts congruently that was observed in experiments in DAC with laser heating.
► Decomposition of CaCO3 melt, indicated by formation of graphite and/or diamond.
► Decomposition of CaCO3 was observed at temperatures above 3400 K in the pressure interval studied.