Peculiarities of Fe penetration into the matrix of CaCO₃ ± olivine ± serpentine at a pressure of 4 GPa and temperature of 1400-1500°C (experimental data)

Research subject. We present the first results on modeling of the interaction of CaCO₃ with metallic Fe in the presence of olivine and serpentine at high P-T parameters in comparison with the CaCO₃-Fe system. The relevance of the study is related to the need to study decarbonatization reactions during subduction of crustal matter into the Earth's reduced mantle within the context of the global carbon cycle. Methods. The experiment was carried out using a BARS high-pressure apparatus at a pressure of 4.0 GPa and temperatures of 1400-1500°С with a subsequent study of the obtained samples on a scanning electron microscope equipped with a chemical microanalysis system. Results. CaCO3 was found to be unstable under the implemented conditions. The reaction products were iron carbide and Ca-wustite or Ca-magnesiowustite in the presence of silicate phases. Conclusions. The interaction of CaCO₃ with metallic Fe at high pressure occurs even if the components are in the solid state. High reaction rates during interaction are provided by the appearance of liquid metal due to the relatively low melting temperature of the eutectic in Fe-C systems. The influence of gravity on the penetration of Fe into the carbonate matrix, which consists in the predominant infiltration of liquid metal between carbonate grains, was established. The presence of H₂O significantly reduces the melting point of carbonate, which leads to an increase in the diffusion of components and decarbonization reaction rate, while the effect of gravity also takes place due to the difference in the density of liquid Fe in comparison with other components in a highly fluidized environment.

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