Experimental Modeling of C⁰-Forming Processes Involving Cohenite and CO₂-Fluid in a Silicate Mantle

Abstract: Experimental studies were performed in the Fe₃C–SiO₂–(Mg,Ca)CO₃ system (6.3 GPа, 1100–1500°C, 20–40 h). It is established that the carbide–oxide–carbonate interaction leads to the formation of ferrosilite, fayalite, graphite, and cohenite (1100 and 1200°С), as well as a Fe–C melt (1300°С). It is determined that the main processes in the system are decarbonation, redox-reactions of cohenite and a CO₂-fluid, extraction of carbon from carbide, and crystallization of metastable graphite (± diamond growth), as well as the formation of ferriferous silicates. The interaction studied can be considered as a simplified model of the processes that occur during the subduction of oxidized crustal material to reduced mantle rocks.