EXPERIMENTAL STUDY OF DIAMONDITE FORMATION IN CARBONATE-SILICATE MELTS: A MODEL APPROACH TO NATURAL PROCESSES

To simulate a natural carbonate-silicate medium parental for both diamondites and their syngenetic mineral inclusions, melanocratic carbonatites of the Chagatai complex, Uzbeki-stan, were used. The carbonatites are characterized by a high percentage of silicate components and high-pressure eclogitic silicate minerals. The experiments carried out at 7.0–8.5 GPa and 1800 °C show that the diamondites formed very quickly in C-enriched carbonate-silicate melts of the Chagatai carbonatites. According to experimental evidence, the mineralogy of the Chagatai carbonatites under P-T conditions of diamondite formation is represented by grossular-almandine garnet, diopside-hedenbergite clinopyroxene, and calcite (aragonite) and resembles the mineralogy of diamond-bearing Ca-rich eclogites and grospydites found in kimberlites as mantle xenoliths. The Chagatai carbonatites are quite appropriate as a parental medium to simulate physicochemical processes for the formation of natural diamondites. The most important characteristics of these processes are as follows: quick migration of mobile low-viscosity carbonate-silicate melts into zones of diamondite formation, extremely high “snowballing ” rate of diamondite crystallization from a carbon-ate-silicate melt oversaturated with dissolved carbon, formation of syngenetic inclusions of garnet and clinopyroxene, carbonate and sulfides, etc. inside the pores and cavities of diamondites. Experiments show that the formation of diamondites and their syngenetic inclusions is accompanied by coarse-grained crystallization of eclogitic minerals in the parental media surrounding the growing diamondites. Syngenesis of diamondites and inclusions, carbonate parental melts, experimen