DIAMOND-FORMING MEDIA IN THE SYSTEM ECLOGITE-CARBONATITE-SULFIDE-CARBON: EXPERIMENTS AT 6.0-8.5 GPA

Abstract

Processes of diamond crystallization were experimentally studied in the model system eclogite-carbonatite-sulfide-carbon at pressures of 6.0-8.5 GPa. Diamond was synthesized for the first time in the sulfide-carbon and the eclogite-sulfide-carbon systems. Sulfide-carbon melts were produced in experiments with mixtures of graphite with chalcopyrite, pyrrhotite, and pentlandite, which are associated with both diamond and mantle peridotites and eclogites. The investigation of the eclogite-carbonatite-carbon system showed that carbonatite melts dissolved eclogitic minerals along with carbon (graphite) producing carbonate-silicate-carbon liquids. This can result in diamond crystallization together with silicate minerals and entrapment of cogenetic silicate inclusions in diamonds. According to experimental and mineralogical data, natural diamond-forming media are carbonate-silicate-carbon melts with varying chemical characteristics. They contain diverse admixtures, including sulfides. Residual melts enriched in sulfides form during the fractional crystallization of silicates and carbonates. This promotes the entrapment of sulfide inclusions by growing diamond crystals. Sulfide melts are efficient media for diamond growth. These processes are important for the genesis of diamond-bearing eclogites.