The system MgC[O.sub.3]-FeC[O.sub.3]-CaC[O.sub.3]-[Na.sub.2]C[O.sub.3] at 12-23 GPa: phase relations and significance for the genesis of ultradeep diamonds

Physical-chemical experimental studies at 12-23 GPa of phase relationships within four-members carbonate system MgC[O.sub.3]-FeC[O.sub.3]-CaC[O.sub.3]-[Na.sub.2]C[O.sub.3] and its marginal system MgC[O.sub.3]- FeC[O.sub.3]-[Na.sub.2]C[O.sub.3] were carried out. The systems are quite representative for a set of carbonate phases from inclusions in diamonds within transitional zone and lower mantle. PT-phase diagrams of multicomponent carbonate systems are suggested. PT parameters of boundaries of their eutectic melting (solidus), complete melting (liquids) are established. These boundaries define area of partial melting. Carbonate melts are stable, completely mixable, and effective solvents of elemental carbon thus defining the possibility of ultra-deep diamonds generation. DOI: 10.1134/S1028334X15090135