Phase Relations upon the Interaction of Phlogopite with a Carbonate Melt at P = 3.8 GPa

Phase relations in the phlogopite–carbonate system were studied at P = 3.8 GPa and T = 1200–1300°C. The interaction of phlogopite with the carbonate melt resulted in the formation of a polymineral association of relict and newly formed phases of the phlogopite–carbonate–clinopyroxene–spinel–garnet composition coexisting with the carbonate melt. Upon increasing the temperature from 1200 to 1300°C, the solubility of phlogopite and the concentrations of its components (Si, Al, Mg, and K) increase in the carbonate melt. The phase composition of the quenching phases of the carbonate melt varies from substantially carbonate with isolated microcrystals of apatite and phlogopite at 1200°C to phlogopite–carbonate with a variety of textural relationships at 1300°C, which indicates the spontaneous crystallization of the carbonate melt upon quenching. Within the studied P–T range close to the mantle adiabat, phlogopite remains stable in the presence of the silicate–carbonate melt.