Phlogopite Formation in the Orthopyroxene-Garnet System in the Presence of H_2O-KCl Fluid in Application to the Processes of Mantle Metasomatism

摘要

The results of experimental studies are presented for reactions in the orthopyroxene-garnet-phlogopite system in the presence of H2O-KCl fluid at 3-5 GPa and 900-1000 degrees C, which model the processes of phlogopite formation in garnet peridotites and pyroxenites during alkaline metasomatism of the upper mantle. The experiments demonstrated regular variations in the composition of garnet, pyroxenes, and phlogopite depending on the KCl content of the fluid. With increasing KCl content of the fluid, enstatite and garnet become unstable, the Al2O3 content of enstatite decreases, and the amount of grossular and knorringite components in garnet are maximum at a KCl content of similar to 10 mol %. Our results illustrate well the regular variations in the compositions of the coexisting minerals and their zoning in phlogopite-bearing peridotites of the lithospheric mantle.