Аннотация:The paper presents the experimental results of phlogopite formation in the grossular–pyrope–enstatite + H2O–KCl system at 3 GPa and 850°C, also at 5 GPa and 1000°C. It was established that an increase of the salt component in the fluid leads to the decomposition of aluminum–containing minerals, such as enstatite and garnet, as well as the formation of phlogopite and diopside. The amount of aluminum in enstatite decreases, and the amount of chlorine in phlogopite increases with increasing XKCl in the fluid. In experiments at XKCl = 0.05, 0.1 T = 1000 ° C, and also in experiments at XKCl = 0.1 T = 850 ° C, XGrs in garnet increases, which can explained by the two different reactions: 1/2Prp + 3/2En + [1/2K2O + H2O] = Phl and Di + 0.8CaTs + 0.3KCl + 0.2H2O = 0.6Grs + 0.2Phl + 0.2Cl-Phl. At XKCl = 0.2 XGrs in garnet decreases, which is explained by the reaction 1/2Prp + 1/2Grs + 6En + [2KCl + H2O] = 1/2Phl + 1/2Cl-Phl + 3/2Di. The established effects are good indicators of KCl activity in the fluid during the process of modal mantle metasomatism.