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The reaction 8En + Di + [1/2K2O + 1/2Na2O + H2O] = K-Rct + 2Fo was studied experimentally the presence of a K2CO3-Na2CO3-CO2-H2O fluid a temperature of 1000°C and a pressure of 3 GPa. The amphibole formation was possible at a weight ratio (K2CO3 + Na2CO3) / (CO2 + H2O) = 3/7, at Na2CO3/K2CO3 = 50/50 and 70/30. In a situation where potassium dominates over sodium, amphibole is formed only at (K2CO3 + Na2CO3) / (CO2-H2O) = 10/90. Аmphibole becomes unstable with an increase in the content of alkaline components in the fluid, a large amount of alkaline melt is present in the system. The regularities obtained in the work reproduce well the features of mineral associations and variations in component compositions in the upper mantle peridotites.