Experimental study of pargasite NaCa<sub>2</sub> (Mg<sub>4</sub>Al)[Si<sub>6</sub>Al<sub>2</sub>O<sub>22</sub>](OH)<sub>2</sub> stability at T = 1000–1100°C and the pressure is u

The paper presents materials on experimental study of pargasite stability. On the example of calcic amphibole, experimental modeling of the processes occurring in the conditions of volcanic hearth at pressures up to 5 kbar was carried out. The phase diagram of pargasite was clarified. The occurring reactions and their parameters are revealed. Based on the experimental data obtained, the stability of pargasite is controlled by three reactions. The first reaction takes place in the area of low water pressure less than 1 kbar – dehydration reaction:Prg = Fo + Sp + Di + Ne + An +H2O. The second reaction takes place in the area of water pressure more than 1.2-1.5 kbar and temperature around 1100°C. Pargasite decomposition is controlled by incongruent melting:Prg = Fo + Sp +{Di+Ne +An}L+H2O. The third reaction takes place in the same pressure range as the previous one, but at lower temperatures ~1050°C. This reaction determines the pargasite liquidus in the melt and is related to the interaction between the amphibole and the coexisting melt:Prg + L= Fo + Sp + Di +{Ne +Pl}L+H2O.Presumably, the activity of the melt silicaaSiO2has the greatest impact on the pargasite liquidus.