MODELING THE FLUID REGIME OF RETROGRADE METAMORPHISM ON THE BASIS OF EXPERIMENTAL-DATA ON PHASE-EQUILIBRIA IN THE SYSTEM H2O-CO2-NACL

The results of experimental study by the method of synthetic fluid inc lusion of the H2O-CO2-NaCl system at temperatures up to 700 degrees C and a pressure of 5 kbar are reported. The change in the position of i mmiscibility gap boundaries is shown. The data obtained confirm that, at low and average salinities, this ternary system inherits the charac teristics of the binary H2O-CO2 system, but the critical parameters in crease. A study of the T-P-X retrograde evolution of the Hanka Massif demonstrates that the P-T conditions varied over the temperature range of 820-450 degrees C and the pressure range of 7.4-1.2 kbar, and the mole fraction of carbon dioxide in the fluid varied from 0.31 to 0.03 at salinities of 12-20 wt %. The complex fluid evolution at simultaneo usly decreasing T-P-X parameters was as follows: the initially homogen eous fluid heterogenized at 700 degrees C (or higher). Its separated p ercolation through porous rocks was associated with a loss of carbon d ioxide, and the compositions of the immiscible portions converged. The fluid became homogeneous at temperatures below 600 degrees C and a pr essure of 3.5 kbar. The deduced evolution of the fluid phase during th e retrograde stage of metamorphism is supported by evidence from fluid inclusion and the P-T trend.