The system CaO-SiO2-CO2-H2O—III. Second critical end-point on the melting curve

摘要: Melting relationships in the system CaO-SiO_2-CO_2-H_2O have been extended to 40 kbar pressure. Dellaite, dicalcium silicate, spurrite and ealciochondrodite appear as silicate phases coexisting with vapor-saturated liquids fluids at high pressures. Contrary earlier predictions, wollastonite does not on liquidus, least pressures below 10 kbar. The solidus terminates a second critical end-point about 32.5 515°C. To provide model for our results this quaternary system, phase hypothetical ternary end-points are developed. An extension of these into shows that curve limiting miscibility gap between vapors moves through changing pressure, terminating series univariant reactions end-points. applicable origin carbonatites associated alkalic rocks kimberlites they illustrate fractional crystallization will produce carbonatitic melts only from originally undersaturated silica, pressure range prevailing within earth's crust.