Melting reactions in the system KAlSi ₃ O ₈ -SiO ₂ -H ₂ O to 18.5 kilobars

Abstract

Synthetic sanidine and a sanidine-natural quartz mixture were reacted with 30 to 40 percent water and the melting relations were determined to 18.5 kb. The divariant melting intervals located for each sample, along with the results of previous studies in the system, provided good estimates of the position of the univariant curves for the two reactions Or + V <--> L, and Or + Qz + V <--> L. Muscovite was present in trace amounts in all runs, including those quenched from the conditions well above its maximum T stability limit, but it was not found enclosed in glass. Thus, the muscovite was deposited from the vapor phase. Schematic phase diagrams for the system indicate that muscovite would not be expected as a stable liquidus phase for mixtures on the join KAlSi ₃ O ₈ -SiO ₂ -H ₂ O at pressures less than 10 kb.