Liquid Immiscibility in Fluid–Magmatic Systems: An Experimental Study

Abstract

Liquid immiscibility was studied in melting experiments in the system trachyrhyolite–water ± salt (NaF, Na₂CO₃) conducted at parameters imitating those of the volcanic process. The indicator components were La, Nb, Sr, W, Mo, Cr, Fe, Rb, and Cs. The experimental runs were carried out in a high gas pressure apparatus. At 1200ºC and 5 kbar, melting, homogenization, and melt saturation with fluid components occurred. A decrease in the P–T parameters to 1000°C and 1 kbar led to the onset of liquid immiscibility in the form of droplets in the melt matrix. The composition of the droplets is similar to that of the melt matrix and differs from the latter only in concentrations of water, indicator components, and proportions of alkaline and alkali-earth elements. In the presence of salt (NaF), the melt exsolved into immiscible silicate and salt melts. No liquid immiscibility was detected when Na carbonate was added to the melt, but its agpaitic coefficient increased.