The Effect of CO2 Saturation on Immiscibility between Silicate and Carbonate Liquids: an Experimental Study

Experiments at 1250°C and 25 kbar are used to illustrate the maximum extent of the silicate–carbonate immiscible liquid field in a multicomponent system and the effects of CO2 undersaturation. The results demonstrate the dramatic expansion of the two-liquid field as PCO2 is increased to approach Ptotal. The response of the system to CO2 undersaturation is used to reconcile differences between previous data sets, which apparently indicated an expansion of the two-liquid field from 0.7 to 7 kbar, followed by a substantial contraction to 25 kbar. This effect appears to be the result of comparing CO2-saturated and -undersaturated data. The fully expanded, CO2-saturated, multicomponent two-liquid field at 25 kbar may approach the melt compositions formed at mantle pressures, and an immiscible origin for carbonatites in the mantle cannot be excluded on the basis of the experimental data.