Experimental Data bearing on the Role of Liquid Immiscibility in the Genesis of Carbonatites

The recognition of low-temperature melts in the system CaO—CO_2—H_2O has opened a new field of heterogeneous phase equilibrium studies in systems containing both water and carbon dioxide, the volatiles most abundant in the Earth's crust and among the most important in igneous and metamorphic processes. Liquids in this system may be regarded as simplified carbonatite magmas. The petrogenetic relationships between carbonatite magmas and the associated alkaline rocks can be examined by determining the phase relationships in systems containing CaO—CO_2—H_2O and silicate minerals. In a programme supported by the National Science Foundation, we have been investigating selected portions of complex systems in order to test the feasibility of the petrogenetic relationships which have been proposed on the basis of petrological investigations