Phase relations of a carbonated high-CaO nephelinite at 0 center dot 2 and0 center dot 5 GPa

Experimental results for a carbonated, high-CaO evolved nephelinite at 0.2 and 0.5 GPa at 900-1040 degrees C are presented. Immiscible carbonate and s ilicate liquids are in equilibrium with a variety of crystal phases (clinop yroxene, nepheline, melilite, wollastonite, perovskite, melanite garnet, ti tanite, Fe-rich spinel, apatite and calcite). Immiscible carbonate liquids produced are high CaO and low alkali in composition. They contain significa nt Sr, Ba, F, Cl, P and are considered good analogues for natural sovite pa rent magmas. This study documents for the first time two-liquid + melilite phase assemblages in the 0.2 GPa runs, suggesting that silicate-carbonate l iquid immiscibility could be important in generating sovites associated wit h evolved nephelinites, and possibly melilite nephelinites. The two-liquid field field at 0.5 GPa is significantly wider than is observed in synthetic model systems at 0.5 GPa, being similar in size to the 1.0 GPa model syste m solvus. Results from the experiments are consistent with and confirm the geometrical arrangement of pseudoternary liquidus phase field boundaries de scribed previously for model systems. The recognition of primary calcite as a sub-liquidus phase in the experiments has important relevance to calcite -bearing, evolved nephelinites and melilitites, which are commonly observed in silicate-carbonatite complexes.