Phase relations of a Carbonated High-CaO Nephelinite at 0.2 and 0.5 GPa
Journal of Petrology
Experimental results for a carbonated, high-CaO evolved nephelinite alkali silicate melt via liquid immiscibility (von Eckerat 0·2 and 0·5 GPa at 900-1040°C are presented. Immiscible mann, 1961 Koster van Groos & Wyllie, 1963); and carbonate and silicate liquids are in equilibrium with a variety crystal fractionation of carbonated alkali silicate melts of crystal phases (clinopyroxene, nepheline, melilite, wollastonite, (King, 1949; Watkinson & Wyllie, 1971 ). There is, howperovskite, melanite
... rovskite, melanite garnet, titanite, Fe-rich spinel, apatite and ever, a growing body of published papers which taken calcite). Immiscible carbonate liquids produced are high CaO and together support the notion that carbonatite magmas can low alkali in composition. They contain significant Sr, Ba, F, Cl, be generated by all three processes described above. The P and are considered good analogues for natural sövite parent merits of primary mantle melting to produce carbonatite magmas. This study documents for the first time two-liquid + magmas are not discussed in this paper. Rather, the melilite phase assemblages in the 0·2 GPa runs, suggesting that generation of carbonatite magmas by 'secondary' (liquid silicate-carbonate liquid immiscibility could be important in genimmiscibility and crystal fractionation) processes at miderating sövites associated with evolved nephelinites, and possibly to upper-crustal levels is examined. melilite nephelinites. The two-liquid field at 0·5 GPa is significantly Fruitful day-long discussions in 1988 and 1989 with wider than is observed in synthetic model systems at 0·5 GPa, John Gittins in Toronto, on the drawbacks and merits being similar in size to the 1·0 GPa model system solvus. Results of the liquid immiscibility hypothesis, resulted, in part, from the experiments are consistent with and confirm the geometrical in a reassessment of previous experimental rationale. In arrangement of pseudoternary liquidus phase field boundaries departicular, Gittins stressed the importance of sub-liquidus scribed previously for model systems. The recognition of primary experiments to explore a variety of problems not excalcite as a sub-liquidus phase in the experiments has important amined specifically by Kjarsgaard & Hamilton (1988, relevance to calcite-bearing, evolved nephelinites and melilitites, 1989a, 1989b. These ideas, taken in conjunction with which are commonly observed in silicate-carbonatite complexes.