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Published June 1971 | public
Journal Article

Experimental Study of the Composition Join NaAlSiO_4-CaCO_3-H_2O and the Genesis of Alkalic Rock--Carbonatite Complexes

Abstract

Phase equilibrium studies have been carried out on the composition join NaAlSiO_4-CaCO_3-H_2O with 25 wt per cent H_2O at 1 kb pressure in the temperature range 600–960 °C. Liquid, in equilibrium with crystalline phases and a sodic, aqueous vapor phase persists across the join down to temperatures of about 600 °C. Fractional crystallization of a carbonated nepheline-rich liquid in equilibrium with vapor is capable of generating successively the crystalline assemblages (1) nepheline, (2) melilite+nepheline, (3) hydroxyhaüyne+melilite, (4) cancrinite+melilite, and (5) calcite+cancrinite+melilite. Late-stage liquid fractions are rich in CaCO3, whereas the vapor phase is enriched in Na. The experimental assemblages are strikingly similar to rocks in alkalic rock-carbonatite complexes in general and in the Oka, Quebec, complex in particular. The succession of assemblages at Oka and at other melilite rock-bearing complexes may be interpreted as the products of fractionation of a carbonated nephelinite magma by analogy with the experimental results. The sodium-bearing vapor phase of the experiments may be analogous to the fenitizing agent of some carbonatite complexes.

Additional Information

© 1971 Oxford University Press. Received May 28, 1970. Revision received September 23, 1970. This research was supported by National Science Foundation Grants GP-1870 and GA-15718 and National Research Council of Canada Grant A5140. We thank these agencies for their support, K. Bell, G.W. Franz, J.L. Haas and A.F. Koster van Groos for stimulating discussions, and G.M. Anderson and J. Gittins for critical reviews of the manuscript.

Additional details

Created:
August 23, 2023
Modified:
October 17, 2023