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Phlogopitization of pyroxenite; its bearing on the composition of carbonatite magmas

Published online by Cambridge University Press:  01 May 2009

J. Gittins ,
C. R. Allen  and
A. F. Cooper
J. Gittins
Affiliation:
Department of GeologyUniversity of Toronto, Toronto, Canada, M5S 1A1
C. R. Allen
Affiliation:
Department of Mineralogy and Petrology, University of Cambridge, Cambridge, England, CB2 3EW
A. F. Cooper
Affiliation:
Geology Department, University of OtagoDunedin, New Zealand
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Summary

Phlogopitization of pyroxenite is common in contact zones between clinopyroxenites and carbonatite dikes of the Cargill ultramafic rock—carbonatite complex near Kapuskasing, Ontario. The most typical development is a mica zone 1–10 cm wide but phlogopite is also developed in a more pervasive manner throughout the groundmass of several types of ultramafic rock. Fenitization is most commonly thought of as a process whereby aegirine and riebeckitic amphiboles are formed in the host rock while feldspar is recrystallized and silica progressively removed. Phlogopitization of pyroxenite can properly be referred to, however, as a type of fenitization. It is clearly related to the intrusion of carbonatite into pyroxenite and is further testimony to the fact that many carbonatite magmas are initially alkalic but lose alkalies to the surrounding rocks and crystallize as calcitic and dolomitic carbonatite with alkali contents restricted to the amounts that could be fixed as micas, pyroxenes or amphiboles. This in turn is controlled by the silica and alumina activity of the carbonatite magma. Abundant evidence for considerable amounts of fluorine in carbonatite magmas suggests that alkalies may be transported into the country rocks as fluorides. It is further suggested that late-stage feldspathization in carbonatite complexes is explained by the abstraction of potassic halide solutions from the crystallizing carbonatite magma. The conclusion seems inescapable that alkali carbonatite magmas, far from being the curiosity thought by many petrologists, are in fact very common during the evolutionary history of carbonatites. The common calcitic and dolomitic carbonatites have not generally crystallized from a magma of the same composition but are the residue remaining after the abstraction of an alkali-rich aqueous fluid. Consequently, there is a need to redesign the experimental phase equilibrium approach to problems of carbonatite genesis in order to take account of the presence of alkalies in most carbonatite magmas.

Type
Articles
Information
Geological Magazine , Volume 112 , Issue 5 , September 1975 , pp. 503 - 507
Copyright
Copyright © Cambridge University Press 1975

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References

Cooper, A. F., Gittins, J. & Tuttle, O. F. 1975. The system Na2CO3—K2CO3—CaCO3 at 1 Kbar and its significance in carbonatite petrogenesis. Am. J. Sci. 275, 534–60.CrossRefGoogle Scholar
Currie, K. L. & Ferguson, J. B. 1971. A study of fenitization around the alkaline carbonatite complex at Callander Bay, Ontario, Canada. Can. J. Earth Sci. 8, 498–517.CrossRefGoogle Scholar
Garland, G. D. 1950. Interpretations of gravimetric and magnetic anomalies on traverses in the Canadian Shield in Northern Ontario. Pub. Dominion Observ. 16, no. 1.Google Scholar
Heinrich, E. Wm. 1966. Geology of Carbonatites. Rand McNally, New York.Google Scholar
Kopecký, L., Dobes, M., Fiala, J., & Stovickova, N. 1970. Fenites of the Bohemian Massif and the relations between fenetization, alkaline volcanism and deep fault tectonics. Sb. Geol. ved. 16, 51–112.Google Scholar
Koster van Groos, A. F. & Wyllie, P. J. 1968. Liquid immiscibility in the join NaAlSi308—Na2CO3—H2O and its bearing on the genesis of carbonatites. Am. J. Sci. 266, 932–67.CrossRefGoogle Scholar
Kukharenko, A. A. & Dontsova, E. I. 1962. The Problem of Carbonatite Genesis. Ore Deposits, 2, Nauka Press, Moscow. (In Russian.)Google Scholar
MacLaren, A. S., Anderson, D. T., Fortescue, J. A. C., Gaucher, E. G., Hornbrook, E. H. W. & Skinner, R. 1968. A preliminary study of the Moose River Belt, Northern Ontario. Paper geol. Surv. Can. 67–38.Google Scholar
McKie, D. 1966. Fenitization. In Tuttle, O. F. & Gittins, J. (Eds): Carbonatites, 261–94. Wiley-Interscience, New York.Google Scholar
Meyer, A. & Bethune, P. de. 1958. La carbonatite Lueshe (Kivu). Bull. Congo Belge Serv. geol. 8, fasc 5.Google Scholar
Morey, G. W. & Chen, W. T. 1956. Pressure—temperature curves in some systems containing water and a salt. J. Am. chem. Soc. 78, 4249–52.CrossRefGoogle Scholar
Temple, A. K. & Grogan, R. M. 1965. Carbonatite and related alkalic rocks at Powder-horn, Colorado. Econ. Geol. 60, 672–92.CrossRefGoogle Scholar
Tuttle, O. F. & Gittins, J. 1966. Carbonatites. Wiley Interscience, New York.Google Scholar
Verwoerd, W. J. 1966. Fenitization of basic igneous rocks. In Tuttle, O. F. & Gittins, J. (Eds): Carbonatites. Wiley-Interscience, New York.Google Scholar
Waldeck, W. F., Lynn, G. & Hill, A. E. 1932. Aqueous solubility of salts at high temperatures. I. Solubility of sodium carbonate from 50–348°. J. Am. chem. Soc. 54, 928–36.CrossRefGoogle Scholar
Wooley, A. R. 1969. Some aspects of fenitization with particular reference to Chilwa Island and Kangankunde, Malawi. Bull. Br. Mus. nat. Hist. 2 (4), 191–219.Google Scholar