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Extrusive carbonatites: their origins reappraised in the light of new experimental data

Published online by Cambridge University Press:  01 May 2009

John Gittins  and
Bruce C. Jago
John Gittins
Affiliation:
Department of Geology, University of Toronto, Toronto M5S 3B1, Canada
Bruce C. Jago
Affiliation:
Department of Geology, University of Toronto, Toronto M5S 3B1, Canada
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Abstract

Calcite-rich carbonatites are commonly attributed to calcitization of alkalic carbonatite of Oldoinyo Lengai type. The interpretation arises from the presumption that magmatic crystallization of calcite at atmospheric pressure is not possible. We show that only a small percentage of fluorine, a common element in carbonatite magmas, permits such crystallization, and we argue that most of the calcite in extrusive carbonatites is magmatic. The presence of any more than minor apatite precludes an alkalic carbonatite parentage. While not denying that calcification of alkalic carbonatite can occur, we suggest that it is not generally responsible for the formation of extrusive calcific carbonatites.

Type
Articles
Information
Geological Magazine , Volume 128 , Issue 4 , July 1991 , pp. 301 - 305
Copyright
Copyright © Cambridge University Press 1991

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