Petrogenesis of carbonatites and fenites; some recent developments

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Authors:Le Bas, M. J.
Author Affiliations:Primary:
University of Leicester, Department of Geology, Leicester, United Kingdom
Volume Title:Alkaline rocks
Volume Authors:Leelanandam, C., editor
Source:Alkaline rocks, edited by C. Leelanandam. Memoir - Geological Society of India, Vol.15, p.137-144. Publisher: Geological Society of India, Bangalore, India. ISSN: 0435-4001
Publication Date:1989
Note:In English. 32 refs.
Summary:The recent discovery of several occurrences of carbonatite lava and tephra has permitted new insight into the geochemistry of carbonatite magma. Three possible petrogenetic schemes are outlined. The genetic scheme which best explains most occurrences begins with alkali-rich carbonatite melt separating immiscibly from nephelinitic and phonolitic magmas which are themselves derived from olivine nephelinitic magma from a mantle partial melt source. After separation of the immiscible carbonate melt, the next and main stage is the fractionation of carbonatite magma by early precipitation of apatite, magnetite (depending on the oxygen fugacity) and olivine, accompanied by the loss of alkalis to the wall-rocks by fenitization. The middle and end stages of fractional crystallization of carbonatite magma are the development of magnesiocarbonatite and ferrocarbonatite followed by fluorite, Rare Earth element and related mineralizations. Contamination plays only a minor part in the evolution of carbonatite magma.
Subjects:Carbonatites; Fenite; Fluorides; Fluorite; Halides; Igneous rocks; Lava; Metals; Metamorphic rocks; Metasomatic rocks; Petrography; Phase equilibria; Pyroclastics; Rare earths; Volcanic rocks
Abstract Numbers:91M/0939
Record ID:2001071021
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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