Nephelinites and carbonatites

Saved in:
Authors:Le Bas, M. J.
Author Affiliations:Primary:
Univ. Leicester, Dep. Geol., Leicester, United Kingdom
Volume Title:Alkaline igneous rocks
Volume Authors:Fitton, J. G., editor; Upton, B. G. J.
Source:Geological Society Special Publications, Vol.30, p.53-83; Alkaline igneous rocks, Edinburgh, United Kingdom, Sept. 1984, edited by J. G. Fitton and B. G. J. Upton. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719
Publication Date:1987
Note:In English. 123 refs.; illus. incl. 8 tables, sketch maps
Summary:Carbonatites found in strongly alkaline intra-plate petrographic volcanic provinces are associated with olivine-poor nephelinites and with phonolites. Olivine-rich nephelinites occur in basanitic and alkali basalt provinces, normally without carbonatites. These igneous provinces are marked by epeirogenic crustal uplift. Nephelinites, ijolites and carbonatites form discrete magmatic events within individual complexes and correspond with the silicate-carbonate conjugate immiscible liquids observed in the laboratory. Carbonate liquids of variable alkali content can separate from both nephelinitic and phonolitic liquids. The silicate liquids give rise to pyroxenites, ijolites, nepheline syenites and nephelinitic pyroclast-rich strato-volcanoes. The carbonate liquids lose alkalis and fractionate to sovite, alvikite and ferrocarbonatite, each with increasing incompatible-element content. Further fractionation of carbonatite magma can produce mineralizing fluids rich in REE, F, Ba, U and Th. Dolomite carbonatite forms only in the deeper parts of carbonatitic complexes, perhaps at depths >2 km. Explosive carbonatite volcanism can occur giving widespread carbonate tuffs, rarely with lavas. Fenitization characterizes ijolite-carbonatite intrusive complexes. [J.M.H.]
Subjects:Alkalic composition; Carbonatites; Differentiation; Fenitization; Fractional crystallization; Genesis; Geochemistry; Igneous rocks; Magmas; Major elements; Metals; Metasomatism; Nephelinite; Phase equilibria; Processes; Rare earths; Trace elements; Volcanic rocks
Abstract Numbers:88M/2786
Record ID:1988021077
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
Tags: Add Tag
No Tags, Be the first to tag this record!
Be the first to leave a comment!
You must be logged in first