Natro carbonatites of Oldoinyo-Lengai and their parental magmas

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Authors:Le Bas, M. J.
Author Affiliations:Primary:
University of Leicester, Department of Geology, Leicester, United Kingdom
Volume Title:Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva Proceedings of the Russian Mineralogical Society
Source:Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva = Proceedings of the Russian Mineralogical Society, 1996(2), p.1-9. Publisher: Nauka, St. Petersburg, Russian Federation. ISSN: 0869-6055
Publication Date:1996
Note:In English with Russian summary. 2 refs.; illus.
Summary:This article is an essay-review of the book Carbonatite Volcanism: Oldoinyo-Lengai and the Petrogenesis of Natrocarbonatites, edited by K. Bell & J. Keller (IAVCEI Proceedings in Volcanology, 4, 1995, 210 pp). The first three chapters deal with volcanological field observations and the physical properties of the lavas. The next six chapters examine the petrology and geochemistry, and the last four consider the petrogenesis. The 1988 natrocarbonatite lavas carry phenocrysts of nyerereite and gregoryite; the only silicate is tentatively identified as an alkaline-REE-Fe variant of spurrite. One conclusion concerning the petrogenesis of natocarbonatite is that it was derived from an Na-rich olivine melilitite, which after fractionation separated immiscibly into two liquids, one natrocarbonatite and the other a wollastonite nephelinite which in turn fractionates to a combeite nephelinite. The isotope geochemistry of natrocarbonatite agrees with a mantle source, but its trace elements and REE show it to be highly fractionated unlike any other known carbonatite. It is suggested that these carbonatite magmas at Oldoinyo Lengai fractionated in a 'closed system', with no exchange with groundwaters and no loss of alkalis. [R.A.H.]
Subjects:Carbonatites; Genesis; Igneous rocks; Magmas; Melilitite; Nephelinite; Olivine nephelinite; P-T conditions; Ultramafic composition; Volcanic rocks; Volcanism; Africa; East Africa; East African Lakes; Lake Natron; Oldoinyo Lengai; Tanzania; Natrocarbonatites
Abstract Numbers:96M/4689
Record ID:1997030815
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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