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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040 |a ViAlAGI  |c ViAlAGI 
041 |a eng  |b rus 
072 7 |a 05A  |2 georeft 
100 1 |a Le Bas, M. J.  |e analytic author  |u University of Leicester, Department of Geology, Leicester 
245 1 0 |a Natro carbonatites of Oldoinyo-Lengai and their parental magmas 
300 |a p. 1-9 
500 |a In English with Russian summary. 2 refs. 
500 |a Abstract number: 96M/4689 
500 |a Abstractor: R.A.H. 
500 |a Affiliation: University of Leicester, Department of Geology; Leicester; GBR; United Kingdom 
500 |a Key title: Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva = Proceedings of the Russian Mineralogical Society 
500 |a Source note: Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva = Proceedings of the Russian Mineralogical Society, 1996(2), p.1-9. Publisher: Nauka, St. Petersburg, Russian Federation. ISSN: 0869-6055 
500 |a Publication type: journal article 
504 |b 2 refs. 
510 3 |a GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom 
520 |a 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. 
650 7 |a Carbonatites  |2 georeft 
650 7 |a Genesis  |2 georeft 
650 7 |a Igneous rocks  |2 georeft 
650 7 |a Magmas  |2 georeft 
650 7 |a Melilitite  |2 georeft 
650 7 |a Nephelinite  |2 georeft 
650 7 |a Olivine nephelinite  |2 georeft 
650 7 |a P-T conditions  |2 georeft 
650 7 |a Ultramafic composition  |2 georeft 
650 7 |a Volcanic rocks  |2 georeft 
650 7 |a Volcanism  |2 georeft 
651 7 |a Africa  |2 georeft 
651 7 |a East Africa  |2 georeft 
651 7 |a East African Lakes  |2 georeft 
651 7 |a Lake Natron  |2 georeft 
651 7 |a Oldoinyo Lengai  |2 georeft 
651 7 |a Tanzania  |2 georeft 
653 |a Natrocarbonatites 
773 0 |t Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva Proceedings of the Russian Mineralogical Society  |d St. Petersburg : Nauka, 1996  |x 0869-6055  |n 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 type: journal article  |g Vol. 1996, no. 2  |h illus.