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1966 ash eruption of the carbonatite volcano Oldoinyo Lengai: mineralogy of lapilli and mixing of silicate and carbonate magmas

Published online by Cambridge University Press:  05 July 2018

J. B. Dawson ,
J. V. Smith  and
I. M. Steele
J. B. Dawson
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW
J. V. Smith
Affiliation:
Department of the Geophysical Sciences, University of Chicago, Illinos 60637, U.S.A.
I. M. Steele
Affiliation:
Department of the Geophysical Sciences, University of Chicago, Illinos 60637, U.S.A.
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Abstract

Lapilli from the August 1966 eruption of the carbonatite volcano Oldoinyo Lengai consist of carbonate-cemented aggregates of (i) mono- and poly-mineralic fragments of ijolitic rocks, (ii) single grains and clusters of euhedral nepheline, Ti-andradite, and Ti-magnetite, and (iii) corroded pyroxene and wollastonite grains surrounded by coronas containing combeite, melilite, Ca-silicates (possibly larnite and rankinite), and rounded bodies of submicrometre intergrowths with complex bulk compositions dominated by Na,K,Ca-phosphate-carbonate and alkali-iron-sulphide-carbonate. The (ii,iii) materials, together with abundant Na-carbonate, sylvite and fluorite occurring as cement and shells in the lapilli, are attributed to mixing and incomplete reaction of ijolite and carbonatite magmas during the explosive eruption. The rounded submicrometre intergrowths are interpreted as the quench products of two types of immiscible liquids whose properties should be studied by controlled synthesis.

Keywords

carbonatitesilicatecarbonatemagmasOldoinyo Lengaiash
Type
Research Article
Information
Mineralogical Magazine , Volume 56 , Issue 382 , March 1992 , pp. 1 - 16
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2014

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