Authors: Dawson J. B.; Hill P. G.

Source: Mineralogical Magazine, Volume 62, Number 2, 1 April 1998 , pp. 179-196(18)

Publisher: Mineralogical Society

Abstract:

A peralkaline nephelinite lava ((Na+K)/Al 2.15) from the active carbonatite volcano Oldoinyo Lengai, contains combeite, Ba lamprophyllite, a phase with affinities to delhayelite, CeSrNb perovskite, a CaNa phosphate high in Sr, Ba and K, and peralkaline glass; in addition to Fe-rich nepheline, aegirine-rich clinopyroxene and FeK-rich sodalite. The high alkali concentrations relative to alumina in the bulk rock could not have been achieved by fractionational crystallisation of the known Al-rich phenocryst phases (nepheline and sodalite) and some other process must be invoked.

Keywords: OLDOINYO; LENGAI; TANZANIA; NEPHELINITE; NATROCARBONATITE; COMBEITE; BA; LAMPROPHYLLITE; DELHAYELITE; CANA; PHOSPHATE; PERALKALINE; GLASSES

Language: English

Document Type: Research article

Affiliations: 1: Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK

Publication date: 1998-04-01

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