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Carbonated melilitites and calcitized alkalicarbonatites from Homa Mountain, western Kenya: a reinterpretation

Published online by Cambridge University Press:  01 May 2009

M. G. C. Clarke  and
B. Roberts
M. G. C. Clarke
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
B. Roberts
Affiliation:
Geology Department, Birkbeck College, 7–15, Gresse Street, London W1P 1PA, U.K.
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Abstract

Homa Mountain is a well developed ijolite/carbonatite complex of Miocene to Quaternary age. Late stage olivine melilitite occurs as a satellite plug, parts of which show strong deuteric alteration to carbonate resulting in complete pseudomorphing of the melilite.

A second satellite centre exposes a grey carbonate tuff and accompanying dykes, all of which exhibit relic textures after an elongate, rectangular mineral also formerly believed to be melilite. Comparison with other recently described occurrences indicates however that the second centre erupted alkali-carbonatite and that the chief mineral originally present was nyerereite (Na2Ca(CO3)2). The field relationships and petrographic characters of both rock types are described and criteria are given which permit distinction between carbonated melilite and calcitized nyerereite. It is concluded that olivine melilitite and alkalicarbonatite are closely related in space and time.

Type
Articles
Information
Geological Magazine , Volume 123 , Issue 6 , November 1986 , pp. 683 - 692
Copyright
Copyright © Cambridge University Press 1986

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