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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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References

Clarke, M. C. G., Flegg, A. M., Le Bas, M. J. & Sutherland, D. S. 1979. Homa Mountain I: Ijolites and associated fenites. In Carbonatite–Nephelinite Volcanism: An African Case History (ed. Le Bas, M. J.), pp. 208–21. London: John Wiley and Sons.Google Scholar
Cooper, A. F., Gittins, J. & Tuttle, O. F. 1975. The system Na2CO3–K2CO3–CaCO3 at 1 kilobar and its significance in carbonatite petrogenesis. American Journal of Science 275, 534–60.CrossRefGoogle Scholar
Dawson, J. B. 1962. The geology of Oldoinyo Lengai. Bulletin Volcanologique 24, 349–87.CrossRefGoogle Scholar
Deans, T & Roberts, B. 1984. Carbonatite tuffs and lava clasts of the Tinderet Foothills, western Kenya: a study of calcified natrocarbonatites. Journal of the Geological Society of London 141, 563–80.CrossRefGoogle Scholar
Dixon, J. A. & Collins, B. A. 1977. The carbonatitic complex of North and South Ruri. In Carbonatite–Nephelinite Volcanism: An African Case History (ed. Le Bas, M. J.), pp. 169–98. London: John Wiley and Sons.Google Scholar
Flegg, A. M., Clarke, M. C. G., Sutherland, D. S. & Le Bas, M. J. 1977. Homa Mountain II: The main carbonatite centre. In Carbonatite–Nephelinite Volcanism: An African Case History (ed. Le Bas, M. J.). London: John Wiley and Sons.Google Scholar
Gittins, J. & Mckie, D. 1980. Alkalic carbonatite magmas: Oldoinyo Lengai and its wider applicability. Lithos 13, 213–5.CrossRefGoogle Scholar
Jones, W. B. & Lippard, S. J. 1979. New age determinations and the geology of the Kenyan Rift–Kavirondo Rift junction, W. Kenya. Journal of the Geological Society of London 136, 693–704.CrossRefGoogle Scholar
Katz, K. & Keller, J. 1981. Comb-layering in carbonatite dykes. Nature, London 294, 350–2.CrossRefGoogle Scholar
Larsen, E. S. 1942. Alkalic Rocks of Iron Hill, Gunnison County, Colorado. U.S. Geological Survey Professional Paper no. 197-ACrossRefGoogle Scholar
Le Bas, M. J. 1977. Carbonatite–Nephelinite Volcanism: An African Case History. London: John Wiley and Sons.Google Scholar
Le Bas, M. J. & Aspden, J. A. 1981. The comparability of carbonatitic fluid inclusions in ijolites with natrocarbonatite lava. Bulletin Volcanologique 44, 429–38CrossRefGoogle Scholar
Mccall, G. J. H. 1963. A reconsideration of certain aspects of the Rangwa and Ruri carbonatite complexes in western Kenya. Geological Magazine 100, 181–5.CrossRefGoogle Scholar
Mckie, D. & Frankis, E. J. 1977. Nyerereite: a new volcanic carbonate mineral from Oldoinyo Lengai. Tanzania. Zeitschrift für Kristallographie 145, 73–95.CrossRefGoogle Scholar
Nurse, R. W. & Midgley, H. G. 1953. Studies in the melilite solid solutions. Journal of the Iron and Steel Institute 174, 121–31.Google Scholar
Pulfrey, W. 1950. Ijolitic rocks near Homa Bay, western Kenya. Quarterly Journal of the Geological Society of London 105 (for 1949) 425–59.CrossRefGoogle Scholar
Saggerson., E. P. 1952. Geology of the Kisumu District. Geological Survey of Kenya, report no. 21.Google Scholar
Streckeisen, A. 1976. To each plutonic rock its proper name. Earth Science Reviews 12, 1–33.CrossRefGoogle Scholar