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Tholeiite from the Simien alkali basalt centre, Ethiopia

Published online by Cambridge University Press:  01 May 2009

M. J. LeBas  and
P. A. Mohr
M. J. LeBas
Affiliation:
Department of Geology, University of Leicester, Leicester LE1 7RH, England
P. A. Mohr
Affiliation:
Smithsonian Inst. AstroPhysical Observatory, 60 Garden Street, Cambridge, Mass. 02138, U.S.A.
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Summary

The Ethiopian Cainozoic volcanics associated with the African rift system comprise one of the world's most voluminous alkaline igneous provinces. The Simien Mountains are the remnants of a Miocene alkali olivine-basalt volcanic centre in the north-western part of this province. The end-phase activity at Simien featured intrusion of dyke-swarms of two trends, one parallel to the rift system, the other almost perpendicular to it. Dykes of the rift trend are typically alkaline, but a dyke sampled from the other trend proves to be an olivine-tholeiite. Its presence is interpreted, along with similar rocks from the Harar region in eastern Ethiopia, in terms of upper mantle rifting extending from the Gulf of Aden and Red Sea under the continental blocks of the Ethiopian swell.

Type
Articles
Information
Geological Magazine , Volume 107 , Issue 6 , November 1970 , pp. 523 - 529
Copyright
Copyright © Cambridge University Press 1970

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