Abstract
Near Lokitaung in the northernmost part of the Turkana area, transitional tholeiitic basalts about 30 m.y. old overlie the Turkana grits. Coeval, essentially alkaline «basalts» outcrop in the neighbouring zone of Kalin. These rocks represent the southernmost occurrences of the great and extended volcanism which took place in Ethiopia and in part of the Arabian peninsula in Oligocene times. The ascription of the Oligocene Turkana basalts to the Ethiopian volcanic activity is supported by structural, volcanological, geochemical and mineralogical analogies with coeval lavas from N and S Ethiopia. In this respect, clinopyroxene composition resulted to be especially meaningful. In the course of the Oligocene volcanic activity, basic magmas changed their composition at a rate which varied from zone to zone. This rate is considered to be depended on whether the considered zones occupy a more or less peripheral position with respect to the Ethiopian dome.
Published Version
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