Abstract
The paper reviews the stratigraphy, style of activity and some aspects of the petrology of Tertiary to Recent sodic alkaline volcanic rocks in Kenya, eastern Uganda and northern Tanzania.
Repeated extrusions of basaltic and nephelinitic volcanics occurred from Miocene times onwards, confirming indications from chemical data that magmas of these compositions were parental. At some central volcanoes, a basalt-trachyte-phonolite series evidently arose by fractional crystallization of basaltic magma, whereas various courses of crystallization from a nephelinitic parent led to the production of phonolites, tephrites and basanites as well as olivine-and melilite-bearing nephelinites and melanephelinites.
Phonolitic and trachytic volcanics which dominate an area of repeated upwarping (the Kenya dome) probably originated by processes of partial melting rather than by differentiation of basaltic magma. The basalt-trachyte association which characterizes many central volcanoes north and south of the dome can perhaps best be explained by postulating independent sources for the basic and salic volcanics.
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Paper read at the International Symposium « Volcanoes and Their Roots », Oxford, England, Sept., 1969.
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Williams, L.A.J. The volcanics of the gregory rift valley, east Africa. Bull Volcanol 34, 439–465 (1970). https://doi.org/10.1007/BF02596767
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DOI: https://doi.org/10.1007/BF02596767