Abstract
AbstractThe distribution of Tertiary to Recent lavas in part of south-west Kenya is outlined, and attention drawn to the predominance of nepheline-rich Miocene lavas over other types west of the Rift Valley, which contrasts with the Pliocene olivine basalt-trachytecomendite association predominating within the Rift Valley. It is inferred that widespread Miocene phonolites west of the Rift Valley derived from a parent of approximate mela-nephelinitic composition, while within the Rift Valley extensive Pleistocene trachytes differentiated from an olivine basaltic parent. Plots of normative feldspathoid: feldspar versus silica, for analysed lavas from Kenya and Tanganyika, are used to illustrate the trends envisaged. The frequent association of nephelinitic lavas and carbonatite complexes in Kenya is discussed and the possibility mooted that the presence of nephelinite lavas may be indicative of nearby carbonatite complexes.
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