The geology of the area to the south of Lokori, South Turkana, Kenya.

The geology of a previously unmapped area of South Turkana, lying within the Kenya Rift is described. A coloured geological map is presented. The established stratigraphic succession is largely comprised of volcanic rocks ranging in age from about 17 Ma to Recent. Volcanism is of a 'cyclic' nature, and six cycles of plateau basalt eruption followed by salic, usually trachyte central volcano activity are recognised. Particular attention is given to the morphology of multi-centred plateau basalt formations and dykes and their relationship to progressive easterly tilting - the dominant mechanism of deformation. Compared with areas to the south basic volcanism dominates the succession and the Miocene plateau phonolites are only sparsely developed. New K/Ar dates are presented but do not always confirm the established succession and often give older ages than expected. The Upper Miocene Kailimerlim trachytes appear to bo genetically related to their substrate - the Lomujal basalts. The foyaite core of this volcano however represents a separate, more undersaturated lineage. Microprobe study of phenocrysts and xenocrysts from a picrite and an ankaramite from the Lomujal basalts reveal the former to be a primary, undifferentiated magma. The latter appears to be a more differentiated basalt magma containing xenocrysts from a disrupted, cumulate sequence. Analyses of harzburgite and Iherzolite nodules from East Africa are presented eind the bulk rock chemistry of these nodules appears to control the mineral chemistry.