Chyulu Hills

The Chyulu Hills lie to the northeast of Kilimanjaro (Fig. 90) and are a northwest-southeast trending range, much of which is covered by Pleistocene to Recent lava flows up to 16 m thick. Only the northwestern part of the hills have been mapped in detail (Searle, 1954; Saggerson, 1963). In the Simba-Kibwezi area (Saggerson, 1963) 367 volcanic vents were recognised, principally scoria cones, which form linear groups parallel to the general trend of the hills and many of these, because of their comparatively recent age, have suffered little erosion. All the volcanic rocks, which includes lavas, agglomerates and ashes, are basalts but the lowermost in the Simba-Kibwezi area are basanites containing fresh analcime. Analyses of whole rocks are given by Saggerson (1963) and Goles (1975) and indicate up to 12% normative nepheline; the latter paper contains some trace element data. Pyroxenite, peridotite and granulite xenoliths are described by Henjes-Kunst and Altherr (1992), these authors indicating that rare nephelinite has been found in the Chyulu Hills.