Amboseli Area

The southern half of the Amboseli area, which lies adjacent to the border with Tanzania, is covered extensively by lavas of the Kilimanjaro volcano, (see Tanzania No. 163-00-022). Although much of the lava emanated from eruptive centres within the Amboseli area itself some flowed northwards from the Kibo centre of Kilimanjaro. Further Kilimanjaro products are found in the Taveta area to the southeast (No. 085-00-074), but the area immediately east of Amboseli has not been geologically surveyed in detail, although it is known to include extensive areas of lava (see Fig. 90). A full petrographical account of the Amboseli volcanic rocks is given by Williams (1972b) who also presents detailed correlations with the main succession on Kilimanjaro. He divides the volcanic rocks into seven groups which, in ascending order, are: (1) olivine basalt, feldsparphyric olivine basalt, mugearitic basalt and basanite; minor intercalations of pyroclastic rocks, (2) ankaratrite, melanephelinite, nephelinite, tephrite and phonolite, (3) feldsparphyric olivine basalt and mugearitic olivine basalt, (4) nephelinite, ankaratrite and melanephelinite, (5) olivine rhomb porphyry, (6) olivine phonolitic trachyte and basalt, and (7) phonolite. The total thickness at the Tanzania border is about 1000 m of which the lowermost basalt group comprises approximately half. It is noteworthy that amongst Williams’ ‘Upper nephelinites’ (group 4 above) are melilite-melanite-perovskite nephelinites while his youngest rocks, the phonolite of group (7), correlate with the ‘Inner Crater Group’ of workers on Kilimanjaro and are the furthest extent of a flow originating in the main crater. Williams (1972b) gives 14 whole rock analyses of lavas.