The natron-engaruka explosion crater area, northern tanzania

A description is given of an explosion crater area in the eastern Rift Valley of Northern Tanzania. The features comprise maar-type explosion craters, tuff rings and tuff cones, the location of which is controlled by minor faults on the floor of the Rift Valley. In some tuff rings and cones biotite and pyroxene are common, and olivine-biotite pyroxenite is common amongst the ejected blocks. Other blocks are of ijolitic types and spinel harzburgite. The associated lavas are olivine nephelinites and olivine melilitites, which are the sodic analogues of the katungite and ugandite found in the explosion crater area in the western Rift Valley in South-West Uganda.