Potassium—Argon Ages from the Volcanic Province of Northern Tanzania

Abstract

THIS letter reports dates for samples from the volcanic centres east of the main Manyara-Natron fault escarpment of northern Tanzania obtained by the potassium-argon method. The sequence of the Kenyan volcanics has recently been established using potassium-argon age determinations (personal communication from B. H. Baker et al.). During the Miocene both multicentre alkali-basalt eruptions and nepheline-phonolite-carbonatite centres occurred in central and northern Kenya. Volcanic activity forming phonolite and trachyte lavas continued throughout the Pliocene and Pleistocene in central and southern Kenya. The last major volcanic phase was during the Quaternary, with intense fracturing accompanying the volcanic eruptions along the rift floor. The volcanic province of northern Tanzania is the southern limit of both the Gregory rift volcanic zone and the grid faulting which characterizes the rift floors of Kenya and Ethiopia, with the exception of volcanic centres occurring in central and southern Tanzania which have not been dated.