The geology and petrology of the Hannington Trachyphonolite formation,Kenya Rift Valley

Field, petrographical and geochemical studies of a group of late Pleistocene, alkaline and mildly peralkaline trachytic and trachyphonolitic lavas from the northern Kenya Rift have been undertaken. A large number of flows were erupted from widely dispersed centres to form an extensive volcanic shield within the floor of the rift. The major element composition of most rocks was substantially modified during crystallisation, but other data show that differentiation within the suite was the result of protracted feldspar fractionation of a trachytic magma with intially very low abundances of residual trace elements.