| dc.description.abstract | The more important contributions of previous work to an
understanding of the structure and evolution of the Kenyarift
valley are reviewed, and the various hypotheses of origin of the
Kenya and other rift valleys are critical examined.
The distribution and present elevation of cyclic erosion
surfaces of late Cenozoicage is illustrated and it is concluded
that three principal phases of uplift of early Miocene, late ,
Miocene-early Pliocene and late Pliocene-early Pleistocene ages
occurred during the formation of the rift valley.
The distribution of the Neogenevolcanic formations is
illustrated and their sequence is established, partly from field
relationships and partly with the aid of radioisotopic age
determinations, which are listed.
The tectonics o! the structural provdnces of the rift
zone are described, and !or each an attempt is madeto trace the
sequence of volcanic and tectonic events. Theoretical aspects
of faulting in arched uplifts are considered together with the
role of pre-existing structures upon the developmentof the rift
valley. A summary of the available gravity measurements makes
it possible to deduce that crustal thinning has occurred beneath
the rift valley.
An outline of the structure and probable development of
the whole Afro-Arabian rift system is given, and it is concluded
that there is a genetic connexion between the formation of the
Red Sea and Gulf of Aden by processes akin to sea-floor spreading
and the formation of the eastern rift system of Africa. The
limitations of applying plate tectonics to eastern Africa are
analysed.
In conclusion a summary of the structural features and
evolution of the Kenya rift'valley is presented, and a mechanism
for its formation by crustal dilatation and dyke injection is
proposed. | |
