TECTONOMAGMATIC EVOLUTION OF THE EAST AFRICAN RIFT SYSTEM AS DOCUMENTED IN WEST TURKANA, KENYA

We present preliminary results for igneous rocks from West Turkana (Kenya). These were collected with the aim to better constrain the tectonomagmatic development of the Turkana Basin within the East Africa Rift System (EARS) and span a wide area ranging from the Lokitaung Gorge to Lothagam. We intend to combine new high-precision ⁴⁰Ar/³⁹Ar dating analyses with whole rock geochemistry and radiogenic isotope data. The Turkana Basin is a unique intra-domal region, where we see evidence that both magmatism and extension occur during the earliest phases of rifting. The onset of magmatism during the Late Eocene in the Turkana Basin shares the distinction of being the earliest magmatism in the EARS, together with the Amaro and Gamo tholeiitic basalts in southern Ethiopia. Magmatism continued in the Turkana Basin until modern times providing the opportunity to track the evolution of the mantle throughout the history of the basin. Previous geochemical studies in the Turkana Basin have identified sub-lithospheric mantle sources as well as a plume component but no data exist from West Turkana. The improved temporal evolution will have several applications: (a) achieve a better understanding of the role that magmatism had on rift inception and the breakage of the continental plate; (b) constrain basin development through time; (c) constrain plume dynamics and plume lithosphere interaction in west Turkana region.