GEOCHEMICAL CHARACTERIZATION OF DIKES AND LAVA FLOWS IN LOPEROT, KENYA

The East African Rift (EAR) is an intra-continental rift system of basins and rift valleys that spans ~3000km from the Afar triple junction to Mozambique. This rift system separates two diverging plates, the Somalian and African plates, and splits around the Tanzanian Craton into two segments: the Eastern Branch and the Western Branch. The Turkana Basin sits between the Ethiopian and Kenyan Domes, which are topographically elevated due to the thermal anomaly of impinging mantle plume(s). Volcanic activity in eastern Africa has been ongoing since the Eocene and continues today. The area of focus is Loperot (Kenya), a known fossiliferous site located in the southwest of the Turkana Basin. This study is part of a collaborative effort, the Turkana Miocene Project, and has two goals: to better constrain the fossils and paleontology records from Turkana and to better understand volcanism and extensional forces from the Miocene to the present. We collected 12 samples from 5 lava flows and 7 dikes from the area surrounding the existing Loperot stratigraphic section (LpM4) and fossil locality. Here, we examine their geochemical signature to reconstruct the magmatic evolution of the area. The samples were selected with the aim of collecting diverse lava flows and dikes based on their textural appearance, orientation, and relative stratigraphic position. The samples were crushed to be analyzed for whole rock geochemistry using XRF and ICP-MS. When plotted on a TAS diagram, the Loperot lavas cluster along three distinct liquid lines of descent, indicating the presence of varying magma sources. All dikes and two related lava flows are trachybasalts to trachyandesites clustering in a group with Na₂O+K₂O ranging from 6-9, low TiO₂ (2-2.5), and FeOt from 9-12. A single basaltic trachyandesite sampled from a lava flow at the top of the LpM4 section plots at intermediate compositions with a Na₂O+K₂O of about 6, higher TiO₂ (2.5-3), and FeOt around 13. A third group is represented by two basaltic andesite lava flows sampled stratigraphically above the previous one at LpM4 and overlaying a nearby well, supporting their stratigraphic correlation. These have Na₂O+K₂O around 4-5, higher TiO₂ (2.5-3) and higher FeOt (13-14). These three lavas have distinct chemical compositions and allow us to isolate distinct magmatic events in the region.