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Characterization of the role of magma in driving rift basin evolution is fundamental to our understanding of how extensional plate boundaries develop. Here, we examine patterns of normal faulting, volcanism and magmatism in the South Turkana Basin, Kenya, to test how magmatism has impacted the Quaternary evolution of this system. Utilizing high-resolution, single-channel reflection seismic data and radiocarbon-dated cores, we estimate that shallow Holocene normal faulting accounts for 3.5–5.8 mm a−1 of extension, consistent with estimates farther south in the Suguta Basin. Spatial fault patterns show that extension in the Holocene is concentrated along a c. 20 km wide intra-rift fault network, aligning with the axial volcano, South Island. We suggest that up to 85% of Late Quaternary regional extension is accommodated within an axial magmatic segment rather than on the border fault system responsible for the original basin architecture. Axial extension increases towards South Island, highlighting magmatism as crucial in driving recent shallow upper crustal faulting in the South Turkana Basin. Below this zone of extensional faulting, geochemical evidence supports a developed magma plumbing system that broadly parallels equivalent axial magmatic systems within the Main Ethiopian Rift. Overall, our data support a recent (Mid- to Late Pleistocene) transition to magma-driven axial extension in the Lake Turkana rift. Supplementary material: Supplementary text and the fault, volcanic cone and radiocarbon age data utilized in this study are available at https://doi.org/10.6084/m9.figshare.c.6026624 [ABSTRACT FROM AUTHOR]

Strain localization is central to the transition between continental rifting and seafloor spreading. In the East African Rift System (EARS), there is an emerging understanding of the link between extensional pulses and magmatic episodes. We investigate modern magmatism located within the Turkana Depression and its relationship with the distribution of extensional strain. We probe the source of magmatism at South Island volcano using bulk rock, melt inclusion and olivine geochemical data and find that the magmas are derived from sub-lithospheric sources equivalent to magmatism in the more mature sectors of the rift. The depth extent of the magmatic plumbing system of South Island is constrained using vapour saturation pressures derived from bubble-corrected H2O and CO2 concentrations in melt inclusions and the results indicate a magmatic system resembling modern axial volcanic systems observed in other parts of the EARS. The zone of focused axial magmatism that South Island represents has evolved contemporaneously with a region of focused axial faulting that has accommodated the majority of regional Holocene extension and subsidence at this latitude. We conclude that at South Island there has been a migration of magmatic and tectonic strain towards the modern zone of focused intrusion along this portion of the EARS. Supplementary material: S1–S2 image files, data table files S3–S6 and caption file S7 are available at https://doi.org/10.6084/m9.figshare.c.6026627 [ABSTRACT FROM AUTHOR]