NEW INSIGHTS INTO THE CRUSTAL STRUCTURE OF THE MAGMA-RICH TURKANA RIFT ZONE IN THE EAST AFRICAN RIFT SYSTEM

Studies on the crustal structure of the Turkana Rift Zone (TRZ) in northern Kenya and southern Ethiopia began in the early 1980s. Initially driven by hydrocarbon exploration, these studies revealed that the rift zone comprises multiple fault-bounded basins ranging in age from the Eocene to the present. They also showed that the area hosts the intersection zone of the N-S trending basins of the Cenozoic East African Rift System (EARS) and the NW-SE-trending Mesozoic-Paleogene Central African Rift System (CARS). However, early seismic reflection and borehole data were mostly concentrated in the southern TRZ, resulting in limited subsurface data for its northern counterpart. This data gap has led to an incomplete understanding of the rift zone's regional crustal structure and how earlier CARS-related rifting influenced the development of the present-day EARS.

Here, we leverage newly collected onshore and offshore subsurface industry datasets in the TRZ, spanning a 300 x 150 km region, to characterize the TRZ's crustal structure. We map several key subsurface horizons using a dense grid of 363 2-D seismic reflection profiles, which we tie to surface geology and borehole datasets. Mapping the acoustic basement produced new structure contour maps that provide high-resolution constraints on the TRZ’s crustal structure. Additionally, our isopach maps of key horizons show that strain migrated toward the modern rift axis, located along the center of Lake Turkana, following the widespread eruption of the Gombe Group basalt around 4 million years ago. Together, these results indicate that the area of maximum subsidence is collocated with the area transected by the CARS. Thus, we propose that these earlier episodes of rifting may have influenced the development and evolution of the modern EARS in the northern TRZ. These results provide crucial information for understanding tectonics in the context of hominin evolution and offer new insights into forming a divergent plate boundary.