Magmatic segments and along-axis variations in magmatic and fault-related extension in the Main Ethiopian Rift

Magma-rich continental rifts comprise en-echelon magmatic segments where magmatism and extension are localised, similar to slow and ultra-slow spreading centres. Although this segmentation is well defined at mid-ocean ridges, it is less clearly expressed in continental rifts such as the Main Ethiopian Rift (MER). Faulting within the MER initiated at ∼11 Ma at the border faults, which define the overall NE trend of the MER and are oblique (30°–45°) to the E-W extension direction. However, since ∼2 Ma extension has localised to the right-stepping Wonji Fault Belt (magmatic segments), in which small offset faults and alignments of volcanic features strike roughly orthogonal to the extension direction. Despite this general framework, there is a lack of quantitative analysis to understand rift segmentation and its relationship to volcanic systems, and how segments interact. It is unclear how the relative contributions of magmatic and fault-related processes vary along rift segments. Using optical satellite imagery and SRTM digital elevation data with a resolution of 30 m, we investigate characteristics and scales of magmatic segments by analysing fault trace patterns, the distribution of volcanic activity, along-segment displacement variations, and elevation profiles. This is integrated with existing data, including mafic intrusions derived from gravity data, InSAR-derived locations of magma bodies, shear-wave velocities, and recent dyke intrusions between Fentale and Dofan to analyse magmatic segments. We define five magmatic segments in the MER and describe systematic decreases in fault displacement along-segment from tip to centre, which we interpret as reflecting the varying contributions of intrusion-related versus fault-related processes. The improved characterisation and understanding of the morphology of magmatic segments presented in this study will allow us to better investigate the along-rift variations in processes during magma-rich continental breakup. The MER segments share morphological and tectonic similarities with ultra-slow spreading mid-ocean ridge segments, supporting the interpretation that they represent an intermediary stage of rifting before the onset of oceanic spreading.