Distribution of Quaternary deformation in the central Main Ethiopian Rift, East Africa

The Main Ethiopian Rift (MER) is a narrow continental rift characterized by an along-axis variation in rift evolution, with early stages in the south evolving to incipient breakup in the north. Although distribution and style of Quaternary volcanotectonic deformation is well known in the northern rift sector, knowledge of these characteristics is comparatively less constrained southward. In this paper we present the results of a field structural study carried out to better constrain the time-space distribution of faulting in the central sector of the MER (central MER). The new field structural data coupled with new 14C radiometric dating of faulted rocks suggest a localization of faulting at both rift margins of the central MER, where radiometric dating of faulted material has allowed establishing a Late Pleistocene-Holocene activity of border faults. Conversely, in-rift faulting (Wonji Fault Belt (WFB)) is subordinate highlighting a major difference with the northern sector of the MER where deformation is essentially accommodated in the axial zone. This is consistent with an along-axis variation in rift evolution, showing the central MER less evolved than the northern rift sector. Inversion of cumulative fault slip data reveals a variation in the extension direction between the rift margins (N105°-110°E) and the rift floor (N90°-95°E), which accords well with the current Nubia-Somalia plate kinematics. The variation in extension direction across the rift could manifest a slip partitioning between the boundary faults and in-rift WFB faults.