Frank Zwaan, Ameha Muluneh, Jun Liu, Ehsan Kosari , Matthias Rosenau, Giacomo Corti, Federico Sani

The interaction between the NE-SW striking Main Ethiopian Rift (MER) and the E-W oriented Yerrer-Tullu Wellel Volcano-tectonic lineament (YTVL) represents one of the least understood tectonic problems in the East African Rift System. Despite the numerous studies that have been conducted in the region, the following questions still remain to be answered: did the MER and YTVL evolve simultaneously? Was there a stress reorientation to allow a diachronous evolution of the rift and the lineament? How does the E-W oriented YTVL remain active under an E-W oriented stress field? Previous studies propose a two-phase tectonic evolution, involving a stress reorientation at around 6 Ma causing deformation to focus in the MER. However, this interpretation contradicts plate-tectonic reconstruction data suggesting a constant plate divergence direction since ca. 16 Ma. We use analogue models to study how deformation may occur along the YTVL. We find that the activation of lineaments oriented (near-)parallel to the plate divergence direction is in fact possible, if (1) the weakness sufficiently reduced the strength of the crust and (2) the main rift trend is sufficiently oblique to the plate divergence direction. As such, no multiphase scenario is required to explain the development of the YTVL, and a single-phase scenario that is in line with plate tectonic reconstructions can be adopted instead. Moreover, our model results suggest that also other lineaments associated with the MER could be active in the current tectonic regime. These insights may be of relevance to the interpretation of similar structures in rift systems around the world as well.