SURFACE PROCESSES AND EVOLUTION OF RIFTING IN ETHIOPIA

The Main Ethiopian Rift (MER) is characterised by along-strike variation in geometry of faults and rift evolution. In the northern MER, extensional deformation is mainly localised in narrow, dextrally offset axial segments bounded by less active mid-Miocene border faults, making it a classic example for a mature continental rift. On the contrary, in the central MER deformation is accommodated by border faults with subordinate contribution from axial faults. There also exists along-strike variation in fault geometry. In some parts, the rift is bounded by symmetric border faults on both eastern and western margin. The asymmetric sectors are mainly bounded by master faults on the eastern margin. The observed difference in deformation activity is mainly attributed to difference in magma supply, nature of the lithosphere beneath the rift and/or change in rift kinematics from roughly orthogonal to moderately oblique. Here we examine, using high resolution 2D geodynamic numerical models, the role surface processes (erosion and sedimentation) play in controlling the evolution of tectonic deformation. The sedimentation in our models include fluvial and lacustrine sediments and pyroclastic deposits. Our simulations with efficient surface processes show a concentration of high strain rate at the border faults with less activity in the rift floor faults. In models with no or less efficient surface processes, the highest strain rate is observed at the axial faults. Our study highlights the importance of surface processes in controlling along-strike variation in rift evolution.