Structural Architecture, Kinematics and Strain Partitioning of the Hayk-Ardibo Marginal Graben: Implications for Poly-Phase Extension Along the Afar Margin Ethiopia

The Hayk-Ardibo basin of the Western Afar Margin is a key structural transition zone between the elevated Ethiopian Plateau and stretched Afar Depression. It contains important information about continental rifting processes. Using high resolution (30 m) SRTM DEM derived lineaments, meso-scale field observations, stereonet stress tensors and balanced cross-sections, we have investigated the geometries, kinematics, evolution and strain partitioning of extensional faulting within the ~8 km wide Hayk-Ardibo marginal graben. A sub-horizontal minimum stress axis was identified orientated ENE-WSW/E-W using Andersonian dip slip faulting. The main deformation within the area is dominated by steeply dipping normal faults orientated NNW-SSE and N-S, which have dips ranging from 50 o to 75 o with some minor N-NE-SSW and WNW-SEE cross rift faults. Strain partitioning has resulted in significant asymmetric deformation. In the western flank of the graben deformation is concentrated along synthetic border fault (Wuchale Fault), which has large displacement values ranging from 900 m to 2,000 m. This produces a deep axial depocentre. The strain partitioning with in the graben resulting in a complex step-faulting system. Multiple basins have formed in this area (Alansha, Woldeluel and Ardibo). This has resulted in multiple basins with horst structures separating the basins. The stratigraphy shows that the faulting systems have cut through a volcanic sequence consisting of both the Ashenge and Dessie formations. Scarp profiles have shown that the area has progressed from initial border faulting to a more mature stage of deformation where strain has moved in to the graben. This research provides new insights into the partitioning and migration of extensional strain during continental lithosphere destruction.