Quaternary volcano‐tectonic activity in the Soddo region, western margin of the Southern Main Ethiopian Rift

Abstract

We present an analysis of the distribution, timing, and characteristics of the volcano‐tectonic activity on the western margin of the Southern Main Ethiopian Rift in the Soddo area (latitudes between ~7°10'N and ~6°30'N). The margin is characterized by the presence of numerous normal faults, with limited vertical offset and often sigmoidal in shape, which accommodate a gentle transition from the rift floor to the Ethiopian plateau. New radiocarbon dating indicates post‐30 ka fault activity, pointing to a significant Late Pleistocene‐Holocene tectonic activity of the Soddo margin. Comparison of the fault architecture with analog models suggests that deformation has been controlled by a sub‐E‐W (roughly N100°E) extension direction, resulting in an oblique extension with respect to the roughly NE‐SW‐trending rift. This well accords with inversion of fault slip data collected on faults with Pleistocene‐Holocene activity and is also in good agreement with recent GPS data from the Southern Main Ethiopian Rift. Our data support a close correlation between the recent volcanic activity and deformation in the study area, with eruptive vents located along the recent border faults; the axial tectono‐magmatic activity is subordinate in the area. These findings support a transition from axial tectono‐magmatic deformation in the Northern Main Ethiopian Rift to marginal deformation in the Central and Southern Main Ethiopian Rift, in turn indicating an along‐axis, north to south decrease in rift maturity.