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\ud 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\ud 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

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

“…1). Similar to other places along the EARS, the area shows significant recent and ongoing volcano-tectonic activity (Chernet, 2011;Corti et al, 2013;Philippon et al, 2014) and thermal emissions at the surface as springs and fumaroles (U.N. D.P., 1973;Craig et al, 1977;Chernet, 2011). The aim of the present study was to review the chemical and isotopic data of the thermal springs available in the literature, coupled with new data from field-work conducted in February 2015, during which freegas discharges and fumaroles, not previously analysed, were collected.…”

“…Under this perspective the study area is not an exception; most of the thermal springs discharge in low topographic areas along the Bilate River, whose SSW flow is constrained by the fault system bordering the rift (Corti et al, 2013). As described in the previous sections, apart from a restricted area at the western edge of the Chewkare graben (Fig.…”

“…The basalts are associated with the recent faults located in the western part of the rift valley, as documented by NNE-SSW alignments of numerous scoria cones (Fig. 2) marking the main fault swarms (Corti et al, 2013). The youngest episodes of basaltic eruptions are associated with the intense faulting that characterizes the margin in correspondence to the Hobitcha caldera.…”

“…The plan-view architecture of these faults is characterized by an array of sigmoidal, right-stepping en-echelon normal or oblique faults, indicative of oblique extension with respect to the roughly NE-SW-trending rift. Radiocarbon dating of faulted material pointed to significant Late Pleistocene-Holocene (post-30 ka) activity on these normal faults (Corti et al, 2013).…”

“…Field structural data indicate that the tectonic activity has played a major role in controlling the recent volcanism (Corti et al, 2013). East-dipping normal faults and their associated antithetic faults gave rise to minor grabens, within which the volcanic vents showed the highest density in the Salewa-Dore area (Fig.…”