Structural controls on the emplacement of scoria cones and rhyolite domes of the western Afar margin, Ethiopia

Matured continental rift zones that imprint the complete cycle of rifting are rare deformation environments in the globe. The western Afar margin is one that shows such a complete process. This research is aimed to understand the development of the lower part of the western Afar margin and determine the nature of transfer zones that host the mega dike injections, the elliptical scoria cones, and rhyolitic domes around Gulina area. To do so, structural analyses were conducted using intensive field measurements, Landsat ETM+, and SPOT imageries, and digital elevation models (DEM) data to comprehend chronologically distinct structures and magmatic series. The result shows that marginal structures are represented by older rift bounding NNW-SSE trending faults and younger NE-SW oriented transverse structures. Mode of emplacement of these two structurally and chronologically distinct structures are found associated with the evolution of the marginal magmatic series. The study has also investigated NE-SW trending offset faults and NE-SW striking transversal structures. Moreover, this work shows that the marginal structures are inactive but the younger structures (mega dikes and scoria cones are active and controlled by regional transversal structures that separate the Erta’Ale range and Tendaho-MandaHararo rift segment). From the recognition of the cross-cutting relationship, the marginal faults are identified as firstgeneration fractures, whereas the deformed domical silicified rhyolite outcrops situated in the marginal areas are classified under the second generation. The preserved rhyolite dome in the rift floor, the scoria cones, rift floor fractures, and dikes are found to be third-generation structures.