Geology of Ethiopia: A Review and Geomorphological Perspectives

Abstract

The Ethiopian region records about one billion years of geological history. The first event was the closure of the Mozambique ocean between West and East Gondwana with the development of the Ethiopian basement ranging in age from 880 to 550 Ma. This folded and tilted Proterozoic basement underwent intense erosion, which lasted one hundred million years, and destroyed any relief of the Precambrian orogen. Ordovician to Silurian fluviatile sediments and Late Carboniferous to Early Permian glacial deposits were laid down above an Early Paleozoic planation surface. The beginning of the breakup of Gondwana gave rise to the Jurassic flooding of the Horn of Africa with a marine transgression from the Paleotethys and the Indian/Madagascar nascent ocean. After this Jurassic transgression and deposition of Cretaceous continental deposits, the Ethiopian region was an exposed land for a period of about seventy million years during which a new important peneplanation surface developed. Concomitant with the first phase of the rifting of the Afro/Arabian plate, a prolific outpouring of the trap flood basalts took place predominantly during the Oligocene over a peneplained land surface of modest elevation. In the northern Ethiopian plateau, huge Miocene shield volcanoes were superimposed on the flood basalts. Following the end of the Oligocene, the volcanism shifted toward the Afar depression, which was experiencing a progressive stretching, and successively moved between the southern Ethiopian plateau and the Somali plateau in correspondence with the formation of the Main Ethiopian Rift (MER). The detachment of the Danakil block and Arabian subcontinent from the Nubian plate resulted in steep marginal escarpments marked by flexure and elongated sedimentary basins. Additional basins developed in the Afar depression and MER in connection with new phases of stretching. Many of these basins have yielded human remains crucial for reconstructing the first stages of human evolution. A full triple junction was achieved in the Early Pliocene when the MER penetrated into the Afar region, where the Gulf of Aden and the Red Sea rifts were already moving toward a connection via the volcanic ranges of northern Afar. The present-day morphology of Ethiopia is linked to the formation of the Afar depression, MER, and Ethiopian plateaus. These events are linked to the impingement of one or more mantle plumes under the Afro-Arabian plate. The elevated topography of the Ethiopian plateaus is the result of profuse volcanic accumulation and successive uplift. This new highland structure brought about a reorganization of the East Africa river network and a drastic change in the atmospheric circulation.

What Drives the Lateral Versus Vertical Propagation of Dikes? Insights From Analogue Models

“…In nature, the rigidity decrease with depth, leading to rigidity inversions (i.e., stiff layer above a weak one, as we modeled here), may be due to soft scoria layers capped by stiff lava flows, as in Afar (Abbate et al, ) and Iceland (A. Gudmundsson, ). Moreover, at a broader scale, partial melt or superheated steam in geothermal areas decreases the rigidity of the host rock by thermal weakening (Heap et al, ), so that it becomes more compliant at high depths, as geophysically detected at Askja and Krafla (Iceland; Mitchell et al, ; Schuler et al, ), Kilauea's East Rift Zone (Hawaii; Haslinger et al, ), Afar (Desissa et al, ), and Canary Islands (Martí et al, ).…”

Control of Pre‐rift Lithospheric Structure on the Architecture and Evolution of Continental Rifts: Insights From the Main Ethiopian Rift, East Africa

“…Several tectonic events affected Ethiopia prior to the Cenozoic rifting, from collision during the Precambrian to Mesozoic extension (Abbate et al, , and references therein). This long pre‐Cenozoic history of tectonic events created pre‐existing heterogeneities with variable orientation that have controlled the development of the East African Rift System in Ethiopia (e.g., Korme et al, ).…”

“…In this contribution, we integrate detailed geological‐structural and geomorphological analysis to investigate the along‐axis variations in architecture, segmentation, and evolution of the different rift sectors of the Main Ethiopian Rift (MER), East Africa, and relate these characteristics to the lithospheric structure and surface processes. The MER is a classical example of continental rifting developed within a highly anisotropic lithosphere that has experienced several tectonic events over the last one billion years of geological history and tectonics (e.g., Abbate, Bruni, & Sagri, and references therein). It is an ideal study locale for the analysis of rift structure in conjunction with surface processes since the expression of different stages in the evolutionary rift sequence, from initial rifting in the south to incipient breakup in the north, are all subaerially exposed and rigorously studied at depth using geophysical techniques (e.g., Corti, ; Ebinger et al, ; Keir et al, ).…”

Effects of River Capture and Sediment Flux on the Evolution of Plateaus: Insights From Numerical Modeling and River Profile Analysis in the Upper Blue Nile Catchment

“…The preeruption topography was affected by domal uplift of ~1,000 m maximum in the Afar region produced by the upwelling of the African superplume (Mohr, ; Moucha & Forte, ; Sengor, ; Sembroni, Faccenna, et al, ). The domal uplift encompassing the Ethiopian Plateau and surrounding areas started during the Eocene and the crustal warping produced fissures that fed the Oligocene flood basalts (Abbate et al, ; Dainelli, ; Mohr, ). The large‐scale doming of the Ethiopian Plateau continued even after the massive eruption of the flood basalts as a dynamically supported process that is probably still active (Sembroni, Faccenna, et al, ).…”