The Afar Depression: transition between continental rifting and sea-floor spreading

Abstract

Abstract Detailed geophysical and geological studies were undertaken in the 1970's in the Afar Depression, Ethiopia, in order to study the processes of continental break-up occurring in this unique setting; the Afar is located between the Ethiopian and Somali Plateaus and the Red Sea. We have re-evaluated the available seismic refraction and gravity data using modern interpretation techniques and incorporated new information derived from magnetic, gravity, seismicity and seismic refraction data. The results of the re-evaluation indicate that the Afar Depression is a transition zone between the continental rifts of Kenya and the present ongoing sea-floor spreading of the Red Sea and the Gulf of Aden. In the Depression itself the crust is greatly attenuated and is underlain by a low velocity (7.4–7.5 km/s), high temperature upper mantle material. However, it is still a continental crust which thins to the northeast and east towards the Red Sea and the Gulf of Aden. It is not a newly formed oceanic crust as has been suggested in the past. The trends of the areas of crustal thinning are indicated by the gravity anomalies. The trend of the Ethiopian Rift reaches South Afar where the trend of crustal thinning changes and becomes parallel to the Red Sea trend. It is offset en echelon from the spreading area of the Red Sea, which is marked by an alignment of gravity maxima. The Gulf of Aden trend continues west towards the Ethiopian Rift. The gravity trends coincide with areas of maximum crustal thinning and may thus suggest a possible triple junction in development.