14. Ring Intrusion, Jebel Uwaynat, Sudan/Egypt/Libya
Circular structures are always eye-catching from space since they are such unusual features of the terrestrial landscape. In this respect, the Earth is quite different from all the other terrestrial planets and satellites, on which circular impact structures are by far the most common (and sometimes the only) surface features. This elliptical feature forms the Jebel Uwaynat on the triple point of Sudan, Egypt, and Libya (the topographic feature was used to define the geographic point). The structure is the surface expression of an ancient granite intrusion intruded into the Precambrian metamorphic basement along elliptical ring fractures. The granite is clearly more resistant to erosion than the basement it intrudes, which is mantled by the sand sea of the Sahara. Structures of this sort are common in Sudan and Egypt; they were formed 600 — 700 million years ago during the so-called pan-African event, which affected much of North Africa. Little is known in detail about the Uwaynat structure, which has rarely been visited by geologists. (Uwaynat is spelled various ways, including Aouenat.)
STS-41D, August-September 1984. Picture #14-34-017.