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