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Discussion of ophiolites in Northeast and East Africa: implications for Proterozoic crustal growth

W. R. Church writes: In discussing the Pan-African geology of Northeast and East Africa, Berhe (1990) affirms that ophiolite decorated lineaments in the Arabian—Nubian Shield represent suture zones. The difference of opinion between Berhe (1990) and Stern et al. (1989) concerning the location of the supposed suture zones of northern Sudan and southern Egypt, is a clear illustration of the ambiguity that may arise through the uncritical use of this paradigm. Whereas Berhe considers the Sol Hamed—Wadi Onib ophiolite belt to represent in situ oceanic material located along a north—south trending extension of the Saudi Arabian Yanbu—Sol Hamed ‘suture’, Stern et al. 1989 link the latter with the east—west trending Allaqi—Heiani ophiolite belt, which they consider to be a major east—west suture ‘extending well into the interior of North Africa. This important difference in opinion is a clear indication of the arbitrary nature of suture selection based solely on the distribution of ophiolitic rocks. Furthermore, neither explanation may be correct.

The distribution of ophiolitic rocks in the southern part of the Eastern Desert and northern Sudan is more likely controlled by the southern Eastern Desert domal culmina­tion, out-of-sequence faulting, and the development of zones of intense ductile strain. Within the domal culmination, ophiolitic material exposed at lower structural levels near Abu Swayel, Gebel Nagy, Um Krush and perhaps Gebel Gerf, overlie highly deformed and metamorphosed pelitic metasediments containing a ‘con­tinental’ Nd isotope signature (Harris et al. 1984), quartzo-feldspathic gneisses (Umm Tundeiba), hornblende—cummin

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