Similarities in rock assemblages and facilitated thrust stacks of juvenile assemblages broad tectonic features between the late Precam-to override the ancient cratonic edge that may now brian to early Paleozoic basement of Arabia, the be buried beneath the SE Desert of Egypt. models that were proposed for Arabia, although at of Egypt and in Arabia, and they supported the least 2 of the Nubian ophiolite belts clearly con-arc accretion model developed for these regions. tinue into the Arabian shield. Subsequently Vail (1976) attempted to integrate The Pan-African structural domain with low-angle the Red Sea Hills into the geology of the entire thrusts and ophiolite m•langes extends at least as Arabian-Nubian shield and suggested that the far W as the River Nile, where the ancient margin "greenschist assemblages" were part of the same of the African craton may be found, The entire Pan-African crustal domain as the Eastern Desert domain farther E is characterized by newly accre-of Egypt and the Arabian basement, while he conted magmatic associations of late Precambrian age sidered the high-grade gneisses at the River Nile that may have evolved in settings similar to those to represent the edge of the ancient African crapresently observed in the Indonesian archipelago. ton. Further work led to a first evolutionary (]976) were the first to recognize the similarity these rocks is revealed by the local presence of of rock types and their tectonic settings in the sillimanite, while primary sedimentary structures NE Red Sea Hills with those in the Eastern Desert were largely destroyed by intense deformation and 236 KRONER ET AL.

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The location and geometry of a rift are controlled by some combination of the extensional stress field and preexisting lithospheric structures, unless the lithosphere is perfectly homogeneous. However, the nature and location of these structures may be difficult to identify because of subsidence and sedimentation associated with later rift stages. Two regional north trending Precambrian structures in northeast Africa have been identified that may have influenced the late Cretaceous and Tertiary evolution of the Red Sea. A large (300 km north‐south, 50 km east‐west) structure in northeastern Sudan (the Onib‐Hamisana zone) may be either a late Precambrian suture zone or a zone of transcurrent faulting. Highly deformed island arc and oceanic assemblages as well as associated ultramafic rocks occur throughout the zone. In one locality the arc assemblages are juxtaposed against possible continental margin metasedimentary rocks. To the southeast, on the Sudan‐Ethiopia border, a zone of similar size and orientation occurs and has been termed the Baraka suture zone. Offsets in the trend of the Red Sea coastline and axial trough coincide with both the location and spacing of the Onib‐Hamisana and Baraka zones. That part of the Red Sea immediately adjacent to the Baraka zone also coincides with a seismically active area. We present a model relating these preexisting lithospheric structures, which act as weak zones or stress guides, to the subsequent evolution and geometry of the rift. The rift propagation direction (northwest) is assumed to be perpendicular to regional extensional stress until the rift tip intersects a north trending stress guide at some arbitrary point. Rift propagation then proceeds northward until the zone ends or becomes poorly defined, whereupon northwest propagation resumes. In the resulting plate configuration, the guiding weak zones are observed only on the southwest plate.