Large coastline gaps in Red Sea palinspastic reconstructions are not tenable if interpretations of seismic refraction data from the continental margin of southwest Saudi Arabia in the southern Red Sea typify the crustal configuration of most of the basin. The composition of the crust beneath 4–6 km of shelf and coastal-plain sediment is not certain. Ely assuming (1) that it is extended continental crust that could be reorganized in a kinematically reconstructed cross section of the prerift continent, the minimum possible divergence between the stable parts of Africa and Arabia can be determined. The maximum divergence is derived by assuming (2) that the crust formed from a mantle source by rift-related igneous processes (i.e., “oceanic” crust). Such crust would disappear during the reconstruction. Assumption 1 suggests that the widest possible shoreline gap was 30 km at lat 17°N, corresponding to a minimum divergence of about 320 km. The Arabian and African shorelines would overlap by at least 25–40 km if assumption 2 is used. This suggests a maximum divergence of about 380 km. The buried rocks are probably a mixture of continental and oceanic types; thus some amount of coastline overlap is desirable in tectonic reconstructions of the early Afro-Arabian continent.

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