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Prior to the formation of the Red Sea the northeastern Afro/Arabian continent had low relief and was largely below sea level from the Late Cretaceous to the early Oligocene. The events leading to the formation of the Red Sea followed the sequence (1) alkaline volcanism and rifting beginning about 30–32 Ma affecting a narrow linear zone in the continent, (2) rotational block faulting and detachment faulting, well underway by 25 Ma, (3) gabbro and diorite magmatism, andesite to rhyolite volcanism, and fine‐grained nonmarine sedimentation in the rift between 20 and 25 Ma, (4) fine‐grained marine sedimentation in the rift as the early shelves started to subside in the middle Miocene, and (5) uplift of the adjacent continents (about 3 km) and subsidence of the shelves (about 4 km) between 13.8 and 5 Ma. The youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the Proterozoic Arabian Shield that range in age from 13.8 to 568 Ma. The youngest of these ages, coupled with the present high relief along the Arabian escarpment and published heat flow measurements, indicate that 2.5–4 km uplift has occurred in the last 13.8 m.y. The sequence volcanism/rifting followed by uplift leads to our adoption of a passive mantle model for rift origin. Models that require uplift to create the rift are rejected, because of the late uplift. We advocate a model of lithospheric extension caused by two‐dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere. It is acknowledged that traction models could explain the observed data, but they imply a rigid, static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions. Neither requirement is necessary in the extension model. The rift starts with mechanical extension in a narrow zone of lithosphere between 25–32 Ma in our model. The thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift. Ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis. Once partially melted, rocks formerly part of the continental lithosphere join the upwelling asthenosphere, resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge. The resulting density decrease explains the uplift. We think that the Red Sea began as a consequence of changing plate geometries resulting from the collision of India and Eurasia. After the collision, the segment of the Owens fracture zone north of the Carlsberg Ridge became locked, forcing the northeast corner of Afro/Arabia to rotate with the Indian plate away from the rest of Africa.

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The Blue Ridge escarpment is a rugged landform situated within the ancient Appalachian orogen. While similar in some respects to the great escarpments along other passive margins, which have evolved by erosion following rifting, its youthful topographic expression has inspired proposals of Cenozoic tectonic rejuvenation in eastern North America.To better understand the post-orogenic and post-rift geomorphic evolution of passive margins, we have examined the origin of this landform using low-temperature thermochronometry and manipulation of topographic indices. Apatite (UT h)/He and ¢ssion-track analyses along transects across the escarpment reveal a younging trend towards the coast.This pattern is consistent with other great escarpments and ¢ts with an interpretation of having evolved by prolonged erosion, without the requirement of tectonic rejuvenation. Measured ages are also comparable speci¢cally to those measured along other great escarpments that are as much as 100 Myr younger.This suggests that erosional mechanisms that maintain rugged escarpments in the early post-rift stages may remain active on ancient passive margins for prolonged periods.The precise erosional evolution of the escarpment is less clear, however, and several end-member models can explain the data. Our preferred model, which ¢ts with all data, involves a signi¢cant degree of erosional escarpment retreat in the Cenozoic. Although this suggests that early onset of topographic stability is not required of passive margin evolution, more data are required to better constrain the details of the escarpment's development.