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Abstract

The Red Sea—Gulf of Aden rift System provides a superb example of the formation of passive continental margins. Three phases are well represented: (1) continental rifting (Gulf of Suez); (2) rift-to-drift transition (northern Red Sea); and (3) sea-floor spreading (Gulf of Aden and southern Red Sea). Recently published radiometric and biostratigraphic ages, outcrop studies, and reflection seismic profiles more tightly constrain the evolution of this rift system. The principal driving force for separation of Arabia from Africa was slab-pull beneath the approaching Urumieh-Dokhtar volcanic arc on the north side of Neotethys. However, the rifting trigger was impingement of the Afar plume beneath northeast Africa at ~31 Ma. Rifting followed quickly thereafter, initiating in the Gulf of Aden, perhaps in the area between Socotra Island and southern Oman. Extension occurred in the central Gulf of Aden by ~29 Ma. Shortly thereafter, at ~27 Ma, rifting jumped to Eritrea, east of the Danakil region. Rifting then spread from Eritrea to Egypt at ~24 Ma, accompanied by a major dike-emplacement event that covered more than 2,000 km in possibly less than 1 Ma. At ~14 Ma, the Levant transform boundary formed, largely isolating the Gulf of Suez from later extension. Constriction of the Suez-Mediterranean and Red Sea-Aden marine connections resulted in widespread evaporite deposition at this time. Sea-floor spreading began in the eastern Gulf of Aden at ~19 Ma, the western Gulf of Aden at ~10 Ma, and in the south-central Red Sea at ~5 Ma. Propagation of the oceanic ridge has taken much longer than the propagation of its continental rift predecessor. Therefore, the rift-to-drift transition is diachronous and is not marked by a specific “breakup” unconformity. The Red Sea sub-basins are each structurally asymmetric during the syn-rift phase and this is seen in the geometries obtained when its present paired conjugate margins are palinspastically restored. During the Late Miocene and Pliocene, regional-scale, intrasalt detachment faulting, salt flowage, and mass-movement of the post-Miocene salt section toward the basin axis masked the deeper fault block geometry of most of the Red Sea basin. This young halokinesis has enormous consequences for hydrocarbon exploration.

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