PULL‐APART EVOLUTION OF THE RED SEA

Abstract

The Authors have deduced from seismic, gravity and other geophysical data that strike‐slip processes mainly controlled the early break‐up stages of the Arabian Plate from Africa, initiating the Red Sea Rift. Sea‐floor spreading is only 5 million yrs old, and is still limited in the central and parts of the southern Red Sea. The area was a zone of structural weakness as early as 600 million yrs ago, and was reactivated in the late Oligocene with intense magmatic activity and the development of a continental rift.Wrench‐faulting shaped most of its western flank as a sharp plate boundary, while the eastern flank is floored by stretched continental crust due to uplifting and shifting of Arabia from Africa. Wrench‐faulting was controlled by pre‐existing fault systems, such as the Najd Shear System, the Central African Fault Zone, or the Onib‐Hamisana and Baraka sutures. As a consequence, both wrench‐faulted transtensional and transpressional areas developed. Transtensional basins are evident offshore Egypt, the Sudan and the Gulf of Aqaba; while the island of Zabargad is a remnant transpressional area.With Arabia as the “mobile” plate and Africa relatively “stable”, the eastern Red Sea flank was formed through stretching, thinning and diffuse extension, and is floored by attenuated continental crust, thus producing the asymmetry observed in seismic sections between the eastern and western flanks of the Red Sea Rift. The Dead Sea strike‐slip fault only experienced intense deformation during the last 14 million yrs. Plate motion was oblique to the initial orientation of the basin, and could no longer be accommodated by the opening of the Gulf of Suez; the en échelon distribution of gravity and magnetic anomalies as well as the high heat‐flow fields recorded in the northern Red Sea are Gulf of Aqaba oriented due to this process. Similarly, the thinned continental crust between Yemen and Ethiopia is affected by shear‐faults that displace the volcanic centres to the east.The bathymetry reflects the tectonic processes described above, and the mineralisation in the metalliferous “deeps” is tied either to Recent sea‐floor spreading centres or to the en‐échelon distributed fractures along the Red Sea flanks. Sedimentary basins, aligned along the stretched continental, flanks of the Red Sea, are important for oil and gas exploration.