Timing of Extensional Faulting Along the Magma-Poor Central and Northern Red Sea Rift Margin—Transition from Regional Extension to Necking Along a Hyperextended Rifted Margin

Abstract

In light of voluminous Oligocene continental flood basalts in the Afar/Ethiopian region, the Red Sea has often been viewed as a typical volcanic rift, despite evidence for asymmetric extension and hyperextended crust (Zabargad Island). An in-depth analysis of the timing, spatial distribution, and nature of Red Sea volcanism and its relationship to late Cenozoic extensional faulting should shed light on some of the misconceptions. Voluminous Eocene to Oligocene flood basalts in northern Ethiopia and western Yemen at ~31–30 Ma were synchronous with the onset of continental extension in the Gulf of Aden, but demonstrably predate Red Sea extensional faulting and rifting. Basaltic dike emplacement, syn-rift subsidence and sedimentation, and rapid rift-related fault block exhumation at ~23 Ma along the entire Red Sea-Gulf of Suez rift system mark the onset of Red Sea rifting. Early Miocene rifting affected a wide area (~1200 km) around the northern Red Sea with limited strain localization along the main rift axis between ~20 and 14 Ma. While the initiation of lithospheric extension in the northern and central Red Sea and Gulf of Suez was accompanied by only sparse basaltic volcanism and possible underplating, the main phase of rifting in the Miocene Red Sea/Gulf of Suez lacks significant rift-related volcanism. There appears to be no evidence for the formation of SDRs or accretion of a thick proto-oceanic crust. Rift localization and major crustal thinning continued throughout the Early Miocene. Middle Miocene onset of left-lateral displacement along the Gulf of Aqaba transform resulted in the tectonic isolation of the Gulf of Suez and a switch from rift-normal to highly oblique extension with the Red Sea. Oblique extension led to the formation of fracture zones, pull-apart basins, and crustal necking, and ultimately local crustal separation and mantle exhumation, prior to Plio-Pleistocene incipient oceanic breakup in the northern Red Sea. This clearly supports the interpretation of the northern Red Sea as a magma-poor rift system and the importance of the Middle Miocene kinematic reorganization for continental breakup.