Topographic and volcanic asymmetry around the Red Sea: Constraints on rift models

Abstract

The Red Sea rift is asymmetric, with the locus of uplift and Tertiary volcanism in Saudi Arabia, 200–400 km east of the present rift axis. One model for this asymmetry involves simple shear extension on an east dipping, low‐angle master fault that penetrates the lithosphere. Uplift and volcanism would mark the location where the fault enters the asthenosphere. However, observed seismicity, regional heat flow, and sedimentation are not in accord with this model's predictions. An alternate model involves interaction of upwelling asthenosphere in the early rifting stage with a nearby crustal weak zone such as a suture that controls rift location. In general, the location of the weak zone and subsequent rift will not coincide with the locus of mantle upwelling, leading to several asymmetric rift features. In this model, Tertiary volcanism in Saudi Arabia marks the location of initial upwelling, and uplift is due to crustal thickening associated with magmatic underplating and crustal intrusion. The incipient crustal rift and the locus of mantle upwelling will tend to align as rifting continues and stable seafloor spreading develops, implying relative migration of the lithosphere and asthenosphere. Absolute plate motion models for Africa and strongly asymmetric spreading in the Red Sea are consistent with northeast migration of the incipient rift and adjacent lithosphere with respect to a zone of asthenospheric upwelling.