Constraining the Opening of the Red Sea: Evidence from the Neoproterozoic Margins and Cenozoic Magmatism for a Volcanic Rifted Margin

Abstract

As the Earth’s best-known example of an active, incipient ocean basin, the Red Sea provides crucial information about continental rifting and the tectonic transition from extended continental crust to seafloor spreading. Study of the Red Sea over the past decades has given many answers, but significant questions remain about how and when it opened because of lacking or ambiguous data and thick salt cover. A key issue is the geometry of the pre-rift join between the Arabian and Nubian Shields that form the basement flanking the Red Sea because this constrains the nature of Red Sea crust. The Neoproterozoic basement rocks flanking the Red Sea contain prominent shears and sutures between amalgamated tectonostratigraphic terranes, regions of transpressional shortening, and brittle-ductile faults related to Ediacaran orogenic collapse and tectonic escape. These structures vary in orientation from orthogonal to oblique with respect to the Red Sea coastlines. Importantly, they correlate across the Red Sea, and provide piercing points for a near coast-to-coast palinspastic reconstruction of the Arabian and Nubian Plates along the entire Red Sea. A tight pre-rift fit of the Arabian and Nubian Shields implies that most of the Red Sea is underlain by oceanic crust. Potential-field data are compelling evidence for oceanic crust along the axis of the Red Sea south of latitude ~22°N, persuasive for the margins of the southern Red Sea, and suggestive for the northern Red Sea. A variety of 20–24 Ma dikes, gabbros, and basaltic flows emplaced during the early stages of Red Sea rifting are consistent with Miocene asthenospheric upwelling, partial melting, and intrusion that would have weakened and facilitated rupture of the ~40-km thick continental crust and thicker mantle lithosphere of the then contiguous Arabian and Nubian Shields. The dikes, gabbros, and basaltic flows emplaced during the early stages of Red Sea rifting are strong evidence furthermore that the Red Sea is an example of a volcanic-rifted margin. Offshore seismic profiling designed to image beneath the salt followed by drilling to basement in the Red Sea are required to test these ideas.