CONTINENTAL BREAK-UP IN A PLUME PROVINCE: INSIGHTS FROM THE SOUTHERN RED SEA

Continental breakup involves the localisation of strain to a narrow zone along which seafloor spreading commences. The asymmetry of conjugate passive margins has led many to propose that these high strain zones are crustal- or lithospheric-scale detachments until breakup. We propose a new model for continental breakup in regions with a ready magma supply, based on observations from the southern Red Sea margins in Yemen and Ethiopia. During early rifting stages, border faults accommodate most of the strain across the rift. During the late stages of continental rifting, extensional strain migrates to a zone of dike injection and faulting within the rift, and the border fault is largely abandoned. These magmatic segments are similar to those found along slow-spreading mid-ocean ridges. Strain across much of the Afar depression on the western side of the Red Sea is localised in these magmatic segments. We also discovered early Miocene magmatic segments along the Ethiopian margin of the Red Sea that are exposed by ongoing extension. Volcanic strata in these Miocene magmatic segments show seaward dips >30^o, analogous to seaward-dipping reflector sequences (SDRs) found on other passive margins. Our field, geomorphology, and geochronology studies, and plate reconstructions imply that some SDRs form on continental crust during the late syn-rift stages.