Geochemical evolution of mantle sources during continental rifting: the volcanism of the Red Sea

Rift formation is a crucial topic in global tectonics. The Red Sea is part of the Afro-Arabian rift system, the world's largest active continental rift system. It is an exemplary case of a young rifting process that developed shortly after the arrival of a mantle plume at shallow depth, i.e. the Afar triangle. The mantle plume signature was indicated by the Ethiopian-Yemeni continental flood basalt sequences in the Late Eocene to Middle Miocene. The onset of continental rifting began ~22 Ma ago and encompassed the whole length of the present-day Red Sea basin and Gulf of Aden. The oceanic stage of the Red Sea, associated with the onset of seafloor spreading and production of oceanic crust, started about 5 Ma ago. In the late Oligocene-early Miocene up to the present time, large volumes of flood basalts emplaced at discrete eruptive centres along the western margin of the Arabian plate from the Gulf of Aden to the Mediterranean area. These plateau basalts are concentrated on the Arabian side of the Red Sea without matching counterparts on the Nubian plate, and represent one of the largest areas worldwide of predominantly alkali-olivine basalts.Basaltic rocks from the Red Sea display systematic along-axis geochemical and isotope variation patterns. In the central Red Sea basin, associated with the current mid-ocean ridge, a N-MORB mantle component is prevalent. In both northern and southern sectors of the basin, basalts determined a mixing trend between a depleted component and a reservoir with prevailing HIMU component. The strongest HIMU signature is present at 17°N, where the site of the initial spreading is set. The sub-aerial magmas from the southern restricted extremity of the trough, along with continental flood basalts from the Cenozoic Yemen Volcanic Province, defined a mixing trend between N-MORB and a reservoir with dominant EM (I+II) component, geochemically and isotopically similar to the Arabia Lithospheric Mantle.The geographical distribution of geochemical signatures is mostly consistent with a narrow mantle plume controlled by direct flow of asthenosphere beneath a pre-existing flexure in the continental lithosphere. The main asthenospheric source for the Red Sea volcanism lies eccentric to its axis and coincident with a north-south thermal line. At the place of initial seafloor spreading, 17°N, basalts show the strongest HIMU signature. From there, symmetric rift propagation, both northward and southward, away from the maximum mantle upwelling, is reflected by symmetricdecreasing of the HIMU signature. Interaction with lithospheric mantle in both southern and northern restricted extremity of the trough produced the EM signature to the north (basalts from 25 to 26°N), to the south (the volcanic islands) and in the Yemen continental flood basalts