The Red Sea: A Newborn Ocean

During much of the Phanerozoic until the Oligocene, the African and Arabian plates were part of a single shield. The history of its dislocation via the Red Sea opening starts in the late Oligocene (~24 Ma), when the Arabian plate separated from that of Nubia through a rupture of the Precambrian shield and rotated counter-clockwise. After advanced continental rifting, oceanic spreading began in the Pliocene (~5 Ma) and continues to the present day, as demonstrated by the intense volcanic and seismic activity in the area during the last 10,000 years. Seafloor magnetic anomalies and normal faulting earthquakes, typically associated with spreading ridges, occur in the Red Sea south of 20°N, where a deep axial trough is present. To the north, only few isolated anomalies are identified, and the sea is floored by rotated fault blocks. South of 16°N the axial trough narrows and some groups of islands emerge, the last of which was formed in 2013 in the Zubair Archipelago. The northern area is interpreted as continental crust being stretched and faulted with only minor volcanic activity, whereas the southern area has evolved to the point that new lithosphere is being produced at a spreading axis. This situation has been viewed as transient until the extension in the northern area evolves into seafloor spreading. The southern deep axial trough is the focus of intense submarine volcanic activity. The geochemistry of erupted magmas conveys valuable information about the underlying mantle. They are low potassium tholeiitic basalts with K2O < 0.2% and TiO2 < 2.0%. Their Sr and Nd isotope ratios are ? 0.703 and ? 0.513, respectively. These geochemical features are typical of mid ocean ridge basalts (MORB), and allow the Red Sea to be regarded as a newborn ocean, whose development likely resembles that of the Atlantic Ocean in its early stages, and which may one day become the sixth ocean of the planet. It is interesting to note that the erupted lavas are characterized by geochemical variations along the Red Sea. The basalts of the central part exhibit geochemical parameters that resemble those of MORB. Both north and south, the basalts display higher contents of incompatible elements, higher Sr and lower Nd isotope ratios, as well as higher Pb isotopes (206Pb/204Pb up to 19.608), than those recorded in the central part, suggesting a contribution by "enriched" mantle components.