QUATERNARY VOLCANIC ACTIVITY OF THE SOUTHERN RED-SEA - NEW DATA AND ASSESSMENT OF MODELS ON MAGMA SOURCES AND AFAR PLUME LITHOSPHERE INTERACTION

Chemical compositions and Sr-Nd-Pb isotopic ratios are reported for Qu aternary alkaline volcanic rocks from the southern Red Sea and adjacen t regions. Samples from the Ramad seamount (17 degrees N) have highly radiogenic Pb isotope ratios (Pb-206/Pb-204 = 19.59-19.61) and compara tively depleted Sr and Nd signatures. In isotope diagrams the samples from this seamount fall on extensions of linear arrays defined by samp les of Red Sea N-type and E-MORB and confirm the existence of an impor tant HIMU-type component in the mantle beneath the southern Red Sea. A lkali basalts from the islands of Hanish and Zubair located in the sou thernmost part of the Red Sea do not lie on isotope mixing lines defin ed by Red Sea MORE and Ramad seamount samples. Instead, their data poi nts are shifted towards the data field of Quaternary Afar and Yemen vo lcanic rocks, thus reflecting the presence of a third isotopic compone nt with hybrid EM1-EM2 characteristics which dominates the continental volcanic rocks on both shoulders of the southernmost Red Sea. The sys tematic covariation of isotope ratios and geographic position in south ern Red Sea volcanic rocks are very similar to those observed along th e Gulf of Aden and thus support the torus plume model proposed by Schi lling et al.