A LREE-depleted component in the Afar plume: Further evidence from Quaternary Djibouti basalts

Major, trace element and isotopic (Sr, Nd, Pb) data and unspiked K-Ar ages are presented for Quaternary (0.90-0.95 Ma old) basalts from the Hayyabley volcano, Djibouti. These basalts are LREE-depleted (La-n/Sm-n = 0.76-0.83), with Sr-87/(86) Sr ratios ranging from 0.70369 to 0.70376, and rather homogeneous Nd-143/Nd-144 (epsilon(Nd) = +5.9-+7.3) and Pb isotopic compositions ((206)pb/Pb-204 = 18.47-18.55 Pb-207/Pb-204 = 15.52-15.57 Pb-208/Pb-204 = 38.62-38.77). They are very different from the underlying enriched Tadjoura Gulf basalts, and from the N-MORB erupted from the nascent oceanic ridges of the Red Sea and Gulf of Aden. Their compositions closely resemble those of (1) depleted Quaternary Manda Hararo basalts from the Afar depression in Ethiopia and (2) one Oligocene basalt from the Ethiopian Plateau trap series. Their trace element and Sr, Nd, Pb isotope systematics suggest the involvement of a discrete but minor LREE-depleted component, which is probably an intrinsic part of the Afar plume. (C) 2009 Elsevier B.V. All rights reserved.