A Chemical and Multi-Isotope Study of the Western Cape Olivine Melilitite Province, South Africa: Implications for the Sources of Kimberlites and the Origin of the HIMU Signature in Africa

explain the isotopic variations of Group 1 kimberlites, but the We present major and trace element and Sr–Nd–Pb–Hf–Os isotopic available data do not allow us to rule out a major role for convecting data for the 76–58 Ma Western Cape melilitite province, an agemantle components in kimberlite genesis. Using the Western Cape progressive magmatic lineation in which primitive olivine melilitite melilitites as an analog, we propose a model in which the strong intrusives and alkali basalt lavas have been emplaced on the HIMU isotopic signature present in most Late Cretaceous to Recent southwestern margin of South Africa. The magmas range from alkaline magmatic provinces across Africa is supplied not by alkali basalts with strong HIMU isotopic and trace element affinities conventional mantle plumes, but rather by pods of recycled oceanic on the continental shelf to melilitites with kimberlite-like incompatible crust brought up from the deep mantle within a long-lived, and element compositions and EM 1 isotopic affinities on thick Protlaterally broad mantle upwelling feature located beneath the African erozoic lithosphere (i.e. Sr/Sri = 0·7029–0·7043, Nd(t) = plate. +5 to +2, Pb/Pbi = 20·5–18·1). The samples are characterized by radiogenic Os/Osi (0·15–0·21) and unradiogenic Hf isotope ratios, causing some of them to fall outside the compositional range of oceanic basalts. This suggests that they