Discriminating between pyroxenite and peridotite sources for continental flood basalts (CFB) in southern Africa using olivine chemistry

In addition, bulk rock geochemical data compilations and previously reported olivine δ18O for Karoo and Etendeka CFBs are discussed in order to further constrain source components based on previously described pyroxenite melt geochemical indices such as MgO-CaO systematics, FeO/MnO, Zn/Fe, and FC3MS (FeO/CaO-3*MgO/SiO2). These geochemical indices suggest a pyroxenite-dominated source for Karoo CFBs as well as for Etendeka ferropicrites whereas a peridotite-dominated source is indicated for Etendeka Horingbaai/LTZ-L type picrites analyzed in this study. Based on our data, Ni-enrichment of olivine in plume-related magmas in regions of thickened lithosphere in southern Africa is not ubiquitous. We therefore suggest that mineralogical variation of the source is a more likely major control of olivine chemistry and parent melt variations for Karoo and Etendeka CFBs. We also show that olivine Mn-Zn correlations are a useful discriminator for source variation and recommend the use of olivine Mn/Zn<13 for a pyroxenite-dominated source relative to olivine Mn/Zn>15 for a peridotite-dominated source.