Geochemical characteristics of Icelandic basalts require mixing of several sources: depleted asthenosphere, a plume (presumably heterogeneous), and an enriched component (e.g. hydrothermally altered crust). We use lava compositions and Sr-Nd-Pb isotopic ratios from neighbouring coeval volcanic centres to define spatial variations in source components beneath the neovolcanic zones. Within the Eastern Volcanic Zone, basalt compositions vary systematically from tholeiitic near central Iceland (Veidivotn, Grimsvotn) to Fe-Ti tholeiites at Hekla and Katla, to alkaline in Vestmannaeyjar. Each volcanic centre has distinctive geochemical characteristics that require differences in source components and proportions on the scale of 10–20 km.