Mantle heterogeneity in the North Atlantic : evidence from oceanic islands

International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.Geochemical domains in the North Atlantic have been based upon major element composition of island basalts such as the K/Na-ratio with potassic islands such as São Miguel (Azores) distinguished from highly sodic provinces (Madeira group) (Schmincke, 1973): - ocean floor basalt glasses from the Mid-Atlantic Ridge with Ti-rich and K-poor provinces, south of ca. 32° N, distinguished from areas richer in K (north of ca. 32° N) (Melson, Dimitriev, 1979); - highly incompatible elements such as Th and La which show characteristic ratios for several ocean floor provinces in the northern North Atlantic (Tarney, Treuil, Wood, 1979). […].