Differences between oceanic basalts by multitrace element ratio topology

Trace element multidimensional analysis of ocean island basalts defines a structure delimited by the same four end members (Hawaiian Islands, St. Helena-Tubuai-Mangaia Islands, Kerguelen-Gough-Tristan da Cunha and the Society Islands) as determined by isotope ratios. In contrast to the results obtained for the distribution of isotopic ratios, the dispersions of trace element concentrations in mid-ocean ridge basalts are greater than those for ocean island basalts. This can be accounted for by a two-component mantle source composed of pyroxenite layers embedded in a peridotitic matrix, which melts to varying degrees; ocean island basalts are produced by a relatively uniform low degree of melting of the pyroxenite and limited isotopic exchange with the surrounding matrix, whereas mid-ocean ridge basalts are melts of both components with higher and more variable extents of melting and complete isotopic exchange between the pyroxenite strips and the peridotitic matrix.