ISOTOPIC CHARACTERISTICS OF INTRAPLATE BASALTS IN WEST PACIFIC

Most of the West Pacific intraplate basalts are the products of Mesozoic intraplate volcanisms in the South Pacific. The comparison made for the intraplate basalts in the West and South Pacific may reveal the characteristics and the evolution of the super plume in the South Pacific. Based on the previous data published on basalts in the West and South Pacific, we made a study of Sr-Nd-Pb isotopic geochemistry and compared the results from the two regions. The results show that: 1) The isotopic composition of the West Pacific intraplate basalts shows a great heterogeneity, almost covering all the enriched mantle end members, while most of the West Pacific intraplate basalts are the mixture of HIMU and EM-1; 2) Compared to the South Pacific, the isotopic composition of the West Pacific intraplate basalts is less extreme, which indicates a more thorough mixing between mantle end members; 3) Since ~120 Ma, the HIMU-type of basalts are continuous, while EM1-type and EM2-type basalts are intermittent, which may imply that the spatial distribution of HIMU is different from other enriched end members in the deep mantle.