Isotope Compositions of Submarine North Kona Tholeiitic Lavas, Hualalai Volcano, Hawaii

Four remote and manned submersible dives examined the deep submarine portion of the North Kona region, offshore Hualalai during 2001 and 2002 JAMSTEC cruises. The dives encountered compositionally homogeneous tholeiitic pillow lavas that are interpreted to have erupted from Hualalai during its shield stage. Hualalai volcano, the westernmost volcano on the Island of Hawaii is presently in the post-shield alkalic stage and most of its subaerial surface is covered by alkalic basalt. Difficulty accessing buried tholeiite is one reason that compositional data from the volumetrically dominant stage in the volcano's edifice are scarce. To identify source materials involved in shield stage of Hualalai can provide important information about the isotopic variation and evolution during Hawaiian volcano growth. We report the results of Hf, Pb, Sr, Nd isotopic compositions of 34 tholeiitic lava samples collected from submarine North Kona region. Hf, Nd, Sr isotopic compositions of the submarine North Kona lavas are similar to Mauna Loa tholeiites, and define a clear mixing line showing that the mantle source consists of at least two components. Some of new Pb isotopic data have higher 207Pb/204Pb and ^{208}Pb/204Pb, for a given 206Pb/204Pb, than published data from Mauna Loa and Hualalai. The trend emerges towards to 'Kea'-like component. Although in general Hawaiian basalts require more than two components to account for their geochemical variations, the isotopic variations in Hualalai shield lavas appear dominated by a mixture of two components: 'Koolau'-like enriched component and a 'Kea'-like depleted component, and contributed to relatively higher proportion of the 'Kea'-like component than the Mauna Loa.