Enriched components in the Hawaiian plume: Evidence from Kahoolawe Volcano, Hawaii

[1] The geochemical differences between individual Hawaiian shields provide clues to the magma source components in the Hawaiian plume. Lavas from Koolau (Makapuu-stage) and Kahoolawe volcanoes define the enriched, i.e., relatively high Sr/Sr and low Nd/Nd, extreme for Hawaiian shield lavas. There are, however, important geochemical differences between these shields; Kahoolawe lavas lack the relatively high SiO2, low CaO, and high Sr/Nb and La/Nb that are characteristic of Makapuu-stage Koolau lavas, and they are offset from other Hawaiian shield lavas to high Sr/Sr at a given Nd/Nd. Consequently, a varying role for recycled plagioclase-rich gabbro is inferred, in particular, lower amounts of the low Sr/Sr component in Kahoolawe lavas. Also, lavas from Loa-trend volcanoes, such as Kahoolawe, define trends ranging toward high Pb*/Pb* and Sr/Sr and low Nd/Nd and Hf/Hf. Such trends are consistent with variable amounts of recycled sediment sampled by Loa-trend volcanoes, with the largest proportion in Makapuu-stage Koolau lavas. Therefore the enriched component in the Hawaiian plume, the Koolau component, is recycled oceanic crust, which is heterogeneous because of varying proportions of sediment, basalt, and gabbro. Hawaiian shield-stage lavas range widely in Sr/Sr, Nd/Nd, Hf/Hf, and Pb/Pb, but they have similar ratios of Sr/Nd, Nd/Hf, and Hf/ Pb, each varying by a factor of <3 among the Hawaiian shields. This observation has important consequences. Namely, the similar Hf/Pb ratios are inconsistent with a two-component (i.e., Kea and Koolau) mixing model for explaining the hyperbolic trend of Hf/Hf versus Pb/Pb defined by shield lavas. Such a model requires end-members with very different Hf/Pb (a factor of 15 to 40), but this is not observed; therefore a third component must be involved. On the basis of trends of Pb*/Pb* versus Sr/Sr, Nd/Nd, and Hf/Hf, we infer that Loa and Kea trend shield lavas contain variable amounts of the Loihi source component. G Geochemistry Geophysics Geosystems