Geochemical constraints on the role of oceanic lithosphere in intra-volcano heterogeneity at West Maui, Hawaii

Stratigraphically well-constrained sequences of late shield-building stage lavas from West Maui volcano, Hawaii, show age-dependent compositional variability distinct from that seen in shield-stage lavas from any other Hawaiian volcano. These distinctions are defined by Pb-206/Pb-204-Pb-208/Pb-204 variation as well as Sr-87/Sr-86 correlation with Pb-206/Pb-204 and trace element compositions. ne West Maul lavas from stratigraphically higher in the sequence have major and trace element and Sr-Pb-Hf-Nd isotopic compositions similar to Kea-type lavas sampled at the younger Mauna Kea and Kilauea volcanoes, indicating that the Kea compositional end-member Of Hawaiian lavas has remained homogeneous over similar to1.5 Myr. The Sr-87/Sr-86-Pb-206/Pb-204 variation in the stratigraphically lowest lavas is orthogonal to the all-Hawaii variation, indicating that it is not the result of mixing between components normally sampled by Hawaiian shield-stage magmas. We compare our West Maui data with observed compositions of Pacific oceanic basaltic and gabbroic crust, and predicted compositions for 2 Ga basaltic and gabbroic oceanic crust. The observed fine-scale compositional variability in the stratigraphically lowest West Main lavas is consistent with 10-15% mixing of small-degree (2%) partial melts of the Pacific gabbroic oceanic crust with plume-derived, Kea-type magmas. Mass balance considerations indicate that this geochemical signal can be present in no more than 5% of the total volume of lavas erupted at West Maul.