Heterogeneous enriched geochemical compositions in Hawaiian lavas: Contributions from recycled continental materials in the Loa source of the Hawaiian plume

Several mantle plumes (Hawai‘i, Kerguelen, Pitcairn) produce ocean island basalt with enriched mantle I (EM-I) geochemical compositions. Hawai‘i is the most vigorous of these plumes, with the highest buoyancy flux. The isotopically enriched, EM-I-like compositions measured along the Hawaiian Island chain are limited to the Ko‘olau, Lāna‘i, and Kaho‘olawe volcanoes, which form the Enriched Loa geochemical group. A total of 37 new samples from seven locations across the Wai‘anae and Ko‘olau volcanoes (O‘ahu, Hawai‘i) were analysed for major element oxides, trace element concentrations, and Pb-Sr-Nd-Hf isotopic compositions to determine the composition and spatial distribution of Enriched Loa compositions along the Hawaiian chain. Combined with data from Lāna‘i and Kaho‘olawe, and a compilation of shield stage Hawaiian data spanning ∼6 Ma, this study shows that Enriched Loa compositions are chemically heterogeneous and that the Enriched Loa component was present intermittently along the Hawaiian chain over approximately 130 km and 1.4 Ma. The statistically distinct Pb-Sr-Nd-Hf isotopic means between the Makapu‘u stage of Ko‘olau, Lāna‘i, and Kaho‘olawe suggest that the Enriched Loa geochemical group consists of two different heterogeneities and implies that enriched components in the deep mantle source of the Hawaiian plume exist at multiple physical scales. The geochemical features of the Enriched Loa volcanoes require a distinct mantle component, with a source that likely contains recycled surface materials, possibly of continental origin, stored in the Pacific large low shear velocity province (LLSVP). Enriched Loa isotopic compositions share similarities with other EM-I ocean island basalt; however, they are not as radiogenic in ⁸⁷Sr/⁸⁶Sr as compositions from Kerguelen and Pitcairn. This suggests that the materials stored in the Pacific and African LLSVPs have slightly different sources and ages. Specifically, this work supports the hypothesis that the recycled surface materials from the Pacific LLSVP are younger than those from the African LLSVP.