The Size and Emergence of Geochemical Heterogeneities in the Hawaiian Mantle Plume Constrained by Sr-Nd-Hf Isotopic Variation Over ∼47 Million Years

Abstract

The Hawaiian-Emperor chain is the ∼6,000 km long surface expression of the deeply sourced Hawaiian mantle plume active over the past ∼81 Myr. The Hawaiian Islands ( 81–47 Ma) show only Kea compositions. New Sr-Nd-Hf isotope, trace and major element data of 23 Northwest Hawaiian Ridge (∼47–6.5 Ma) shield-stage tholeiitic basalts analyzed in this study fill a critical gap and show both Kea and Loa compositions. A logistic regression model fit to a high-quality isotopic database of Hawaiian Island basalts is used to predict Loa-type or Kea-type affinity of new NWHR isotope analyses. Daikakuji, Mokumanamana, West Nīhoa, Nīhoa, and Middle Bank erupt Loa-type compositions, a finding corroborated by their geochemical characteristics (e.g., low Th/La, CaO/Al2O3, and high Sr/Nb, Zr/Nb, SiO2). Participation of the Loa composition gradually increases toward the Hawaiian Islands with time and there is no evidence for the presence of the Lō‘ihi component along the NWHR or before ∼1 Myr. A new Hf-Nd Hawaiian array is calculated based on an up-to-date extended Hawaiian Island basalt database (n = 403). The NWHR array is slightly steeper than the Hawaiian array, suggesting minimal participation of the high Hf isotopic source component present in Hawaiian Island volcanoes before ∼6.5 Ma. This study fills a significant geochemical data gap in the Hawaiian-Emperor seamount chain, and shows that Hawaiian plume chemistry evolves significantly with time as the plume samples different deep mantle reservoirs.