Melting in the Hawaiian plume at 1–2 Ma as recorded at Maui Nui: The role of eclogite, peridotite, and source mixing

Abstract

The volcanoes of Maui Nui (West Moloka'i, East Moloka'i, Lana'i, West Maui, Haleakala, and Kaho'olawe) record Hawaiian magmatism at ∼1–2 Ma. Lavas from these volcanoes nearly span the compositional range erupted from all the Hawaiian volcanoes over the past 5 Myr and represent both the Kea and Ko'olau compositional end‐members of Hawaiian lavas. Many aspects of major and trace element and isotope compositions of Hawaiian shield‐stage lavas are consistent with ancient, recycled oceanic lithosphere in the plume sources of Kea‐ and Ko'olau‐type magmas (Lassiter and Hauri, 1998; Blichert‐Toft et al., 1999). Hypotheses that describe the compositional range of Hawaiian lavas as originating from ancient oceanic lithosphere in the Hawaiian plume implicitly or explicitly infer lithologic heterogeneity in the plume. We present trace element models for the origin of these end‐members that explicitly address the petrologic complexities of melting eclogite (derived from ancient oceanic lithosphere) in the plume. Trace element (La/Nb, Sm/Yb, Sm/Hf, and Sm/Nb), major element, and isotope compositions of Lana'i, which erupts dominantly Ko'olau‐type lavas, are consistent with the origin of these lavas in large‐degree (∼60–70%) melts of ancient upper oceanic crust (basalt + sediment) that mix with plume‐derived Haleakala‐type melts. Trace element (Sm/Yb, Hf/Zr, and Hf/Nb) and isotope compositions of West Maui and East Moloka'i, which erupt dominantly Kea‐type magmas, are consistent with an origin in ancient depleted oceanic lithosphere that has been refertilized with moderate‐degree melts (10–30%) of associated crustal gabbro. The physical mechanisms (melt‐melt versus melt‐solid mixing) through which the oceanic crustal components melt and mix within the plume lead to the generation of isotopically homogeneous Kea‐type lavas and isotopically heterogeneous Ko'olau‐type lavas. The volcanoes of Maui Nui record the exhaustion of the Ko'olau component and the initiation of the Kea component as dominant compositional end‐members in the Hawaiian plume.