​NICKLAS, R.W., HAHN, R.K.M., WILLHITE, L.N., JACKSON, M.G., ZANON, V., AREVALO, R., DAY, J.M.D. (2022) - Oxidized mantle sources of HIMU- and EM-type Ocean Island Basalts. Chemical Geology 602, doi: 10.1016/j.chemgeo.2022.120901. 

​Oxygen fugacity (fO₂) is a fundamental variable in igneous petrology with utility as a potential tracer of recycled high Fe⁺³/ΣFe surficial materials in the sources of mantle-derived lavas. It has been postulated that ocean island basalts (OIB) have elevated fO₂ relative to mid-ocean ridge basalts (MORB) owing to higher average Fe⁺³/ΣFe in their source regions. To examine this issue, trace-element systematics of olivine grains are reported from OIB lavas with HIMU (high-μ; Mangaia, Canary Islands), enriched mantle (EM; Samoa; São Miguel in the Azores Islands) and depleted MORB mantle (DMM; Pico in the Azores Islands) Sr-Nd-Pb-Os isotope signatures, in order to constrain the fO₂ of each magmatic system. Despite sampling distinct mantle reservoirs based on radiogenic isotope systematics, these OIB suites show similar fO₂, ranging from +0.8 to +2.6 ΔFMQ, with an average of +1.5 ± 0.8 ΔFMQ, largely higher than MORB using the same oxybarometry method at +0.6 ± 0.2 ΔFMQ. The studied OIB show no correlation between fO₂ and bulk rock isotopic ratios or calculated parental magma compositions. The lack of correlations with isotopic signatures likely results from radiogenic isotope signatures being hosted in volumetrically minor trace element enriched mantle lithologies, while Fe⁺³/ΣFe ratios that act as the primary control on fO2 are controlled by the volumetrically dominant mantle component. Higher fO₂ in many OIB relative to MORB implies that they sample a uniformly high Fe⁺³/ΣFe plume source mantle that may be the result of either a common oxidized oceanic crust-rich reservoir parental to many modern plume lavas, or preservation of un-degassed and oxidized mantle domains formed shortly after core formation.