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Highly siderophile element abundances and 182W/184W and 187Os/188Os were determined for a suite of Mauna Kea lavas from the Hawaiian Scientific Drilling Project phase 2 drill core. The new analyses, combined with previous measurements, compose the largest database for μ182W (the parts-per-million deviation of 182W/184W from a terrestrial standard) for a single volcano (n = 16). Although most lavas analyzed are characterized by negative μ182W values, lavas with values similar to the modern bulk silicate Earth are found throughout the entire stratigraphic column. This suggests that components with normal μ182W are collocated with components that host μ182W deficits in the plume. Negative μ182W values are associated with elevated 3He/4He, as well as elevated Ti and Nb. These correlations may link μ182W anomalies to ancient deep mantle crystal-liquid fractionation processes. Consistent with previously measured 3He/4He (R/RA) in the drill core, the magnitude of negative μ182W values was greatest when Mauna Kea was close to the plume axis then generally decreased over the ~400 kyr captured by the stratigraphic section. The component with anomalous μ182W was either concentrated near the plume axis, or was more effectively sampled by melting near the plume axis where the temperature excess was greatest, suggesting it was less fusible than the dominant plume components. The process leading to the generation of a mantle component with a negative μ182W anomaly could either be related to some form of core-mantle isotopic equilibration, or early-Earth fractionation within the silicate Earth. At present each possibility remains viable. 

Mantle plumes contain heterogenous chemical components and sample variable depths of the mantle, enabling glimpses into the compositional structure of Earth's interior. In this study, we evaluated ocean island basalts (OIB) from nine plume locations to provide a global and systematic assessment of the relationship betweenfO₂and He‐Sr‐Nd‐Pb‐W‐Os isotopic compositions. Ocean island basalts from the Pacific (Austral Islands, Hawaii, Mangaia, Samoa, Pitcairn), Atlantic (Azores, Canary Islands, St. Helena), and Indian Oceans (La Réunion) reveal thatfO₂in OIB is heterogeneous both within and among hotspots. Taken together with previous studies, global OIB have elevated and heterogenousfO₂(average = +0.5 ∆FMQ; 2SD = 1.5) relative to prior estimates of global mid‐ocean ridge basalts (MORB; average = −0.1 ∆FMQ; 2SD = 0.6), though many individual OIB overlap MORB. Specific mantle components, such as HIMU and enriched mantle 2 (EM2), defined by radiogenic Pb and Sr isotopic compositions compared to other OIB, respectively, have distinctly highfO₂based on statistical analysis. ElevatedfO₂in OIB samples of these components is associated with higher whole‐rock CaO/Al₂O₃and olivine CaO content, which may be linked to recycled carbonated oceanic crust. EM1‐type and geochemically depleted OIB are generally not as oxidized, possibly due to limited oxidizing potential of the recycled material in the enriched mantle 1 (EM1) component (e.g., sediment) or lack of recycled materials in geochemically depleted OIB. Despite systematic offset of thefO₂among EM1‐, EM2‐, and HIMU‐type OIB, geochemical indices of lithospheric recycling, such as Sr‐Nd‐Pb‐Os isotopic systems, generally do not correlate withfO₂.

 

Rare high-³He/⁴He signatures in ocean island basalts (OIB) erupted at volcanic hotspots derive from deep-seated domains preserved in Earth’s interior. Only high-³He/⁴He OIB exhibit anomalous¹⁸²W—an isotopic signature inherited during the earliest history of Earth—supporting an ancient origin of high³He/⁴He. However, it is not understood why some OIB host anomalous¹⁸²W while others do not. We provide geochemical data for the highest-³He/⁴He lavas from Iceland (up to 42.9 times atmospheric) with anomalous¹⁸²W and examine how Sr-Nd-Hf-Pb isotopic variations—useful for tracing subducted, recycled crust—relate to high³He/⁴He and anomalous¹⁸²W. These data, together with data on global OIB, show that the highest-³He/⁴He and the largest-magnitude¹⁸²W anomalies are found only in geochemically depleted mantle domains—with high¹⁴³Nd/¹⁴⁴Nd and low²⁰⁶Pb/²⁰⁴Pb—lacking strong signatures of recycled materials. In contrast, OIB with the strongest signatures associated with recycled materials have low³He/⁴He and lack anomalous¹⁸²W. These observations provide important clues regarding the survival of the ancient He and W signatures in Earth’s mantle. We show that high-³He/⁴He mantle domains with anomalous¹⁸²W have low W and⁴He concentrations compared to recycled materials and are therefore highly susceptible to being overprinted with low³He/⁴He and normal (not anomalous)¹⁸²W characteristic of subducted crust. Thus, high³He/⁴He and anomalous¹⁸²W are preserved exclusively in mantle domains least modified by recycled crust. This model places the long-term preservation of ancient high³He/⁴He and anomalous¹⁸²W in the geodynamic context of crustal subduction and recycling and informs on survival of other early-formed heterogeneities in Earth’s interior.

 

The Icelandic hotspot has erupted basaltic magma with the highest mantle‐derived³He/⁴He over a period spanning much of the Cenozoic, from the early‐Cenozoic Baffin Island‐West Greenland flood basalt province (49.8R_A), to mid‐Miocene lavas in northwest Iceland (40.2 to 47.5R_A), to Pleistocene lavas in Iceland's neovolcanic zone (34.3R_A). The Baffin Island lavas transited through and potentially assimilated variable amounts of Precambrian continental basement. We use geochemical indicators sensitive to continental crust assimilation (Nb/Th, Ce/Pb, MgO) to identify the least crustally contaminated lavas. Four lavas, identified as “least crustally contaminated,” have high MgO (>15 wt.%), and Nb/Th and Ce/Pb that fall within the mantle range (Nb/Th = 15.6 ± 2.6, Ce/Pb = 24.3 ± 4.3). These lavas have⁸⁷Sr/⁸⁶Sr = 0.703008–0.703021,¹⁴³Nd/¹⁴⁴Nd = 0.513094–0.513128,¹⁷⁶Hf/¹⁷⁷Hf = 0.283265–0.283284,²⁰⁶Pb/²⁰⁴Pb = 17.7560–17.9375,³He/⁴He up to 39.9R_A, and mantle‐like δ¹⁸O of 5.03–5.21‰. The radiogenic isotopic compositions of the least crustally contaminated lavas are more geochemically depleted than Iceland high‐³He/⁴He lavas, a shift that cannot be explained by continental crust assimilation in the Baffin suite. Thus, we argue for the presence oftwogeochemically distinct high‐³He/⁴He components within the Iceland plume. Additionally, the least crustally contaminated primary melts from Baffin Island‐West Greenland have higher mantle potential temperatures (1510 to 1630 °C) than Siqueiros mid‐ocean ridge basalts (1300 to 1410 °C), which attests to a hot, buoyant plume origin for early Iceland plume lavas. These observations support the contention that the geochemically heterogeneous high‐³He/⁴He domain is dense, located in the deep mantle, and sampled by only the hottest plumes.