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 anomalous 182W—an isotopic signature inherited during the earliest history of Earth—supporting an ancient origin of high 3He/4He. However, it is not understood why some OIB host anomalous 182W while others do not. We provide geochemical data for the highest-3He/4He lavas from Iceland (up to 42.9 times atmospheric) with anomalous 182W and examine how Sr-Nd-Hf-Pb isotopic variations—useful for tracing subducted, recycled crust—relate to high 3He/4He and anomalous 182W. These data, together with data on global OIB, show that the highest-3He/4He and the largest-magnitude 182W anomalies are found only in geochemically depleted mantle domains—with high 143Nd/144Nd and low 206Pb/204Pb—lacking strong signatures of recycled materials. In contrast, OIB with the strongest signatures associated with recycled materials have low 3He/4He and lack anomalous 182W. 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 anomalous 182W have low W and 4He concentrations compared to recycled materials and are therefore highly susceptible to being overprinted with low 3He/4He and normal (not anomalous) 182W characteristic of subducted crust. Thus, high 3He/4He and anomalous 182W are preserved exclusively in mantle domains least modified by recycled crust. This model places the long-term preservation of ancient high 3He/4He and anomalous 182W in the geodynamic context of crustal subduction and recycling and informs on survival of other early-formed heterogeneities in Earth’s interior.

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The Icelandic hotspot has erupted basaltic magma with the highest mantle-derived 3 He/ 4 He over a period spanning much of the Cenozoic, from the early-Cenozoic Baffin Island-West Greenland flood basalt province (49.8 R A ), to mid-Miocene lavas in northwest Iceland (40.2 to 47.5 R A ), to Pleistocene lavas in Iceland's neovolcanic zone (34.3 R 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 have 87 Sr/ 86 Sr = 0.703008-0.703021, 143 Nd/ 144 Nd = 0.513094-0.513128, 176 Hf/ 177 Hf = 0.283265-0.283284, 206 Pb/ 204 Pb = 17.7560-17.9375, 3 He/ 4 He up to 39.9 R A , and mantle-like δ 18 O of 5.03-5.21‰. The radiogenic isotopic compositions of the least crustally contaminated lavas are more geochemically depleted than Iceland high-3 He/ 4 He lavas, a shift that cannot be explained by continental crust assimilation in the Baffin suite. Thus, we argue for the presence of two geochemically distinct high-3 He/ 4 He 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-3 He/ 4 He domain is dense, located in the deep mantle, and sampled by only the hottest plumes.

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