Ancient helium and tungsten isotopic signatures preserved in mantle domains least modified by crustal recycling

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