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Helium isotopes are used as a tracer for primitive reservoirs that have persisted in the Earth’s mantle. Basalts erupted at several intraplate oceanic islands, including Hawaii, Iceland, Galapagos, and Samoa, have hosted the highest ³He/⁴He ratios (>30 Ra, where Ra is atmospheric ³He/⁴He ratio) globally that are far in excess of the ³He/⁴He typical of the upper mantle sampled at mid-ocean ridges (8 Ra). These lavas have been suggested to be melts of a primitive, or possibly slightly depleted, mantle reservoir, i.e., either fertile or a depleted peridotite. Here we report evidence for geochemical enrichment in the high-³He/⁴He mantle sampled by lavas with the highest ³He/⁴He from Hawaii, Samoa, and possibly Galapagos. The titanium concentrations in high-³He/⁴He lavas from Samoa are too high to be explained by melts of a mantle peridotite, even at infinitesimally small degrees of melting, and the elevated Ti …