Highest terrestrial 3He/4He credibly from the core.

The observation that many lavas associated with mantle plumes have higher ³He/⁴He ratios than the upper convecting mantle underpins geophysical, geodynamic and geochemical models of Earth’s deep interior. High ³He/⁴He ratios are thought to derive from the solar nebula or from solar-wind-irradiated material that became incorporated into Earth during early planetary accretion. Traditionally, this high-³He/⁴He component has been considered intrinsic to the mantle, having avoided outgassing caused by giant impacts and billions of years of mantle convection1–4. Here we report the highest magmatic ³He/⁴He ratio(67.2 ± 1.8 times the atmospheric ratio) yet measured in terrestrial igneous rocks, in olivines from Baffin Island lavas. We argue that the extremely high-³He/⁴He helium in these lavas might derive from Earth’s core5–9. The viability of the core hypothesis relaxes the long-standing constraint—based on noble gases in lavas associated with mantle plumes globally—that volatile elements from the solar nebula have survived in the mantle since the early stages of accretion.Olivines from Baffin Island lavas have the highest magmatic ³He/⁴He ratio measured so far in terrestrial igneous rocks, indicating that the helium in these lavas might derive from Earth’s core. [ABSTRACT FROM AUTHOR]