Highest terrestial ³He/⁴He credibly from the core

Abstract

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 convection1,2,3,4. 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 core5,6,7,8,9. 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.

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