Isotopic evidence for a solar argon component in the Earth's mantle

Abstract

Determining the presence of solar argon, krypton and xenon in the Earth's mantle is important for understanding the source, incorporation mechanism and transport of noble gases in the Earth, as well as the evolutionary history of the Earth's atmosphere. There are strong indications in the mid-ocean ridge basalt database that solar helium and neon are indeed present1,2,3, and modelling exercises indicate that the compositions of all five noble gases in the Earth's primordial inventory were solar-like3,4,5. But solar isotopic signatures of the heavier noble gases argon and xenon, which differ significantly from atmospheric compositions, have appeared only subtly if at all in analyses of mantle-derived samples6 — their non-radiogenic isotope ratios are generally found to be indistinguishable or only slightly different from those in the atmosphere2,7,8,9,10. The first promising isotopic evidence for a solar-like argon component in the Earth's mantle appeared in a recent analysis of basalt glasses from the Hawaiian Loihi seamount11. Here I show that recent measurements12 of neon and argon isotopes in a suite of mid-ocean ridge basalt samples from the southern East Pacific Rise greatly strengthen the case for the presence of solar argon, and by inference krypton and xenon, in the Earth's mantle.