ISOTOPIC EVIDENCE FOR A SOLAR ARGON COMPONENT IN THE EARTHS MANTLE

Determining the presence of solar argon, krypton and xenon in the Eart h's mantle is important for understanding the source, incorporation me chanism and transport of noble gases in the Earth, as well as the evol utionary history of the Earth's atmosphere. There are strong indicatio ns in the mid-ocean ridge basalt database that solar helium and neon a re indeed present(1-3), and modelling exercises indicate that the comp ositions of all five noble gases in the Earth's primordial inventory w ere solar-like(3-5). But solar isotopic signatures of the heavier nobl e gases argon and xenon, which differ significantly from atmospheric c ompositions, have appeared only subtly if at all in analyses of mantle -derived samples(6)-their non-radiogenic isotope ratios are generally found to be indistinguishable or only slightly different from those in the atmosphere(2,7-10). The first promising isotopic evidence for a s olar-like argon component in the Earth's mantle appeared in a recent a nalysis of basalt glasses from the Hawaiian Loihi seamount(11). Here I show that recent measurements(12) of neon and argon isotopes in a sui te of mid-ocean ridge basalt samples from the southern East Pacific Ri se greatly strengthen the case for the presence of solar argon, and by inference krypton and xenon, in the Earth's mantle.