Krypton and xenon fractionation in North American tektites

Abstract

Elemental and isotopic compositions of the noble gases have been determined in six North American tektites (4 bediasites and 2 georgiaites) and one Ivory Coast tektite. Radiogenically produced 4He may explain the large 4He/36Ar ratios measured relative to air, despite significant diffusive losses. The Ne isotopic composition is enriched in 20Ne consistent with a single stage mass fractionation process. The enormous 20Ne/36Ar enrichments observed in all tektite samples, similar to those reported from other tektites and impact glasses, are attributed to atmospheric diffusion into the samples following solidification. The North American tektites show a systematic increase in 84Kr/36Ar and 132Xe/36Ar relative to air, with enrichments greater than those determined for any other tektite group or terrestrial samples other than shales. These enrichments are inconsistent with existing models of dissolving Kr and Xe in tektite glass without elemental fractionation at atmospheric pressures equivalent to ∼40 km altitude The Kr and Xe isotopic compositions are indistinguishable from atmospheric within experimental uncertainty.