Trapped helium-neon isotopic correlations in gas-rich meteorites and carbonaceous chondrites

Abstract

Step wise heating experiments have been carried out on the dark portions of the gasrich meteorites Kapoeta, Fayetteville, Pantar, Nogoya, Pultusk, Holman Island and the C2 carbonaceous chondrite Nogoya light, to determine more precisely the march of trapped helium neon and argon. Isotopic variations of up to a factor of 7 exist in trapped-helium and correlate with variations in trapped neon. A plot of trapped 3He 4He and 20Ne 22Ne ratios shows that gas-rich meteorites define a zone, called the GRZ. The carbonaceous chondrite Nogoya and several analyses of the carbonaceous chondrite Mokoia define a “carbonaceous chondrite corridor” which is distinct from the GRZ. Trapped helium and neon in meteorites is found to result from a multicomponent mixture. The primary trapped components may be related by a nuclear process; mass fractionation is shown to have played a minor role in altering the trapped helium-neon compositions.