Chlorine abundances in meteorites

Abstract

We used the nuclear reaction 37Cl (n,γ) 38Ar, achieved during neutron irradiation for dating meteorites by the 39Ar-40Ar technique, to calculate the elemental Cl concentration of 132 samples of 94 different meteorites (mostly finds) representing several different classes. Determined K and Ca concentrations are also reported. Total [Cl] varies considerably, both among meteorites of the same class and among different meteorite classes. The range in [Cl] is approximately 15-177 ppm for ordinary chondrites; approximately 24-650 ppm for enstatite chondrites; approximately 4-177 ppm for eucrites; approximately 7-128 ppm for mesosiderites; approximately 35-268 ppm for acapulcoites and lodranites; and approximately 12-507 ppm for winonaites and iron silicates. As expected, most differentiated meteorites have lower [Cl] compared to chondrites and iron silicates. Analyses of 11 interior samples (~0.1 g each) of a large L6 chondrite varied over 68-129 ppm, which is a measure of the homogeneity of Cl distribution. By evaluating Ar release during stepwise sample degassing, we separated the Cl into low-temperature and high-temperature components, the former of which may consist of terrestrial contamination. Most samples show low-temperature Cl concentrations of <40 ppm, but for several samples terrestrial Cl contamination constitutes significant fractions of the total Cl. Among most differentiated meteorites, finds show considerably greater low-temperature [Cl] compared to falls.