The concentration and isotopic composition of hydrogen, carbon and nitrogen in carbonaceous meteorites

Abstract

Concentrations and isotopic compositions were determined for H_2, N_2 and C extracted by stepwise pyrolysis from powdered meteorites, from residues of meteorites partially dissolved with aqueous HF, and from residues of meteorites reacted with HF-HCl solutions. The meteorites treated were the carbonaceous chondrites, Orgueil, Murray, Murchison, Renazzo and Cold Bokkeveld. Data determined for whole rock samples are in approximate agreement with previously published data. Acidification of the meteorites removed the inorganic sources of H_2, so that H_2 in the HF-HCl acid residues came primarily from insoluble organic matter, which makes up 70–80% fraction of the total carbon in carbonaceous meteorites. The δD in the organic matter differs markedly from previously determined values in organic matter in meteorites. The δD values of organic matter from acid residues of C1 and C2 carbonaceous chondrites range from +650 to + 1150%. The acid residues of the Renazzo meteorite, whose total H_2 has a δD of +930‰, gave a δD value of +2500‰. Oxidation of the HF-HCl residue with H_2O_2 solution removes the high δD and the low δ^(15)N components. The δ^(13)C values range between −10 and −21 and δ^(15)N values range between +40 and −11. The δ^(15)N of Renazzo is unusual; its values range between +150 and −190. There is good correlation between δD and the concentration of H_2 in the acid residues, but no correlation exists between δD, δ^(13)C and δ^(15)N in them. A simple model is proposed to explain the high δD values, and the relationships between δD values and the concentration of H_2. This model depends on the irradiation of gaseous molecules facilitating reaction between ionic molecules, and indicates that an increase in the rate of polymerization and accumulation of organic matter on grains would produce an increase in the deuterium concentration in organic matter.

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