He,Ne and Ar isotopes in inclusions of some iron meteorites |
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| Authors: | LK Levsky AN Komarov |
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| Institution: | All-Union Geological Institute, Isotopic Department, Srednii 72, Leningrad, USSR;Institute for Precambrian Geology and Geochronology, USSR Academy of Sciences, Leningrad, USSR |
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| Abstract: | He3, He4, Ne21 and Ar38 contents were determined in 18 metal, troilite, sehreibersite and graphite inclusions of 9 iron meteorites, by total outgassing and stepwise heating. The ratio in metal phase ranges from 3.85 to 4.65, but in non-metallic samples, from 6.70 to 30.5. The results for cosmogenic isotopes of helium, neon and argon disagree appreciably with data on accelerator-irradiated targets. It should be noted, however, that some inclusions have lost considerable amounts of gas by diffusion.Uranium contents of 22 troilite and sehreibersite samples were determined by the fission track technique. The average uranium content of troilite is 0.4-0.7 ppb. Excess He4 of unknown origin was observed in troilite inclusions. If one assumes that the excess He4 was produced by uranium decay in situ, then the apparent U-He4 age is at least 5.9 × 109 yr. |
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