Messung der Diffusionsverluste von radiogenen und spallogenen Edelgasen in Steinmeteoriten II

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Abstract
Rare gas measurements (helium and neon) were carried out on single mineral components of 10 bronzite-chondrites, 10 hypersthene-chondrites and 1 amphoterite. Diffusion losses of 3He were detected in pyroxene on most meteorites studied. The helium content of olivine was found to be far less effected by diffusion compared to pyroxene. A loss of spallogenic helium is always connected with a loss of radiogenic helium. For most of the bronzite-chondrites the loss of radiogenic helium occured only during the time of cosmic ray exposure due to a more intensive heating caused by orbits closer to the sun. Bronzitechondrites containing high amounts of primordial gases showed equal relative losses of spallogenic and radiogenic helium each. The reason for this unexpected results is not clear, but it might be that it results from a grain-size-effect and perhaps also holds true for all other meteorites as far as diffusion loss in space due to solar heating is concerned. Many of hypersthene-chondrites suffered inside their parent bodies considerable losses of radiogenic helium before their exposure to the cosmic rays. From the radiogenic helium content in pyroxene we calculated an age of 560 · 106 years for five of these meteorites, but we are not quite sure that this is a true age. It could be proved that the highly varying ratio of 3He/21Ne in chondrites cannot be attributed to diffusion losses. Variations up to a factor of 4 were confirmed. The content of 3He in the metal phase of most meteorites investigated was found to be too low up to a factor of 2. A tritium loss in space is suggested as explanation of these deficiencies.

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