Geochemical Study on the Oldest Halite Fossil in the Solar System

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Halogens and their crystals (halide) have been investigated in Zag and other halogen containing meteorites by detecting halogen-derived noble gas isotopes ^<80>Kr, ^<82>Kr and ^<128>Xe^<129>Xe from extinct nuclide was ^<129>I also measured in these meteorites. Halide crystals are dark phase portion of the Zag meteorite. Size of most crystals are estimated to be smaller than 0.1 mm, which would be surrounded by silicates insoluble in water. Halogens are also concentrated in small materials in Yamato-74191 (L3.6) meteorite. The halogen enrichments in these meteorite are likely resulted by liquid water with high concentrations of halogens presented on their parent planetesimals. Though origin of the waters is not clear, they might have been brought through bombardment by water containing objects such as carbonaceous chondrites or comets.To study the event concerning the halogen enrichments, we constructed noble gas extraction and purification line for noble gas analysis of neutron irradiated meteorites. Modification of VG3600 noble gas mass spectrometer used for ^<40>Ar-^<39>Ar dating was carried out to improve sensitivity and stability of the mass spectrometer in the Radioisotope Center, University of Tokyo. Combining the noble gas line and the mss spectrometer, I-Xe dating of meteorites can be measurable for the first time in Japan. This method began to clarify the timing of halogen enrichment process in meteorites.