Studies on the Primordial Noble Gases and the Carrier Phases in Carbonaceous Chondrites Using the Laser Microprobe.

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Since the primordial noble gas component gives us informations about the formation of solar system, noble gas studies on primitive meteorites are very important to know the history of an initial stage of solar system. It is known that the primordial noble gases are distributed inhomogeniously in carbonaceous chondrites. We attempted to investigate the noble gas carrier phases and their position in meteorite using the laser microprobe for noble gas extraction from spot area in the meteorite. Noble gas mass spectrometer and software for noble gas analysis have been improved to be able to measure extremely small amount of noble gases accurately and quickly.More than 40 points of Allende and Murchison carbonaceous chondrites have been analyzed. Some of the interesting results obtained until now are followings ;1) Anomarously high concentrations of ^4He, ^<40>Ar and ^<129>Xe in CAIs of Allende imply high concentrations of volatile elements K and I as well as high U content in CAIs. As CAIs are thought to be high temperature condensates, the high concentrations of volatiles are difficult to be explained.2) Isotopic ratios of trapped Ne in chondrules are different between Allende and Murchison, which may suggest different circumstances for chondrule formation of these chondrites.