Department of Earth Sciences, Faculty of Science, Yamagata University/Department of Earth Sciences, Faculty of Science, Yamagata University
Abstract
Unique meteorite Yamato-74063 contains large amounts of trapped heavy noble gases whereas it is depleted in trapped He and Ne. The concentration of trapped ^Ar is comparable with that of E- and C-chondrites and ureilites. Trapped ^Xe is unusually abundant. Y-74063 contains a very high concentration of radiogenic ^Xe. Trapped ^Ne/^Ar is low and similar to that of ureilites. Trapped ^Ar/^Xe of 32±4 is lower than that of any meteorites ever reported. The trapped gases in Y-74063 are depleted in Ar relative to Xe. Planetary-type noble gases may be mixtures of an Ar-depleted component and the "sub-solar" or "Ar-rich" component isolated in E-chondrites. The cosmic-ray exposure age is 6.2±0.4 Ma. Gas-retention ages are calculated to be less than 3.7±0.2,and 4.8±0.4 Ga from radiogenic ^4He and ^Ar respectively. The K-Ar age older than the age of the solar system may attributed to chemical inhomogeneities resulting in an exceptionally high K concentration of the investigated sample. The gasretention ages, the large amounts of radiogenic ^Xe and the trapped noble gases indicate that the meteorite was a closed system for the noble gases since crystallization
