Noble gases in Yamato-793274 and -86032 lunar meteorites

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Isotopic abundances of noble gases are reported for whole rock samples, mineral and grain size separates prepared from lunar meteorites Yamato-793274 and -86032. Y-793274 is rich in trapped solar gases, whereas Y-86032 is depleted in them, resembling the Y-82192 and -82193 lunar meteorites. From measurements of radiogenic Ar, the K-Ar age of Y-86032 is calculated to be 3940±240 Ma, in agreement with the K-Ar and Ar-Ar ages for Y-82192 and -82193. From measurements of cosmogenic noble gases, the total duration of cosmic-ray exposure is calculated to be 510±140 and 11±1 Ma for Y-793274 and -86032,respectively. The exposure age of Y-86032 is in good agreement with that for Y-82192/3. The agreement in the K-Ar and exposure ages as well as in the trapped gas abundances supports the earlier result that Y-86032 is paired with Y-82192 and -82193. Y-793274 experienced most of exposures to cosmic-rays in the lunar regolith because the transit time from the moon to the earth has been reported to be very short, whereas it is supposed that Y-86032 experienced a large part of cosmic-ray exposure in the interplanetary space during the flight from the moon to the earth.
国立極地研究所の論文