Preliminary report on the Yamato-86032 lunar meteorite: III. Ages, noble gas isotopes, oxygen isotopes and chemical abundances

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The isotope abundances of He, Ne, Ar, Kr, and Xe, including ^<81>Kr, the oxygen isotopic composition, and the concentrations of Na, K, Sc, Ti, Cr, Fe, Co, Y, Zr, La, Sm, Eu, Hf, Ta, and W were determined for the lunar meteorite Yamato-86032. Based on the radionuclide ^<81>Kr we obtain a terrestrial age of 72000±30000 years, whereas the cosmic-ray exposure age is 10.6±0.6 Ma assuming exposure of the meteorite as a small object in space. Exposure to cosmic rays occurred at shallow shielding of about 40g/cm^2. The K-Ar gas retention ages of two separate splits are 3680±300 Ma and 3810±400 Ma, respectively. All ages agree with those for the lunar meteorites Y-82192 and Y-82193 recovered in the same area on the antarctic ice. The small amounts of trapped solar wind noble gases indicate that the Y-86032 material was exposed only briefly, some grains perhaps not at all, to the solar wind. The concentrations are similar to those of the Yamato-82 lunar meteorites. The oxygen isotopic composition is within the range of that for lunar rocks. The chemical composition of the samples from Y-86032,Y-82192,and Y-82193 is uniform for most major elements but not for all minor and trace elements, probably due to inhomogeneity of the source material. From the fact that the history of Y-86032 is the same as that of Y-82192/3 we conclude that these three rocks are pieces of the same meteorite fall.
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