History of lunar meteorites Queen Alexandra Range 93069, Asuka-881757, and Yamato-793169 based on noble gas isotopic abundances, radionuclide concentrations, and chemical composition

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We investigated the characteristics and history of lunar meteorites QUE93069, Yamato-793169 and Asuka-881757 based on the abundances of all stable noble gas isotopes, the concentrations of the radionuclides 10Be, 26Al, 36Cl, and 81Kr, and the abundances of Mg, Al, K, Ca, Fe, Cl, Sr, Y, Zr, Ba, and La. Based on the solar wind and cosmic-ray irradiations QUE93069 is the most mature lunar meteorite studied up to now. The 40Ar/36Ar ratio of the trapped component is 1.87r0.16. This ratio corresponds to a time when the material was exposed to solar and lunar atmospheric volatiles around 400 Ma ago. On the other hand, Yamato-793169 and Asuka-881757 contain very little or no solar noble gases indicating that these materials resided in the top layer of the lunar regolith only briefly or not at all. For all lunar meteorites we observe a positive correlation of the concentrations of cosmic-ray produced with trapped solar noble gases. The duration of lunar regolith residence for the lunar meteorites was calculated based on cosmic-ray produced 21Ne, 38Ar, 78Kr, 83Kr, and 126Xe and appropriate production rates that were derived based on the target element abundances and the shielding indicator 131Xe/126Xe. For QUE93069, Yamato-793169, and Asuka-881757 we obtained 1000r400 Ma, 50r10 Ma, and < 1 Ma, respectively. Both Asuka-881757 and Yamato-793169 show losses of radiogenic 4He from U and Th decay and Yamato- 793169 also 40Ar loss from K-decay. For Asuka-881757 we calculate a K-Ar gas retention age of 3100r600 Ma and a 244Pu-136Xe fission age of 4240r170 Ma. This age is one of the oldest formation ages ever observed for a lunar basalt. The exposure history of QUE93069 after ejection from the Moon was derived from the radionuclide concentrations: ejection 0.16r0.03 Ma ago, duration of Moon-Earth transit 0.15r0.02 Ma and fall on Earth < 0.015 Ma ago. This ejection event is distinguished temporally from those which produced the other lunar meteorites. We conclude that six to eight events are necessary to eject all the known lunar meteorites.

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