HISTORY OF LUNAR METEORITES QUEEN-ALEXANDRA RANGE-93069, ASUKA-881757, AND YAMATO-793169 BASED ON NOBLE-GAS ISOTOPIC ABUNDANCES, RADIONUCLIDE CONCENTRATIONS, AND CHEMICAL-COMPOSITION

We investigated the characteristics and history of lunar meteorites Qu een Alexandra Range 93069, Yamato 793169 and Asuka 881757 based on the abundances of all stable noble gas isotopes, the concentrations of th e radionuclides Be-10, Al-26, Cl-36 and Kr-81, and the abundances of M g, Al, K, Ca, Fe, Cl Sr, Y, Zr, Ba, and La. Based on the solar wind an d cosmic-ray irradiations, QUE 93069 is the most mature lunar meteorit e studied up to now. The Ar-40/Ar-36 ratio of the trapped component is 1.87 +/- 0.16. This ratio corresponds to a time when the material was exposed to solar and lunar atmospheric volatiles similar to 400 Ma ag o. On the other hand, Yamato 793169 and Asuka 881757 contain very litt le or no solar noble gases, which indicates that these materials resid ed 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 con centrations of cosmic-ray produced with trapped solar noble gases. The duration of lunar regolith residence for the lunar meteorites was cal culated based on cosmic-ray produced Ne-21, Ar-38, Kr-78, Kr-83, and X e-126 and appropriate production rates that were derived based on the target element abundances and the shielding indicator Xe-131/Xe-126. F or QUE 93069, Yamato 793169, and Asuka 881757, we obtained 1000 +/- 40 0 Ma, 50 +/- 10 Ma, and < 1 Ma, respectively. Both Asuka 881757 and Ya mato 793169 show losses of radiogenic He-4 from U and Th decay and Yam ato 793169 also Ar-40 loss from K-decay. For Asuka 881757, we calculat e a K-Ar gas retention age of 3100 +/- 600 Ma and a Pu-244-Xe-136 fiss ion age of 4240 +/- 170 Ma. This age is one of the oldest formation ag es ever observed for a lunar basalt. The exposure history of QUE 93069 after ejection from the Moon was derived from the radionuclide concen trations: ejection 0.16 +/- 0.03 Ma ago, duration of Moon-Earth transi t 0.15 +/- 0.02 Ma and fall on Earth < 0.015 Ma ago. This ejection eve nt is distinguished temporally from those which produced the other lun ar meteorites. We conclude that six to eight events are necessary to e ject all the known lunar meteorites.