EXPOSURE HISTORY OF GLASS AND BRECCIA PHASES OF LUNAR METEORITE EET87521

Glass-rich separates were prepared from a sample of the basaltic lunar meteorite EET87521 rich in dark glass. Noble gas isotopic abundances and Al-26 and Be-10 activities were measured to find out whether shock effects associated with lunar launch helped to assemble these phases. Similar Be-10 and Al-26 activities indicate that all materials in EET 87521 had a common exposure history in the last few million years befo re launch. However, the glass contains much higher concentrations of t rapped gases and records a much longer cosmic-ray exposure, 100 Ma-150 Ma, in the lunar regolith than does the bulk sample. The different hi stories show that the glass existed long before the ejection of EET875 21. The trapped Ar-40/(36)A ratio of 1.6 +/- 0.1 implies that the luna r exposure that produced most of the stable cosmogenic noble gases beg an 500 Ma ago. Cosmogenic and trapped noble gas components correlate s trongly in various temperature-release fractions and phases of EET8752 1, which is probably because the glass contains most of the gas. The t rapped solar ratios, Ne-20/Ne-22 = 12.68 +/- 0.20 and Ar-36/Ar-38 = 5. 24 +/- 0.05 can be understood as resulting from a mixture consisting o f similar to 60% solar wind and 40% solar energetic particles (SEP). A ll EET87521 phases show a K-40-(40)A, gas retention age of similar to 3300 Ma, which is in the range of typical lunar mare basalts.