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Abstract—Thirteen glasses from Apollo 17 regolith 71501,262 have been chemically analyzed by electron microprobe and isotopically dated with the 40Ar/39Ar dating method. We report here the first isotopic age obtained for the Apollo 17 very low titanium (VLT) volcanic glasses, 3630 ± 40 Ma. Twelve impact glasses that span a wide compositional range have been found to record ages ranging from 102 ± 20 Ma to 3740 ± 50 Ma. The compositions of these impact glasses show that some have been produced by impact events within the Apollo 17 region, whereas others appear to be exotic to the landing site. As the data sets that include compositions and ages of lunar impact glasses increase, the impact history in the Earth‐Moon system will become better constrained.

AbstractThe major‐ and minor‐element abundances were determined by electron microprobe in 1039 glasses from regoliths and regolith breccias to define the compositional topology of lunar glasses at the Apollo 16 landing site in the central highlands of the Moon. While impact glasses with chemical compositions similar to local materials (i.e., Apollo 16 rocks and regoliths) are abundant, glasses with exotic compositions (i.e., transported from other areas of the Moon) account for up to ˜30% of the population. A higher proportion of compositionally exotic, angular glass fragments exists when compared to compositionally exotic glass spherules. Ratios of non‐volatile lithophile elements (i.e., Al, Ti, Mg) have been used to constrain the original source materials of the impact glasses. This approach is immune to the effects of open‐system losses of volatile elements (e.g., Si, Na, K). Four impact glasses from one compositionally exotic group (low‐Mg high‐K Fra Mauro; lmHKFM) were selected for 40Ar/39Ar dating. The individual fragments of lmHKFM glass all yielded ages of ˜3750 ± 50 Ma for the time of the impact event. Based on the petrography of these individual glasses, we conclude that the likely age of the impact event that formed these 4 glasses, as well as the possible time of their ballistic arrival at the Apollo 16 site from a large and distant cratering event (perhaps in the Procellarum KREEP terrain) (Zeigler et al. 2004), is 3730 ± 40 Ma, close to the accepted age for Imbrium.

Abstract—We analyzed noble gases from 18 samples of weathering products (“iddingsite”) from the Lafayette meteorite. Potassium‐argon ages of 12 samples range from near zero to 670 ± 91 Ma. These ages confirm the martian origin of the iddingsite, but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40Ar. In any case, because iddingsite formation requires liquid water, this data requires the presence of liquid water near the surface of Mars at least as recently as 1300 Ma ago, and probably as recently as 650 Ma ago. Krypton and Xe analysis of a single 34 μg sample indicates the presence of fractionated martian atmosphere within the iddingsite. This also confirms the martian origin of the iddingsite. The mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas.

Abstract—We studied the petrography, mineralogy, bulk chemical, I‐Xe, and O‐isotopic compositions of three dark inclusions (E39, E53, and E80) in the reduced CV3 chondrite Efremovka. They consist of chondrules, calcium‐aluminum‐rich inclusions (CAIs), and fine‐grained matrix. Primary minerals in chondrules and CAIs are pseudomorphed to various degrees by a mixture largely composed of abundant (>95%), fine‐grained (>0.2 μm) fayalitic olivine (Fa35–42) and minor amounts of chlorite, poorly‐crystalline Si‐Al‐rich material, and chromite; chondrule and CAI shapes and textures are well‐preserved. Secondary Ca‐rich minerals (Ti‐andradite, kirschsteinite, Fe‐diopside) are common in chondrule pseudomorphs and matrices in E39 and E80. The degree of replacement increases from E53 to E39 to E80. Fayalitic olivines are heavily strained and contain abundant voids similar to those in incompletely dehydrated phyllosilicates in metamorphosed CM and CI chondrites. Opaque nodules in chondrules consist of Ni‐ and Co‐rich taenite, Co‐rich kamacite, and wairauite; sulfides are rare; magnetite is absent. Bulk O‐isotopic compositions of E39 and E53 plot in the field of aqueously altered CM chondrites, close to the terrestrial fractionation line; the more heavily altered E39 is isotopically heavier than the less altered E53. The apparent I‐Xe age of E53 is 5.4 Ma earlier than Bjurböle and 5.7 ± 2.0 Ma earlier than E39. The I‐Xe data are consistent with the most heavily altered dark inclusion, E39 having experienced either longer or later alteration than E53. Bulk lithophile elements in E39 and E53 most closely match those of CO chondrites, except that Ca is depleted and K and As are enriched. Both inclusions are depleted in Se by factors of 3–5 compared to mean CO, CV, CR, or CK chondrites. Zinc in E39 is lower than the mean of any carbonaceous chondrite groups, but in E53 Zn is similar to the means in CO, CV, and CK chondrites.

Abstract—Eagles Nest and Lewis Cliff (LEW) 88763 are olivine‐rich achondrites that have been suggested to be related to Brachina and ALH 84025. Both are ultramafic, although LEW 88763 has ∼10% plagioclase, which Eagles Nest lacks. Olivine in Eagles Nest (Fo68) is virtually identical in composition to that in Brachina (Fo68–70), and that in LEW 88763 is only slightly different (Fo63–64). The meteorites' cosmic‐ray exposure ages differ from each other and from Brachina and ALH 84025. Like Brachina, Eagles Nest has a substantial amount of radiogenic 129Xe and an apparent K‐Ar age of <4.5 Ga. Lewis Cliff 88763, on the other hand, has no detectable radiogenic 129Xe, an apparent K‐Ar age of ∼4.5 Ga, and a substantial amount of trapped Xe. The chemical composition of LEW 88763 is within a factor of two of chondritic for virtually every element analyzed, including siderophiles, which suggests that it was melted (or at least heated and recrystallized) in a closed system. Analyses of the chemical composition of Eagles Nest are hampered by extensive terrestrial weathering; but it appears to be broadly chondritic also, although it, like Brachina, is depleted in siderophiles. Our data suggest that Eagles Nest is genetically related to Brachina but that LEW 88763 is not, which is a conclusion that is consistent with the O isotopic data of Clayton and Mayeda (1996).