The origin and evolution of the Moon remain controversial, with one of the most important questions for lunar evolution being the timing and duration of basaltic (mare) magmatism. Here we report the result of ion microprobe U-Pb dating of phosphates in a lunar meteorite, Kalahari 009, which is classified as a very-low-Ti mare-basalt breccia. In situ analyses of five phosphate grains, associated with basaltic clasts, give an age of 4.35 +/- 0.15 billion years. These ancient phosphate ages are thought to represent the crystallization ages of parental basalt magma, making Kalahari 009 one of the oldest known mare basalts. We suggest that mare basalt volcanism on the Moon started as early as 4.35 Gyr ago, relatively soon after its formation and differentiation, and preceding the bulk of lunar volcanism which ensued after the late heavy bombardment around 3.8-3.9 Gyr (refs 7 and 8). Considering the extremely low abundances of incompatible elements such as thorium and the rare earth elements in Kalahari 009 (ref. 9) and recent remote-sensing observations illustrating that the cryptomaria tend to be of very-low-Ti basalt type, we conclude that Kalahari 009 is our first sample of a very-low-Ti cryptomare from the Moon.

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Abstract-Recent results of isotopic dating studies ( 182 26 Mg) and the increasing number of observed igneous and metamorphosed fragments in (primitive) chondrites provide strong evidence that accretion of differentiated planetesimals predates that of primitive chondrite parent bodies. The primitive chondrites Adrar 003 and Acfer 094 contain some unusual fragments that seem to have undergone recrystallization. Magnesium isotope analyses reveal no detectable radiogenic 26 Mg in any of the studied fragments. The possibility that evidence for 26 Al was destroyed by parent body metamorphism after formation is not likely because several other constituents of these chondrites do not show any metamorphic features. Since final accretion of a planetesimal must have occurred after formation of its youngest components, formation of these parent bodies must thus have been relatively late (i.e., after most 26 Al had decayed). Al-Mg isotope data for some igneous-textured clasts (granitoids and andesitic fragments) within the two chondrite regolith breccias Adzhi-Bogdo and Study Butte reveal also no evidence for radiogenic 26 Mg. As calculated from the upper limits, the formation of these igneous clasts, the incorporation into the parent body regolith, and the lithification must have occurred at least 3.8 Myr (andesite in Study Butte) and 4.7 Myr (granitoids in Adzhi-Bogdo) after calciumaluminum-rich inclusions (CAI) formation. The absence of 26 Mg excess in the igneous inclusions does not exclude 26 Al from being a heat source for planetary melting. In large, early formed planetesimals, cooling below the closure temperature of the Al-Mg system may be too late for any evidence for live 26 Al (in the form of 26 Mg excess) to be preserved. Thus, growing evidence exists that chondritic meteorites represent the products of a complex, multi-stage history of accretion, parent body modification, disruption and re-accretion.

Abstract-In 1999, the first meteorites from Botswana were recovered. Most samples (seven) were purchased from natives in the small village of Kuke. We suggest that these samples were found close to Kuke in the Kalahari desert. As reported by the finder, the other four samples were recovered during geological field work in various areas of Botswana in April (Mabe), September (Kalahari 008 and 009), and November 1999 (Matisama). Kalahari 008 and Kalahari 009 were found close to the small village of Kuke and are chemically and petrographically different lunar rocks. However, we suggest that both samples represent distinct lithologies of one meteoroid and that the lunar sample broke apart at the find site. The other nine samples are H-group ordinary chondrites. Based on different petrologic types, the degrees of shock metamorphism and weathering pairing of most samples can be ruled out. We conclude that only Kalahari 004 and Kalahari 005 are paired.