Edwin Gnos, and 12 other geoscientists report that the lunar meteorite Sayh al Uhaymir 169 consists of an impact melt breccia extremely enriched with potassium, rare-earth elements, and phosphorus [thorium, 32.7 parts per million (ppm); uranium, 8.6 ppm; potassium oxide, 0.54 weight percent], and adherent regolith. The isotope systematics of the meteorite record four lunar impact events at 3909 +/- 13 million years ago (Ma), +/-2800 Ma, +/-200 Ma, and +/-0.34 Ma, and collision with Earth sometime after 9.7 +/- 1.3 thousand years ago. With these data, we can link the impact-melt breccia to Imbrium and pinpoint the source region of the meteorite to theLalande impact crater.
The elevated Th content of the lunar Procellarum terrane was recognized during the Apollo gamma-ray remote mapping program The terrane, which includes Mare Imbrium and Mare Procellarum, is characterized by K-REE-P (or KREEP) [potassium (K), rare earth elements (REE), and phosphorus (P)] rock, which is enriched in incompatible elements. Such material was returned by all Apollo missions. KREEP-rich material is confined to areas surrounding the Imbrium basin and the Montes Carpatus– Lalande belt, where the impact deposits provide a datable marker of lunar stratigraphy. The age of the Imbrium basin has been inferred from isotope-system shock-resetting data and is debated to be either 3770 or 3850 million years old. Sayh al Uhaymir (SaU) 169 is a 206.45-g rock found in the Sultanate of Oman.
The rock consists of two lithologies. About 87% by volume (estimates based on tomographic sections) consists of a holocrystalline, fine-grained polymict impact-melt breccia (stage I ) containing 25 to 40 vol % of shocked rock and mineral clasts. The rock clasts are coarse-grained norites, gabbronorites, and mafic granulites. Crystal clasts comprise plagioclase (An57-94), orthopyroxene (En44-78 Wo1-7), olivine (Fo58-67), and minor ilmenite, clinopyroxene, spinel, tridymite, or kamacite.
The mineral chemistry of clasts suggests the presence of norites to olivine norites and subordinate, more evolved magmatites (granodiorites to granites) and a few
granulites at the impact area. No highland anorthosites (An97) were identified.
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