| dc.description.transcription | This first Saharan Lunar meteorite is a polymict anorthositic highland breccia weighing 513 g when found. It consists mostly of light-colored clasts, mainly anorthositic lithologies high in Al and Ca, and feldspathic crystalline impact melt breccias, along with glass fragments and rare melt spherules, embedded in a fine-grained, very coherent matrix. It has a shock stage of S3 (15-20 GPa), and contains abundant impact melt veins throughout. FeNi-metal particles are found associated with the veins and matrix, with ilmenite, troilite, and Ti-, Cr-spinel occurring as accessory phases. It has a high concentration of solar wind implanted gases indicative of a long residence at shallow depth within the lunar regolith. Because of the very low abundance of mafic components and the specific bulk composition, the source rock was likely a pristine highland terrain lacking igneous rocks, impact melts, mare components, KREEP, and other mafic signatures of large impact craters. Argon dating studies of DaG 262 give a wide range of ages, from as old as 3.4 b.y. to only 1.7 by., evidence of multiple late impact events and reflecting the diversity of components mixed into the final breccia assemblage. Radionuclide studies suggest that exposure at a depth of ~30 cm in the regolith lasted 500-1000 my., followed by a relatively short Moon-Earth transit of less than 150 k.y. Finally, the meteorite was moderately weathered during its terrestrial residence of 50-60 k. DaG 262 has very close chemical and mineralogical similarities to the paired Lunar meteorites OUE93069 and QUE94269, as well as similarities in ejection times, Moon-Earth transit times, and terrestrial ages. This suggests the possibility of a common ejection event for these meteorites. Two other lunar highland meteorites, MAC88104/5 and Y-86032, also share close similarities with DaG 262. The specimen pictured above is a 0.09 g fragment showing a black shock vein filled with microscopic bubbles running vertically along the left edge. The photo below shows the complete mass of DaG 262 and its interior after sectioning. | |
