Petrography, shock history, chemical composition and noble gas content of the lunar meteorites Yamato-82192 and -82193
The Antarctic meteorites Yamato-82192 and -82193 are lunar polymict shock-lithified fragmental breccias with a minor regolith component. They are probably paired. The breccias are composed of a great variety of lithic and mineral fragments embedded in a fine-grained, densely compacted clastic matrix. Recrystallized feldspathic rocks and breccias, and granulitic lithologies are by far the dominant rock types. Crystalline impact melt breccias are common, however the amount of devitrified glasses is negligible. Glasses, common in ALHA81005,are missing in Y-82192 and -82193. Both samples contain some large basaltic clasts. All mineral and lithic clasts are shocked, and most plagioclases are recrystallized. We found no indication that the meteorite as a whole has been shocked to more than 20 GPa. These regolith breccias may have suffered peak shock pressures in the order of 10 GPa during the lithification event. The chemical composition of Y-82192 is very similar to that of the other lunar meteorites. Major differences are the low absolute abundances of REE and their flat chondrite normalized patterns. Other incompatible elements such as Hf and K also have comparatively low concentrations similar to the REE. The siderophile elements Ni, Co, Ir, and Au have similar abundances to other lunar highland samples. There appears to be a uniform signature of siderophile elements in the old lunar highlands away from the large basins of the front side of the Moon. The noble gas content of Y-82192 is entirely different from that of Y-791197 and ALHA81005. The light noble gasses He, Ne, and Ar are dominated by spallogenic and radiogenic components while the trapped gasses are similar to those in the Apollo 17 boulder and to those of "normal" meteorites. There is no indication that Y-82192 contains, or ever contained, any solar-wind implanted noble gases.
- Memoirs of National Institute of Polar Research. Special issue
Memoirs of National Institute of Polar Research. Special issue 46, 21-42, 1987-03