Noble gas study of Yamato-82192 lunar meteorite

• Main Author: Nobuo Takaoka
• Format: Report
• Language: English
• Published: Department of Earth Sciences, Faculty of Science, Yamagata University 1987
• Subjects: Yamato; Allan Hills; Antarc*; Antarctica; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2123; http://id.nii.ac.jp/1291/00002123/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2123&item_no=1&attribute_id=18&file_no=1

Concentrations and isotopic ratios of noble gases in matrix and glassy clast of the lunar meteorite Yamato-82192 are reported. Trapped gases are greatly depleted compared with other lunar meteorites (Yamato-791197 and Allan Hills A81005). However, the meteorite retains radiogenic ^<40>Ar quantitatively. The K-Ar age is 3.9±0.5 Ga, in good agreement with the ^<39>Ar-^<40>Ar age of Y-791197 and lunar highland rocks. From the three-isotope plot of Ne and the abundance pattern of the trapped gas, the trapped gas is of solar-type. The cosmogenic ^<22>Ne/^<21>Ne and ^<131>Xe/^<126>Xe ratios suggest low shielding. A model to explain the noble gas data is that the meteorite is composed of a mixture of regoliths from different shielding depths. The regolith mixture was compacted to breccia by a meteorite impact and resided at the low shielding depth of less than 40g/(cm)^2 for 20 to 40 m. y. The present specimen was produced from the interior of this regolith breccia by another meteorite impact and was thrown out to space. After the flight in space probably for less than 2 m. y., it fell in Antarctica.