Cosmic-ray exposure and gas retention ages of the Guangmingshan (H5) chondrite
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Isotopic compositions of noble gases from the Guangmingshan chondrite were analyzed. Based on the analyses of cosmogenic nuclei, cosmic-ray exposure age of the meteorite is (65±10.0) Ma (3He), (80±12) Ma (21Ne) and (65±10.0) Ma (38Ar), with an average of 70 Ma. This is the highest exposure age of H-group ordinary chondrites. Gas retention ages of K-Ar and U, Th-4He are (4230±100) Ma and (3300±60) Ma, respectively. The smaller ages of3He than21Ne and4He than40Ar suggest that both3He and4He lost together. This is probably related to a solar heating effect of a meteorite with a small perihelion during the last exposure period.
Keywordsnoble gas cosmic-ray exposure age meteorite chondrite Zhuanghe Liaoning
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