Cosmic-ray exposure and gas retention ages of the Guangmingshan (H5) chondrite

Isotopic compositions of noble gases from the Guangmingshan chondrite were analyzed. Based on the analyses of cosmogenic nuclei, cosmic-ray exposure a ge of the meteorite is (65 +/- 10.0) Ma (He-3), (80 +/- 12) Ma (Ne-21) and (65 10.0) Ma (Ar-38), with an average of 70 Ma. This is the highest exposur e age of H-group ordinary chondrites. Gas retention ages of K-Ar and U, Th- He-4 are (4230 +/- 00) Ma and (3300 +/- 60) Ma, respectively. The smaller a ges of He-3 than Ne-21 and He-4 than Ar-40 suggest that both He-3 and He-4 lost together. This is probably related to a solar heating effect of a mete orite with a small perihelion during the last exposure period.