Noble gas record, collisional history, and pairing of CV, CO, CK, and other carbonaceous chondrites

Concentration and isotopic composition of the light noble gases as well as of Kr-84, Xe-129, and Xe-132 have been measured in bulk samples of 60 carbonaceous chondrites; 45 were measured for the first time. Solar noble gases were found in nine specimens (Arch, Acfer 094, Dar al Gani 056, Graves Nunataks 95229, Grosnaja, Isna, Mt. Prestrud 95404, Yamato (Y) 86009, and Y 86751). These meteorites are thus regolith breccias. The CV and CO chondrites contain abundant planetary-type noble gases, but not CK chondrites. Characteristic features of CK chondrites are high Xe-129/Xe-132 ratios. The petrologic type of carbonaceous chondrites is correlated with the concentration of trapped heavy noble gases, similar to observations shown for ordinary chondrites. However, this correlation is disturbed for several meteorites due to a contribution of atmospheric noble gases, an effect correlated to terrestrial weathering effects. Cosmic-ray exposure ages are calculated from cosmogenic Ne-21. They range from about 1 to 63.5 Ma for CO, CV, and CK classes, which is longer than exposure ages reported for CM and CI chondrites. Only the CO3 chondrite Isna has an exceptionally low exposure age of 0.15 Ma. No dominant clusters are observed in the cosmic-ray exposure age distribution; only for CV and CK chondrites do potential peaks seem to develop at similar to 9 and similar to 29 Ma. Several pairings among the chondrites from hot deserts are suggested, but 52 of the 60 investigated meteorites are individual falls.