Rumuruti chondrites: Noble gases, exposure ages, pairing, and parent body history

摘要

In this paper, we present concentration and isotopic composition of the light noble gases He, Ne, and Ar as well as of Kr-84, Xe-132, and Xe-129 in bulk samples of 33 Rumuruti (R) chondrites. Together with previously published data of six R chondrites, exposure ages are calculated and compared with those of ordinary chondrites. A number of pairings, especially between those from Northwest Africa (NWA), are suggested, so that only 23 individual falls are represented by the 39 R chondrites discussed here. Eleven of these meteorites, or almost 50%, contain solar gases and are thus regolithic breccias. This percentage is higher than that of ordinary chondrites, howardites, or aubrites. This may imply that the parent body of R chondrites has a relatively thick regolith. Concentrations of heavy noble gases, especially of Kr, are affected by the terrestrial atmospheric component, which resides in weathering products. Compared to ordinary chondrites, Xe-129/Xe-132 ratios of R chondrites are high.