Noble gas record and cosmic-ray exposure history of the new CO3 chondrite Moss--Comparison with Lancé and other CO chondrite falls

摘要

Abstract- The Moss meteorite is the first CO chondrite fall after a time period of 70 yr and the least terrestrially contaminated member of its group. Its cosmic-ray exposure (CRE) age (T_3 ~ 13.5 Ma; T_(21) ~ 14.6 Ma) is distinct among CO chondrites and, within witnessed falls is the shortest after Lancé, which we have reanalyzed. Gas retention ages are approximately 3.95 × 10~9 yr (U/Th-He) and approximately 4.43 × 10~9 yr (K/Ar), respectively. Trapped Ar, Kr, and Xe are present in Moss in abundances typical for CO chondrites, with "planetary" elemental and isotopic compositions. Presence of HL-xenon from presolar diamonds is observed in the stepwise release analysis of Lancé. It may also be present in Moss, but it is difficult to ascertain in single-step bulk analyses. It follows from our new data combined with a survey of the literature that the abundance of trapped gases in CO chondrites is not a good indicator of their petrological subtype.