[PPS03-P23] Polycyclic aromatic hydrocarbons and aliphatic hydrocarbons in Jbilet Winselwan carbonaceous chondrite : Attempt to evaluate the thermal metamorphism degree on the parent body
Keywords:Jbilet Winselwan meteorite, Soluble organic molecules, Dehydration
Samples and Methods: Powdered samples of Jbilet Winselwan meteorite and Murray meteorite (0.2 - 0.4g) were extracted with dichloromethane/methanol (9:1) by sonication. The extracts were applied to a silica gel column. From the column, aliphatic hydrocarbons were eluated with hexane and then PAHs were eluated with dichloromethane. The hexane and dichloromethane eluates were concentrated to 100 μl individually under a nitrogen flow for analysis by a gas chromatography coupled with mass spectrometry (GC-MS). Identification and quantification of compounds were made by comparison of peak retention times on mass chromatograms and mass spectra, and peak areas, respectively, with those of standard compounds. For compounds without standard compounds, identification was made by comparison of mass spectra with library data.
Results and discussion: Total concentration of n-alkanes from Jbilet Winselwan meteorite (1.85 μg/g meteorite) was 40 times lower than those from Murray meteorite (80.7 μg/g meteorite). Relative abundances of short-chain n-alkanes (C15-C16) were dominant in Jbilet Winselwan meteorite, while those of long-chain n-alkanes (C17-C21) were dominant in Murray meteorite. This difference implies that short-chain n-alkanes were resulted from cracking of long-chain n-alkanes and/or IOM during thermal metamorphism of the parent body of Jbilet Winselwan meteorite. Total concentration of PAHs from Jbilet Winselwan meteorite (0.05 μg/ meteorite) was 1000 times lower than those from Murray meteorite (62.0 μg/g meteorite). Dimethylnaphthalene, fluorine, phenanthrene, pyrene, fluoranthene, methylbiphenyl (0.003-0.039 μg/g meteorite) were identified, while low molecular weight PAHs, such as naphthalene, methylnaphthalene, and acenaphthene, were not detected. The results suggest that PAHs with high volatility in Jbilet Winselwan meteorite were lost or involved in further aromatization during thermal metamorphism. Distributions of dimethylnaphthalene and methylbiphenyl isomers in Jbilet Winselwan and Murray meteorites were similar, respectively, which indicates that the parent body of Jbilet Winselwan meteorite experienced relatively mild thermal metamorphism.