Molecular and compound-specific hydrogen isotope analyses of insoluble organic matter from different carbonaceous chondrite groups

We have conducted the first systematic analyses of molecular distribution and delta D values of individual compounds in pyrolysates of insoluble organic matter (TOM) from different carbonaceous chondrite groups, using flash pyrolysis coupled to gas chromatography-mass spectrometry and compound-specific D/H analysis. TOM samples from six meteorites of different classifications, Elephant Moraine (EET) 92042 (CR2), Orgueil (CII), Allan Hills (ALH) 83100 (CM1/2), Murchison (CM2), ALH 85013 (CM2), and Tagish Lake (C2) were isolated and studied. Except for the pyrolysate of Tagish Lake TOM, pyrolysates of all five meteorite TOM samples were dominated by an extensive series of aromatic (C, to C, alkyl-substituted benzenes, C(0) to C2 alkyl-substituted naphthalenes), with aliphatic (straight chain and branched C(1) to C(2) alkanes) hydrocarbons and several S- and O- containing compounds (C(1) to C(2) alkylthiophenes, benzothiophene, benzaldehyde) being also present. The strong similarity in the pyrolysates of different carbonaceous chondrites suggests certain common characteristics in the formation mechanisms of TOM from different meteorites. The Tagish Lake TOM sample is unique in that its pyrolysate lacks most of the alkyl-substituted aromatic hydrocarbons detected in other meteorite TOM samples, suggesting distinctively different formation processes. Both bulk delta D values of meteorite IOMs and weighted-average delta D values of individual compounds in pyrolysates show a decreasing trend: CR2 > CH > CM2 > C2 (Tagish Lake), with the EET 92042 (CR2) TOM having the highest delta D values (similar to 2000%o higher than other samples). We attribute the high D contents in the TOM to primitive interstellar organic sources. Copyright (c) 2005 Elsevier Ltd.