Predominantly carbonaceous. HF/HCl-resistant residues from the Allende meteorite were studied before and after applying physical and chemical separation methods. Samples were characterized by SEM/EDXA. X-ray diffraction. INAA. C (including isotopic composition). S. H. N and noble gas analyses. Isotopic data for carbon showed little variation (≲ 5‰); isotopic data for noble gases confirmed previously established systematics (Frick, 1977; Alaerts et al., 1980). In our samples, noble gas abundances correlated with those of C and N but not with those of S and metals; concomitant partial loss of C and 'normal' trapped gas occurred during treatments with oxidizing acids; and total gas loss accompanied combustion of carbon. In addition, HF/HCl demineralization of bulk meteorite resulted in similar fractional losses of C and trapped noble gases. These results lead us to conclude that various macromolecular carbonaceous substances serve as • -the main host phase ('Q') for 'normal' trapped noble gases in acid-resistant residues from Allende. • -the main host phase for 'anomalous' gas in the acid-resistant residues, and • -the carrier of the major part of trapped noble gases lost during HF/HCl demineralization ('solubles'). At present little information exists concerning what fraction of the carbonaceous material in Allende consists of noble gas host phases; and the possibility is not yet ruled out that very minor amounts of dense non-carbonaceous minerals also could act as trapped gas carriers, especially if they were inseparable from the lighter carbonaceous matter by our methods. Limits on the possible abundances of dense mineralic host phases in the residues have been obtained, however; if Q were an Fe/Cr mineral or a sulfide. its abundance has to be more than an order of magnitude lower than inferred previously from etching experiments (Anders et al., 1975; gros and Anders, 1977). By analogy with C1 and C2 meteorites, where carbonaceous phases play host to noble gases with anomalies of nucleogenetic origin (Alaerts et al., 1980). we also favor a nucleogenetic origin for CCF-XE. These considerations hold open the possibility that carbonaceous host phases and various forms of organic matter in carbonaceous meteorites may have had a presolar origin.
ASJC Scopus subject areas
- Geochemistry and Petrology