3-D elemental and isotopic composition of presolar silicon carbides

Thirteen presolar silicon carbide grains - three of supernova (SN) origin and ten of asymptotic giant branch (AGB) star origin - were examined with time-of-flight-secondary ion mass spectrometry (TOF-SIMS). The grains had been extracted from two different meteorites - Murchison and Tieschitz - using different acid residue methods. At high lateral resolution of ∼300 nm, isotopic and elemental heterogeneities within the micrometer-sized grains were detected. The trace elemental abundances, when displayed in two-element correlation plots, of Li, Mg, K, and Ca show a clear distinction between the two different meteoritic sources. The different concentrations might be attributed to differences of the host meteorites and/or of extraction methods whereas the stellar source seems to be less decisive. In one SN grain with 26Mg-enrichment from extinct 26Al, the acid treatment, as part of the grain separation procedure, affected the Mg/Al ratio in the outer rim and therefore the inferred initial 26Al/27Al ratio. A second SN grain exhibits a lateral heterogeneity in 26Al/27Al, which either is due to residual Al-rich contamination on the grain surface or to the condensation chemistry in the SN ejecta. © The Meteoritical Society, 2007.