Meteorites, individual Allende

The application of the laser probe to meteorite chronology is illustrated by a study of Ca-Al-rich inclusions from the Allende meteorite [7]. This study was able to show that the K in the inclusions studied mainly concentrated in veins and rims with very little, if any, K in the major minerals. The limit obtained is something of the order of 10 ppm. On the other hand, the major minerals do contain appreciable 40Ar. Individual chondrules and the matrix were also studied in the Allende meteorite from places adjacent to the Ca-Al-rich inclusions. For these samples the ages varied from 3.3 to 4.4 G.y. There appears to be evidence that the Allende meteorite has been subjected to numerous metamorphic events, presumably of a collisional origin. 

Lee T, Papanastassiou DA, Wasserburg GJ (1977) Mg and Ca isotopic study of individual microscopic crystals from the Allende meteorite by the direct loading technique. Geochim Cosmochim Acta 41 1473-1485 Lee T, Russell WA, Wasserburg GJ (1979) Calcium isotopic anomalies and the lack of aluminum-26 in an unusual Allende inclusion. Appl J Lett 228(L93-L98) 661-662 Marshall BD, DePaolo DJ (1982) Precise age determinations and petrogenetic studies using the K-Ca method. Geochim Cosmochim Acta 46 2537-2545... 

Murchison and Allende meteorites contained a substantial number of individual crystalline carbyne grains [21] was almost certainly incorrect. In yet another ultrathin section and acid-resistant residue of the Murchison meteorite C=C functional groups were identified but they were linked to aromatic carbons [61]. The only reliable evidence for carbyne (i.e. chaoite) in meteorites [20] suggests it formed in situ by solid-state carbon annealing that is an acceptable geological process. A tenet of cosmochemistry is that all solids initially formed by condensation from a cooling vapor phase. Whether condensation proceeded at (near) thermodynamic equilibrium, kinetically controlled, metastable equilibrium, or a combination, remains open to debate. Kinetically controlled, metastable condensation is likely for silicates [6,79] and was proposed for carbyne condensation from interstellar polycyanoacetylenes [80]. 

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