Thermal processing carbonaceous chondrites

Huss GR, Meshik AP, Smith JB, Hohenberg CM (2003) Presolar diamond, silicon carbide, and graphite in carbonaceous chondrites implications for thermal processing in the solar nebula. Geochim Cosmochim Acta 67 4823-4848... 

Meteorites provide perhaps the best record of the chemical evolution of small bodies in the Solar System, and this record is supplemented by asteroidal spectroscopy. Meteorites show progressive degrees of thermal processing on their parent asteroids, from primitive carbonaceous chondrites that contain percent-level quantities of water, through ordinary chondrites that show a wide range of degree of thermal metamorphism, to the achondrites that have been melted and differentiated. 

Alteration and metamorphism used to be considered as separate processes the former affecting carbonaceous bodies and the latter operating on enstatite and ordinary chondrites. However, it is now clear that fluids of some kind were present during thermal processing of virtually all chondrite classes. 

The most primitive of the chondritic meteorites are thought to represent the "raw material" from which the Earth and other terrestrial planets were accreted. These most primitive chondrites, the Cl - carbonaceous chondrites (see Section 2.3.3.1), are identified by their high volatile content (they may contain up to 30 wt% of HaO, S, and C). They lack evidence of thermal processing after their accretion and so can be treated as the least altered condensates of the solar nebula. This view is supported by a plot of element concentrations in Cl chondrites against concentrations in the solar photosphere. There is a strong 1 1 correlation for all elements except the gaseous elements (H, He, N, O, and the... 

Figure I. The classification of carbonaceous chondrites based on their primary elemental (chemical) composition and levels of secondary (aqueous and thermal) processing. (Adaptedfrom References 4 and 5.)...

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