Thermal processing in the Solar System chondrites

Much of the primitive planetary material in the Solar System, which includes primitive meteorites, IDPs, and samples returned from Stardust, have been processed repeatedly within the protoplanetary disk by energetic, high-temperature events during the course of the first few million years of its existence. The strongest evidence for such processing comes from primitive meteorites known as chondrites. Chondrites are typically referred to as defining t=0 for the Solar System at 

6 Ma (Wadhwa et al. 2007 and references therein), which is actually the age of a group of inclusions within chondrites known as calcium-aluminum-rich inclusions (CAIs). The word primitive refers to the fact that the bulk compositions of all chondrites, within a factor of two, are solar in composition for all but the most volatile elements (Weisberg et al. 2006). This fact indicates that chondrites have not been through a planetary melting or differentiation process in their parent body, indicating that they have recorded the materials that were present and the processes that operated within the disk before or during planet formation. 

Chondrites are classified into five major groups based on properties such as bulk composition, petrography, and oxygen isotopic ratios (Brearley Jones 1998). They are further subdivided into several clans within these major types 

The first-order observation is that these igneous rocks were heated to temperatures up to 2200 K for seconds to minutes and then cooled between tens to hundreds of K hr-1 at pressures that stabilized silicate liquids. The energetic mechanism(s) that melted (or partially melted) these objects operated multiple times over millions of years. The intensity of these events was highly variable. The major assumption 

Refractory inclusions are a class of chondritic components that derive their classification in part from the fact that they are composed of some of the most refractory materials found in primitive planetary samples (Grossman 1972 MacPherson et al. 1988 Connolly 2005 Beckett et al. 2006). In meteoritics, refractory refers to the temperature at which materials condense or evaporate within the gaseous environment in the protoplanetary disk. Thus, refractory inclusions are composed of minerals that are among the first predicted to condense from a gas of solar or enhanced solar composition (Ebel 2006). Their abundance in chondrites can potentially range up to 15 vol%, although most appear to be only a few vol% (Grossman et al. 1988 Russell et al. 1998 Ebel et al. 2008 Hezel et al. 2008). 

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