Genetic Relationships between Chondrules, Fine-grained Rims, and Interchondrule Matrix

Chondrules, fine-grained rims on chondrules and CAIs, and fine-grained matrix are three major components of chondritic meteorites. In this chapter, we attempt to evaluate the potential genetic relationships between these components. We show that in order to evaluate possible genetic relationships, it is necessary to understand and control for the effects of parent body processing and secondary processes in the nebula. The meteorites best suited for this type of study are CO3.0, CR2, LL3.03.1, and some ungrouped chondrites such as Acfer 094 and Adelaide. We review petrographic, mineralogical, and compositional data for matrix and fine-grained rims and compare their characteristics to those of chondrules and bulk meteorites. Evidence is presented that can be interpreted to indicate that for each meteorite class, precursors for chondrules and matrix were exposed to the same thermal processing in the nebula and that chondrules and matrix are closely related. However, the evidence can also be interpreted in other ways that do not require a close relationship. We find that chondrules almost certainly lost volatiles through evaporation when they formed, but it is difficult to demonstrate the degree of loss. It is also difficult to determine the level to