THERMAL HISTORIES OF CO3 CHONDRITES - APPLICATION OF OLIVINE DIFFUSION MODELING TO PARENT BODY METAMORPHISM

The petrologic sequence observed in the CO3 chondrite group has been suggested to be the result of thermal metamorphism on a parent body. We have developed a model to examine the possibility that chondrule and matrix olivines equilibrated in situ, during parent body metamorphism. The model considers Fe-Mg interdiffusion between chondrule and matrix olivines. Zoning profiles comparable to those observed in chondrule olivines from partially equilibrated members of the series are reproduced successfully. Metamorphism of CO3 chondrites on a parent body is therefore a viable model for the observed equilibration. Results indicate that peak metamorphic temperatures experienced by the CO3 chondrites were around 500-degrees-C, and that the range of peak temperatures between unequilibrated and equilibrated subtypes was relatively narrow, around 100-degrees-C.