Dynamic thermal episodes in the protosolar nebula: Development of models from observations on CAI's

Evaluation of earlier observations indicated that layered rims on coarse-grained Allende CAI's were possibly the result of partial melting by ablation/drag-heating and reaction of CAI exteriors with a gas or gases of non-solar composition. Bunch and Chang reported the common occurrence of thin, fine-grained, matrix-like bands that at least partially surround rims of CAI's. Although material in these bands in general appears to be similar to matrix, SEM observations show them to be dissimilar in volatile element content, mineral composition, and grain morphology. Moreover, they appear to be related in time of formation with rim development and Na-metasomatism of CAI's. Observations indicate a short-lived but intense heating episode followed by radid cooling as the mechanism responsible for these CAI features.