Crystallization of calcium-aluminum-rich inclusions: Experimental studies on the effects of repeated heating events

The observed textures and chemistry of calcium-aluminum-rich inclusions (CA Is) are presumed to be the culmination of a series of repeated heating and cooling events in the early history of the solar nebula. We have examined t he effects of these heating/cooling cycles experimentally on a bulk composi tion representing an average Type B CAI composition by varying the nature o f the starting material. Although the most recent and/or highest temperatur e event prior to incorporation into the parent body dominates the texture a nd chemistry of the CAI, prior events affect the phase compositions and tex ture. We have determined that a prior low-temperature event (simulated by h eating the sample to 1275 degrees C and cooling slowly) increases the likel ihood of anorthite crystallization in subsequent higher temperature events. A prior high-temperature event that produced dendritic melilite,(simulated by heating the sample to 1550 degrees C and cooling rapidly) results in me lilite that shows evidence of rapid crystallization in subsequent lower tem perature events. The addition of Pt powder to the starting material appears to enhance the ability of anorthite to nucleate from this composition and increases the number of melilite crystals present in samples that crystalli ze euhedral melilite.