Oswald Ripening of Ca-rich Pyroxene. Implication on the Very Late Cooling History of Chondrule Mesostasis

Introduction: Knowledge of how crystals grow is of fundamental importance for interpreting textures observed in meteorites. However, data on crystal growth of rock-forming silicates for a very small degree of undercooling (< 1°C) are extremely rare. Recently [1], it was demonstrated that these very small degrees of undercooling could be experimentally approached by studying the kinetic of Oswald ripening if this kinetics is not controlled by diffusion. Then, mechanisms and rates of crystal growth of olivine, plagioclase and quartz have been determined [1,2]. The present experimental study was undertaken to investigate growth kinetic of pyroxene at small undercooling. The objective is two fold: (i) determining the diopside growth mechanism, (ii) obtaining quantitative data on the rate of diopside crystal growth. Experimental techniques: Ostwald ripening experiments are generally conducted with a starting material that is a mixture of crystal powder and glass. In the present study, a particularly of diopside growth is used to develop a non-conventional method to investigate Ostwald ripening. Indeed, it is well known that diopside crystals, but also most of clinopyroxene, grow very quickly with a dendritic habit when a glass is reheated. Experimental protocol used in this study takes advantage of this rapid growth of clinopyroxene during the reheating step. Thermal procedure used in this study is represented figure 1.