Evaporation/condensation of Chondritic Chondrule Precursors in Nebular

Introduction: The origin of chondrules remains one of the great enigmas in meteoritics. Under the canonical formation conditions of low pressures, high temperatures and moderate cooling rates (10-1000 K/hr), some evaporation at least of the moderately volatile elements is expected. Chondrules are depleted in moderately volatile elements, but they do not have the systematic isotopic fractionations that should characterize evaporation under nearly Rayleigh conditions. One possible explanation for the chondrule compositions is that while they did experience evaporation, they were able to approach equilibrium with the evaporated gas at high temperatures and these compositions were frozen in by crystallization and sluggish diffusion in the residual melt during cooling. Shock heating is currently the most favored mechanism for heating chondrules. Here we report a preliminary study of the elemental and isotopic evolution of chondritic chondrule precursors during shock heating Shock and evaporation models: The shock models used here are described in detail by [1]. For this initial exploration of shock heating, a simple prescription was used for evaporation evaporation was only assumed to occur when dust/chondrule temperatures exceeded 2000 K, and what evaporated was assumed to have the composition and vaporization enthalpy of forsterite.