A vaporization model for iron/silicate fractionation in the Mercury protoplanet

A study has been carried out on the vaporization of a totally molten silicate magma of chondritic composition heated into the range 2500-3500 K. The motivation for this was to determine the changes in the composition of the mantle that would occur in the Mercury protoplanet should that body have been subjected to the high-temperature phase in the evolution of the primitive solar nebula, but the results are of more general interest. An empirical model based on ideal mixing of complex components was used to describe the nonideal magma. It is found that vaporization of about 70-80 percent of the original amount of silicate from a chondritic planet is required to produce an iron-rich body with a mean uncompressed density equal to that deduced for Mercury. At this point the silicate is depleted in the alkalis, FeO, and SiO2, and enriched in CaO, MgO, Al2O3, and TiO2 relative to chondritic material.