Crystallization of magmatic iron meteorites: The role of mixing in the molten core

The IIIAB group is the largest of the magmatic iron meteorite groups and co nsequently is commonly used to test models of asteroid core crystallization . Simple fractional crystallization calculations appear to reproduce the ge neral shape of the elemental trends observed in the IIIAB group when these trends are plotted vs. Ni, as is traditionally done. However, when the elem ental trends are examined vs. another element (such as Ge vs. Ir), simple f ractional crystallization fails to match a significant portion of the trend , specifically meteorites formed during the final stages of crystallization . Our simple mixing model, which attempts to account for the possibility of inhomogeneities in the molten metallic core, is able to reproduce the enti re IIIAB trend observed. This model is a variant of simple fractional cryst allization and involves mixing between a zone of liquid involved in the cry stallization process and a second zone too far from the crystallizing solid to be actively involved in crystallization. This model does not suggest on e unique solution for the method by which an asteroidal core crystallizes; rather it demonstrates that including the effects of mixing in the molten c ore can account for the observed IIIAB elemental trends, particularly the l ate-stage crystallizing members, which other models have difficulty explain ing.