Key concepts in interpreting the concentrations of the rare earth elements in zircon

Abstract

Because of the great potential for zircon to provide insights into crustal melting and evolution, much work has been done to develop tools to interpret its trace element concentrations. There are several complexities to zircon/melt partitioning that appear to be underappreciated, and these are illustrated using a combination of new and existing data. First, sector zoning causes significant dispersion in the population of zircon compositions even for those grown from a homogeneous melt. Second, many analyses of natural crystals contain trace elements at unrealistic concentrations: there are multiple potential sources for this apparent contamination. Third, new experimental data show that Henry's Law is obeyed by rare earth elements in zircon, despite recent suggestions to the contrary. Fourth, zircon/melt partition coefficients are functions of temperature, melt composition and in some cases oxygen fugacity, rather than being constants.