Isotope fractionation of neon during stepheating extraction? A comment on 'Re-interpretation of the existence of a primitive plume under Australia based on neon isotope fractionation during step heating' by Gautheron and Moreira (2003)

Using a Rayleigh distillation fractionation model, we calculate that the maximum isotope fractionation potentially achievable is less than 5% during the early stages of gas release from a sample. Our calculation corrects the erroneous conclusions of Gautheron and Moreira (2003), who re-interpreted the plume-like neon isotopic compositions found in metasomatic apatite from a south-eastern Australian xenolith (Matsumoto et al., 1997) to be the result of Rayleigh-type isotope fractionation of originally MORB-type neon during stepheating gas extraction. We stress that the modelling of neon isotopic fractionation by Gautheron and Moreira (2003) is incorrect, and that the finding of a plume-like neon isotopic composition in the apatite by Matsumoto et al. (1997) remains a quite valid and robust conclusion.