Isotope fractionation in silicate melts by thermal diffusion

Arising from F. Huang, P. et al. Nature 464, 396–400 (2010)10.1038/nature08840 ; Huang et al. reply It was recently shown that relatively large (compared to analytical precision) steady state thermal isotope fractionations are produced in silicate melts whenever temperature differences are maintained for a sufficiently long time1,2. Huang et al.3 reported new data on thermal isotopic fractionation of magnesium, calcium, and iron in silicate liquids, and claimed (1) that thermal isotopic fractionations in silicate liquids are independent of composition and temperature, and (2) that their “results lead to a simple and robust framework for characterizing isotope fractionations by thermal diffusion in natural and synthetic systems”. Here I consider whether the data and arguments presented by Huang et al.3 support their claims. In summary, I caution against assuming (on the basis of the data presented by Huang et al.3) that the thermal isotopic fractionations are independent of temperature and composition, or that a framework of the type claimed has been found.