Anisotropy in Mg isotopic fractionation during evaporation of forsterite in vacuum

Abstract

Surface Mg isotopic compositions of forsterite, evaporated in vacuum at 1504-1786^oC, were measured by ion microprobe in order to investigate anisotropy in isotopic fractionation during evaporation. The degree of Mg isotopic fractionation of evaporated forsterite is the largest for the (001) surface and the smallest for the (010) surface at the range of experimental temperatures, showing anisotropy of isotopic fractionation. The isotopic fractionation factors between ²⁶Mg and ²⁴Mg at 1692^oC, which were obtained using a diffusion-controlled isotopic fractionation model during evaporation, are 1.028, 1.023 and 1.017 for the (001), (100) and (010) surfaces, respectively.