An experimental study of Mg self-diffusion in spinel

Mg isotope heterogeneity, both between coexisting spinel and silicates and among spinels, is a prominent feature of Plagioclase-Olivine Inclusions (POIs) (1). The preservation of isotopic heterogeneity and relict spinel (Sp) in inclusions with igneous textures indicates that the thermal event which partially melted the precursor material either had too low a temperature or was too brief to allow Mg isotope homogenization between Sp and the melt. Since the temperature history required to homogenize Mg isotopes depends on the diffusion rate of Mg in Sp, we designed experiments using an isotope tracer method to determine this critical rate (2).