The Mathematics of Cation Diffusion and Exchange Between Silicate Minerals During Retrograde Metamorphism

摘要: Neighboring crystals of garnet and cordierite in metamorphic rocks at Phillipston, Massachusetts, are chemically homogeneous except near their common boundaries. Mg2+-Fe2+ exchange occurred across these boundaries during the waning stages Acadian orogeny. Fe2+ was transferred from to an equivalent number moles Mg2+ were cordierite. The compositional profiles elements adjacent two phases potential sources information regarding cooling rates retrograde metamorphism. equations governing interdif-fusion between a linear decrease temperature solved closed form. Although there adequate data for distribution coefficient cordierite, too little is known about diffusion constants ions critical range 675°C 475°C. No absolute values Phillipston can, therefore, be extracted measured composition profiles. We have used our model profiles, however, refine meager knowledge dependence coefficients. Furthermore, observed chemical uniformity all but rims permits calculation minimum value interdiffusion hence 100°C per million years rate This implies very abrupt ending orogeny accompanied by exceptionally high uplift area.