Metamorphism as Garnet Sees It: The Kinetics of Nucleation and Growth, Equilibration, and Diffusional Relaxation

摘要: Garnet bears witness to the importance of kinetics during metamorphism in its microstructural features, compositional zoning, and diffusional response thermal events. Porphyroblastic textures carry quantitative signals protracted nucleation sluggish intergranular diffusion, key impediments reaction progress that may result crystallization under conditions well removed from equilibrium. Growth zoning garnet reveals partial chemical equilibration with matrix minerals: transport keeps pace growth for some elements but not others, leading variable degrees length scales equilibration. Partial relaxation by intracrystalline diffusion is a sensitive indicator history, constraining rates timescales peak metamorphic heating, processes burial exhumation, retrogression on cooling.