Porphyroblast crystallization: linking processes, kinetics, and microstructures

Analysis of the processes, kinetics, and microstructures that characterize porphyroblast crystallization identifies the primary factors that govern the progress of metamorphic reactions and highlights the importance of feedbacks among those factors. Commonly, the kinetics of nucleation and the kinetics of intergranular diffusion are rate-limiting in porphyroblast crystallization. That finding should inspire petrologic vigilance, as it implies strong potential for significant thermal overstepping of reactions, crystallization at high levels of chemical affinity, reactions that span protracted intervals of time and temperature, and limited length scales for chemical equilibration.