Fred Gaidies

Abstract

Understanding the origin of rock microstructure is critical for refining models of the geodynamics of the Earth. Based on the compositional growth zoning of a population of garnet crystals in a mica schist from the Sikkim Himalaya, I will present a model that can be used to gain quantitative insight into (1) the relative growth rates of individual crystals, (2) the departure from equilibrium during their growth, and (3) the mobility of the porphyroblast-matrix interface. Results of this model indicate that the driving force for garnet growth was exceedingly small and is comparable in magnitude to the interfacial energy associated with the garnet-matrix interface. This caused size-dependent garnet growth at macroscopic length scales, with a decrease in radial growth rates for smaller crystals due to the penalty effect of the interfacial energy. This research highlights the fundamental importance of interface properties for the microstructural evolution of petrological systems close to equilibrium.