A Simple Thermodynamic Model for Grain Interfaces: Some Insights on Nucleation, Rock Textures, and Metamorphic Differentiation

Abstract

By assuming that all grain interfaces may be approximated by a mosaic of planar elements, it is possible to obtain certain relationships that should, within the validity of the model, characterize an equilibrium texture. These include "Wulff's Law" for ,the equilibrium form of a crystal in a fluid, and also a rule of indentation that has features in common with Becke's concept of a "crystalloblastic series." The model also leads to simple expressions relating the critical size of new crystal nuclei to the activation energy for nucleation. Disequilibrium textural features are of special interest because each carries with it a historical message. Disequilibrium textures may also provide the driving forces for the material transfers that lead to certain types of metamorphic differentiation. Metamorphic differentiation, however, may also arise through the selectively localized nucleation of new porphyroblasts or may be modified by kinematic effects.