Textural coarsening in igneous rocks

Abstract

The initial growth of crystals in magma is driven by kinetic forces, and the resulting textures can be preserved in rapidly cooled igneous rocks. However, crystals in such rocks have a high surface area with respect to their volume, and hence an excess surface energy. This energy can be dissipated by textural equilibration. At advanced stages, this is represented by textural coarsening, in which smaller crystals dissolve simultaneously with the growth of larger crystals. These textural changes occur commonly in slowly cooled plutonic rocks and may be important for the development of some volcanic rocks as well. Textural coarsening is clearly an important petrologic process, but may not have received the attention it deserves inasmuch as it does not change the chemical composition of the rock, and hence cannot be quantified by the geochemical methods that currently dominate petrology.