Mechanisms of metasomatism and metamorphism on the local mineral scale: The role of dissolution-reprecipitation during mineral re-equilibration

Abstract

© Springer-Verlag Berlin Heidelberg 2013. Metamorphism and metasomatism both involve the re-equilibration of mineral assemblages due to changes in pressure, temperature and/or chemical environment. Both processes involve material transport but on different length scales, and therefore every metamorphic reaction is metasomatic on a local scale. Fluids provide a transport mechanism which is orders of magnitude faster than solid state diffusion and induce re-equilibration through dissolution of parent phases and reprecipitation of products. This chapter deals with some of the questions related to such processes, including the mechanisms of fluid transport through low permeability rocks, how coupling between dissolution and precipitation retains the volume of a rock during metamorphism and metasomatism, and how textural criteria are used to define mechanisms of reactions. These issues are illustrated by examples taken from experiments as well as reactions in nature including a review of some aspects of the transformation of aragonite to calcite, the albite to jadeite + quartz reaction, albitization, the origin of compositional zoning and inclusions in apatite, garnet replacement textures during eclogitization and the reaction mechanisms that produce corona textures. The chapter ends with a summary of the mechanism of pseudomorphic replacement by interface-coupled dissolution-precipitation.