Replacement Processes in the Earth’s Crust

A fundamental question in metamorphism is: What is the mechanism that converts one mineral assemblage into another in response to a change in the physical and/or chemical environment? The fact that aqueous fluids must be involved in such large-scale re-equilibration has been demonstrated by petrological, mineralogical, micro-structural and isotopic data. Fluid–mineral reactions take place by dissolution–precipitation processes, but converting one rock into another requires pervasive transport of reactive fluid through the entire rock. The generation of reaction-induced porosity and the spatial and temporal coupling of dissolution and precipitation can account for fluid and element transport through rocks and the replacement of one mineral assemblage by another.