On some quartz-plagioclase veins in the Connemara schists, Ireland

Abstract

SummaryQuartz-plagioclase veins in staurolite schists often have margins depleted in the vein minerals. In some cases vein formation has simply involved recrystallization of groundmass grains into large vein grains in a closed system. The driving force for this process is reduction of strain energy and surface free energy. It is suggested that the veins initiate when grain boundaries have been opened up by hydraulic fracturing during medium grade metamorphism. The segregation process can be explained by a model of local equilibrium between grains and a continuous pore fluid similar to that commonly applied to metasomatic reactions; however, no phase change occurs.