Homogenization of high-T garnets during deformation, fluid flow and metasomatism Catalonian Coastal Ranges, NE Iberian Peninsula

Abstract

Progressive homogenization of previous growth zoning patterns in garnets of the HT/LP sillimanite zone of the Osor complex (NE Iberian Peninsula) is interpreted as the product of intracrystalline diffusional processes plus the operation of open system reactions coupled to fluid flow. The infiltrated fluid evolved during syn-tectonic emplacement and crystallization of two-mica peraluminous leucogranitoid sheets. The flow began in a more or less pervasive regime, then the fluid phase became progressively saturated in Si and K–Na species as well as progressively focused along schistose domains subparallel to the developing crenulation cleavage planes. A sequence of open system processes related to this fluid flow took place along the schistose domains syn- to late-tectonically: quartz leaching and further deposition in veins, extreme fibrolitization, muscovite+high Na/Ca plagioclase+biotite blastesis and homogenization of previous garnet growth zoning profiles. Notably the growth profiles have been preserved only in the less permeable quartz-rich, muscovite and plagioclase poor, semi-pelitic geissic domains.