Abstract
Low-grade metamorphic minerals have been found within the high-grade terrain in the Bamble sector, SE-Norway. The minerals prehnite and pumpellyite indicative of prehnite-pumpellyite facies conditions have been confirmed around the Kragerø area. The formation of analcime, thomsonite, hydrogarnet, albite and clay minerals is also a part of the low-grade metamorphism. The occurrence of these low-grade minerals is constricted to pseudomorph replacement of earlier mineral phases, hydrothermal veins and characteristic mineral lenses within biotite. The replacement reactions include replacement of: plagioclase by prehnite, albite by prehnite and scapolite by analcime. The occurrence of prehnite and albite together in veins indicates that a late metasomatic albitization occurred in the area. Swelling textures in the form of mineral lenses in biotite is common in rocks containing biotite. The force of crystallization is suggested to be an important mechanism during the formation of these swelling textures leading to a deformation of biotite and increased fracturing of neighboring grains. This process facilitates the fluid infiltration through the rock volume.
Low-grade metamorphic minerals have been found within the high-grade terrain in the Bamble sector, SE-Norway. The minerals prehnite and pumpellyite indicative of prehnite-pumpellyite facies conditions have been confirmed around the Kragerø area. The formation of analcime, thomsonite, hydrogarnet, albite and clay minerals is also a part of the low-grade metamorphism. The occurrence of these low-grade minerals is constricted to pseudomorph replacement of earlier mineral phases, hydrothermal veins and characteristic mineral lenses within biotite. The replacement reactions include replacement of: plagioclase by prehnite, albite by prehnite and scapolite by analcime. The occurrence of prehnite and albite together in veins indicates that a late metasomatic albitization occurred in the area. Swelling textures in the form of mineral lenses in biotite is common in rocks containing biotite. The force of crystallization is suggested to be an important mechanism during the formation of these swelling textures leading to a deformation of biotite and increased fracturing of neighboring grains. This process facilitates the fluid infiltration through the rock volume.