Replacement of graphic pegmatite by graphic albite-actinolite-clinopyroxene intergrowths (Mjavatn, southern Norway)

After peak metamorphism, the Sveconorwegian orogen in the Bamble sector, so uthern Norway, underwent three separate events, viz., the intrusion of gran itic pegmatites, regional but locally acting metasomatism. and, finally, in trusion of post-tectonic granites. Metasomatism resulted in localized but w idespread formation of albite-actinolite/clinopyroxene-quartz assemblages, with associated monomineralic veins of actinolite, Ti-minerals, etc. At one locality. the Mjavatn pegmatite, graphic quartz-K-feldspar intergrowths we re replaced by graphic albite-actinolite-clinopyroxene intergrowths. The pr eservation of the graphic texture, implying conservation of volume, enables quantification of mass transfer: Application of Gresens' composition-volum e relationships of metasomatism (isocon diagrams) demonstrates massive infl uxes of Al, Na, Ca, Mg and Fe, accompanied by removal of K and, to a lesser extent, Si. Fluid inclusion studies demonstrate that NaCl-rich brines are the most likely candidates to transport the observed mass. Metasomatism is estimated to have occurred at 350-450 degreesC. 2-4 kbar.