Original paper

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

Nijland, Timo G.; Touret, Jacques L.R.

Abstract

After peak metamorphism, the Sveconorwegian orogen in the Bamble sector, southern Norway, underwent three separate events, viz., the intrusion of granitic pegmatites, regional but locally acting metasomatism, and, finally, intrusion of post-tectonic granites. Metasomatism resulted in localized but widespread formation of albite-actinolite/clinopyroxene-quartz assemblages, with associated monomineralic veins of actinolite, Ti-minerals, etc. At one locality, the Mjåvatn pegmatite, graphic quartz-K-feldspar intergrowths were replaced by graphic albite-actinolite-clinopyroxene intergrowths. The preservation of the graphic texture, implying conservation of volume, enables quantification of mass transfer. Application of Gresens' composition-volume relationships of metasomatism (isocon diagrams) demonstrates massive influxes 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°C, 2-4 kbar.

Keywords

metasomatismalbite-actinolite-quartz rocksnacl-brinesgraphic pegmatitebamblenorway