En petrografisk-mineralogisk undersøkelse i området syd for Majavann, spesielt granaters sammensetning under regional metamorfose.

Abstract

The investigated area is situated in the Norwegian Caledonian orogenic belt, south of Majavann (Nordland county). The main rock types are micagneisses and garnet-mica-schists, cristalline limestones, granodioritic-gneisses, amphibolites, tremolite-schists, periodotite, trondhjemite and light coloured granodiorite. The classification of Turner & Verhoogen (1960) is used. Both rocks of sedimentary and magmatic origin are regionally metamorphosed during the Caledonian orogeny. In the amphibolites, the plagioclases, which are in equilibrium with epidote, show an increasing An-content from west to east. It is highly possible that this indicates an increasing degree of metamorphism (fig. 7). It is concluded that a lower almandite-amphibolite facies metamorphism is valid for the investigated area. A more detailed subdivision based on the mineral paragenesis of the rocks is not possible. Anexception is presented by the staurolite-bearing garnet-muscovite-schist. An extensive investigation of the garnets has been carried out as it is believed that their composition is dependent on the degree of metamorphism. Thus a finer subdivision of metamorphic facies seems to be possible. The methods followed are described, and the results of the measurements are discussed.