Petrography and metamorphism in the Precambrian rocks of the Magnor area, S. Norway.

Abstract

The rocks of the Magnor area comprise various red and grey gneisses, amphibolites and red, unfoliated granites. The gneisses and amphibolites most probably were sediments and basic intrusives, respectively, metamorphosed by regional metamorphism in the uppermost part of the almandine-amphibolite facies. Some features are reminiscent of granulite facies rocks, as for instance abundance of antiperthitic feldspar in the gneisses. The red granites were formed subsequently to the main metamorphism, probably by potash metasomatism acting on the gneisses. An episode of folding separates the regional metamorphism from the formation of the red granites. Retrograde metamorphsim is related to the socalled \"mylonite zone\" and is resticted to the easternmost gneiss areas. By analogy with relations on the Swedish side of the border the rocks of the Magnor area are to be considered as Pre-Gothian in age.