Les gneiss oielles de la region de Vegårshei-Gjerstad (Norvege Meridonale) I. Etude petrographique

Two elongate bodies of augen gneisses from south of Vegårshei to north of Gjerstad occur in the Precambrian basement of southern Norway on either side of the ' Great Breccia' which represents the boundary between the Bamble and Telemark provinces. Petrographical studies have established a striking similarity between these two bodies of augen gneisses: most augen gneisses hold large (up to 10 cm) porphyroblasts of potash feldspars, some may contain porphyroblasts of plagioclase or even amphibole. Moreover, at the southern end of the Vegårshei body, the augen gneisses grade into a dark orthopyroxene- and orthoclase-bearing augen gneiss having clear charnockitic affinities. From field and thin section observations, it is inferred that the charnockitic augen gneisses are equivalent to normal augen gneisses having suffered a local metamorphism in the hornblende granulite subfacies.