The early major structure and petrology of rocks in the Bamble Series, Søndeled-Sandnesfjord, Aust-Agder.

Abstract

The geology and major fold structures of part of the Bamble Series are described from an area near Risør, Aust-Agder (some 15 km SW of the Levang paragneiss dome). Major structures are shown to have formed prior to the intrusion of Sveconorwegian \"hyperites\" and seem to belong to the earlier Svecofennian orogeny. The subsequent Sveconorwegian tectonism modified the older structures and caused deformation around the newly intruded \"hyperites\". The Svecofennian complex consisted largely of supracrustals and granitic gneisses, including those of the Levang paragneiss dome, just south of Kragerø. Immediately southwest of this, major structures are complex and disordered due to the development of basement-cover tectonics during the Sveconorwegian orogeny, which affected an area stabilised locally both by this dome and by some of the larger hyperites. The Sveconorwegian metamorphism amphibolitised the hyperites, remobilised some granitic rocks (with late-stage pegmatites) and produced isolated ortho-amphibole rocks.