The Precambrian metamorphic rocks of the Nissedal supracrustal series, a thick sequence of basic and acidic lavas with associated agglomerates, has been intruded by gabbroic rocks and then been metamorphosed to amphibolite and epidote amphibolite grade by two periods of regional metamorphism. During the metamorphism, basic lavas were converted into amphibolites and the acidic lavas into leptites. The gabbro and its associated pegmatitic phase were metamorphosed to hyperite and ödegårdite respectively. Extensive granitisation accompanied the second metamorphic event causing large amounts of the supracrustal rock to become converted into granite-gneiss. Lesser amounts of banded gneiss, hornblende gneiss and migmatite were also formed from the supracrustal rocks at this time. The occurrence of lamprophyre dykes of Permian( ?) age is noted and the Söftestad iron ore deposit is briefly described.
The precambrian rocks of the Telemark area in south central Norway