Precambrian migmatites representing a 4-5 km thick series of metasediments, amphibolites, banded gneisses, and granodioritic (quartzmonzonitic) gneisses were deformed at a deep level of the earth's crust and shaped into a great antiform structure plunging towards NE. A second deformational phase along SSE-NNW axis is connected to intrusions of granitic pegmatites. The banded gneisses may be of supracrustal origin with some anatectic layers. A few amphibolites are supposed to be of volcanic origin, while others certainly were marly limestones. The granodioritic gneisses are most probably of anatectic origin. The rocks have been subjected to amphibolite facies metamorphism, and there is correspondence between modes and mesonorms calculated from 10 chemical analyses.
Geological investigations in the precambrian of Southern Norway 1. The complex of metasediments and migmatites at Tveit, Kristiansand.