Continental rifting and porphyry-molybdenum occurrences in the oslo region, Norway

The overall structure of the Oslo rift-system can be viewed as the result of interference between a N-S trending Permian fault system and a regional NE-SW trending, Precambrian shear-zone. The rift system comprises four mutually opposed horst and graben structures in a centrosymmetrical arrangement. Igneous activity occurred only in two en echelon segments, both of which possess a notable symmetric distribution of rocks and structures around the central axis of the rift system. The axial zone is occupied by Cambro-Silurian sediments which have been intruded by major granite bodies. Extensive lava-plateaus occur on each side of this axial zone. The adjacent zones contain the most prominent cauldrons of province. Further away from the axis follows a zone of batholitic intrusions, emplaced as composite diapirs and plutonic ring complexes. Hornfelsed sediments and volcanics in narrow bands occur at the lateral borders of the province, possibly preserved as the result of marginal tectonics associated with batholith emplacement. The formation of the Oslo Rift system apparently reflects a passive continental rifting which was gradually succeeded by considerable igneous activity.