The Precambrian rocks of Norway belong to what is known as the Fennoscandavian Shield. On a regional scale, the bedrock geology can be divided into areas that have a shared history of volcanism, deformation, and the formation of large mountain chains that eventually became worn down through the erosion and sedimentation (see map).
The oldest rocks of the Fennoscandian Shield are found in the northern Finland and in the Kola peninsula, and are called archaic gneisses (over 2500 million years old). With these are found paleoproterozoic rocks (2500-1950 million years) that are comprised of thick volcanic and sedimentary layers deposited in the rift zones of the archaic basement.
To the south west, we find the areas where the formation of the Earth's crust occurred c . 1950-1750 million years ago. Deformation and transformation led to the formation of the Sveconorwegian mountain chain that extends through the central parts of Sweden and Finland.
The Svekofenniske area is demarcated in the west by the Transscandinanavian igneous belt. This area is comprised mostly of granitic basement rocks that stretch along a 1500 km long zone from southern Sweden to the Lofoten Islands.
In the southern Norway, and southwest Sweden, the bedrock geology has been formed over a long time (ca 1750 to 900 million years ago). Here we have a wide selection of rocks which are the remnants of two important mountain chains: the Gothian (1700-1500 million) and the Sveconorwegian (about 1130-900 million years).
The Caledonian orogeny was formed about 400 million years ago. Large rock sheets were then thrust from the Northwest to the Southeast and now lies as a blanket, located over the older rocks along the western part of Scandinavia.
Younger volcanic and sedimentary deposits composed of basement rocks can be found in the Oslo region. These were formed along a permian rift structure in the bedrock in Eastern Norway.