Petrography and geochemistry of granites in the Kongsberg area, south Norway

The calcalkaline granites in the Kongsberg sector of the Kongsberg-Bamble areas are considered on the basis of petrography and geochemistry to be three distinct bodies and are referred to as the Kongsberg, Helgevatnet and Meheia granites. The Kongsberg granite is characterized by rather low Rb (82 ppm), Th (3.78 ppm), U (0.99 ppm), Th/K (0.80), U/K (0.20) and high K/Rb (620), and is not considered to be of igneous (intrusive) origin. The Helgevatnet and Meheia granites are, on the bases of field relations and chemistry, considered to have formed essentially by crystallization from melts but at different times. Both granite bodies are characterized by marked depletion in potassium and appreciable increases in sodium and calcium in their contact zones with the Knute group amphibolite country rock.