On the ages of some granitoid and schist complexes in northern Finland

Abstract

Contact observations and most radiometric datings indicate that the large complex of granitoid rocks and migmatites in Central Lapland is late Svecokarelian (Proterozoic) in age. The geological setting of the complex suggests, however, that it previously formed the basement for the Proterozoic sedimentation and a source of some of the sedimentary material. About 1800 Ma ago it apparently underwent partial anatexis, especially near the Proterozoic schist belts. The concept that some parts of the schist areas of Kuusamo, Salla and Central Lapland are of Archean age is disputable. The Salla schist area, which some authors maintain is an Archean greenstone belt, is obviously Proterozoic in age. U-Pb ages reported for zircons, titanites and monazites from granitoid rocks from six localities in Kuusamo, Salla, Kemijärvi and Rovaniemi areas range from 2738 Ma to 1770 Ma.