U-Pb Dating of Zircon from the Svecofennian Plagiogranite Intrusion, Baltic Shield: Specific Features of the Upper and Lower Intercepts

摘要

Svecofennian orogeny within the Baltic Shield occurred 2.0-1.7 Ga B.P.. The beginning of this stage was marked by the initiation of oceanic and marine basins with large-scale accumulations of volca-nosedimentary rocks. After a short time, sedimentation was replaced by plutonic and metamorphic activities. Processes of metamorphism were characterized by intense heat flows and the development of mineral assemblages of low- and moderate-pressure (up to the granulite facies). This is exemplified by the Ladoga andalusite-sillimanite type metamorphic complex. Similar Svecofennian complexes occur in the adjacent regions of Finland and are traced in Sweden. Further westward of Sweden, Svecofennides are overlain by Caledonian allochthon and are exposed only in tectonic windows in Norway.