Geological evolution of the karelian granite-greenstone terrain

Abstract

Abstract The Karelian craton ( > 2.3 Ga ) has been recognized within the Baltic Shield. The basement of the craton is a late Archaean granite—greenstone terrain. The greenstone belts from different regions of Karelia show variations in age and composition of volcanic rocks. Two older belts ( > 2.9 Ga ) - one with multimodal volcanism and the other with bimodal volcanism - constitute the eastern part of the terrain (central and eastern Karelia). Two younger belts (2.8–2.6 Ga) with the same modal distributions of volcanic rocks make up the western part of the terrain (western Karelia and eastern Finland). According to magnetic anomaly patterns there are four types of granite—gneiss areas that separate the greenstone belts. Three types represent the greenstone basement reworked at different degrees. The fourth type corresponds to tonalites and granites surrounding the greenstone belts. The emplacement and evolution of the tonalites and granites are related to the evolution of the greenstone belts. Geochronological data on the granites of the basement demonstrate a decrease in age from E to W. Late Archaean low-pressure granulite metamorphism took place almost synchronously (2.65 Ga ago) in both the western and eastern domains.