Post-folding magmatism (1.85–1.7 Ga) in the eastern part of the Baltic Shield: Correlation of its structural position and evolution of surrounding complexes

Abstract

This work discusses the structural and compositional correlation of an unusual group of rocks that comprise post-folding massifs and dikes in the eastern Baltic Shield, which formed between 1.85 and 1.7 Ga. Occurring from the Barents Sea in the north to the Gulf of Finland in the south, these structures are associated with areas of granulite facies rocks that formed under conditions corresponding to the deep continental crust. Large-scale extension of continental crust, which led to the exhumation of the granulite complex, simultaneous with the formation of metasomatic formations and manifestations of post-folding magmatism, was confined to the periphery of a large circular structure, which is interpreted by us as the Baltic nucleus, or a tectonic portion of the continental crust at the end of early Precambrian. The formation of enriched mantle, a source of the Paleozoic alkaline melts, can also be associated with these processes of extension.