Tectonic Features and Stages of Evolution of the Baltic–Mezen Shear Zone in the Phanerozoic, Northwestern Russia

Abstract—The general tectonic features of the Baltic-Mezen zone developed along the border of the Fennoscandian shield and the Russian Plate in the north of the East European platform, are considered. The geophysical remote methods and structural analysis were used. It has been established that the zone has a length of more than 1000 km with a width of 10–40 km and can be traced from the Gulf of Finland in the sub-latitudinal direction along the southern shores of the Lake Ladoga and the Lake Onega in the valley of the River Onega.The Baltic-Mezen zone is represented by a system of folds and faults, fracture zones and brecciation, complicating the complexes of the Archean–Paleoproterozoic basement and the Vendian–Phanerozoic cover. Throughout the zone, changes in the configuration and displacement of the axes of the magnetic anomalies are noted; on seismic sections, the systems of discontinuities penetrating the basement and cover complexes are decrypted. On the surface, the discontinuous structures of the zone are expressed in the various forms of relief, often violate and displace glacial morphostructures. Based on the analysis of materials on the nature of the paleoseismites distribution and surfaces of unconformity in the sediments of the cover, as well as the structural features of various rock complexes, a long period of development of the Baltic-Mezen zone was established during the Caledonian, Hercynian and the latest stages of deformation. The Caledonian stage was associated with the formation of paleoseismites horizons of Kukruz phase (~ 460 Ma), as well as the folded-fault structures formed in the Late Silurian–Early Devonian. The Hercynian stage was manifested by several seismic and tectonic events in the Late Devonian (Frasnian age), in the Early (Visean age) and Late (Kasimovian century) Carboniferous. The newest stage was associated with Neopleistocene glaciodynamic processes and two stages of seismic events in the late and post-glacial period, which were accompanied by activation of ancient faults and local development of folded structures. The developed scale of paleoseismic and deformation events of the Baltic-Mezen zone can be used for tectono-dynamic reconstructions based on additional analysis of materials of structural-kinematic research.