Postglacial tectonics and palaeoseisic dislocation in the Kovda area (Kandalaksha Bay, eastern Fennoscandian Shield)

Abstract

The Kandalaksha Graben of the White Sea is one of the most active tectonic zones of the eastern part of the Fennoscandian crystalline shield. Active faults of the Kandalaksha Graben derive from the axial zone of the Paleoproterozoic mobile Lapland Granulite Belt and the Riphean paleorift system. The system of active faults limits the northern and southern sides of the Kandalaksha Graben. An important problem is the study of the paleoseismicity of this zone. Local late- and postglacial rock dislocations and shifts, which occur due to strong seismic effects in the Kovda area of Kandalaksha Bay of the White Sea, are considered in the present paper. We consider the signs which testify to the dynamic (seismic) impact on rocks. In our work it is shown that paleoseisic dislocations are developed much wider and cover more representative land areas than previously reported. The dislocation concentration is in the area of about 325 km2. This area is the supposed epicenter of ancient seismic events that occurred repeatedly at the end of the Late Pleistocene and during the Holocene. According to radiocarbon analysis and the time of the opening of the seismic gorge, the age of the seismic event was determined about 7060 ± 160 yr cal BP. It has been established that disturbances of rocks are predominant seismogravitational and seismic vibrational types. They are formed by earthquakes of intensity > VIII degrees on the MSK-64 scale. Paleoseismic dislocations are localized in zones of active lineaments as well as confined to contacts of rocks of different petrographic composition. The directions of active fractures coincide with the strike of fracture in the fault scarps and gorges. This predetermines their seismic activation in the Late Pleistocene and Holocene. The main seismogenic fault is probably the fault-shift of young Kolvitsky Graben. Smaller-scale faults are considered as secondary feathering faults.