Geophysical Fields and Geodynamics of Eastern Chukotka

The geology of Chukotka peninsula is one of the most important problems in Beringia development. The absolute age of some lithological assemblages, with the preservation of their composition, was changed by modern studies. This has resulted alternat explanation of geological development of some structures. For examples, for metamorphic assemblages, it is supposed that they have occurred as a result of tectonic activity and elevation to the surface of rocks warmed at the depth. This processes was synchronous with the formation of the Okhotsk-Chukotka volcanogenic belt (OCVB) The study of the deep composition by the geophysical methods should stimulate the knowledge of geological development of the Eastern Chukotka. The anomalous magnetic field of Chukotka peninsula is correlated by geological occurrences. Outcrops of sedimentary and metamorphic rocks, granitoid intrusions correspond to the calm, close to normal magnetic field. Within intrusion and at their boundaries, small in area, high gradient anomalies, associated with dikes of basic composition and zones of contact metamorphism, are observed. Zons of intensive linear anomalies are traced above the Kolyuchin-Mechigmen riftogenic depression. They are result of presence of high magnetic subvertical bodies of the ultrabasic composition of Triassic age. These anomalies are also traced in the Bering Sea. The rocks of OCVB, mosaic magnetic field with smoll isometric or ellipsoidal anomalies occur. The ultrabasic rocks of Triassic age occur in the gravity field by the local positive Bouguer anomalies up to +40 mGl. To the south from Kolyuchin Bay, their thickness reaches 10 km. In the region of the Mechigmen Inlet their thickness does not exceed 2.5-3 km. Probably ultrabasic rocks of the same thickness are located in the region to the north-east of the Kolyuchin Bay coast. The outcrops of granitoid intrusions are marked by negative anomalies of up to -20 to -25 mGl. The field character makes it possible to suppose that at depth, most of them are combined, and form the line of mass, large in area. Sedimentary deposits of Paleozoic correspond to the small ( up to +10 - +15 mGl) anomalies. Metamorphic domes are marked by small negative anomalies, that are composed of great minimum, associated with granitoid. Poorly negative gravity field, complicated by anomalies that are associated with granitoid, are observed above the rocks of OCVB. The regional gravity field of the Chukotka peninsula along the coastal is positive ( up to 10 mGl), but within the land , it is negative (up to -15 mGl). It is explained by the fact of post-glacial rebound after the melting of glacier falling into the Bering sea. This fact is testified by the rise of the Chukotka Sea coast. It is possible, that the line of earthquakes, having the spreading mechanism, is related to these processes. Minimum zones correspond to the regions of the largest seismic activity in the field of velocity of longitudinal and cross seismic waves. The analogous geodynamic environments are observed on the Scandinavia peninsula.