Structure, Rheology, Petrology, and Geodynamics of the Tectonosphere of the Sea of Japan

The geological-structural, magmatic, seismic, and thermometric models of the Earth’s crust and upper mantle of the Sea of Japan region are considered in relation to three-dimensional rheological gravity models reflected in horizontal and vertical sections of density contrast of the tectonosphere. In the crust and the upper mantle, formal manifestations of a right-lateral strike-slip duplex were found, in association with rift-related extension zones and central vortex structures. In the central regions of the Sea of Japan, a mushroomlike low-viscosity zone of typical of plumes is mapped in the depth interval of 60–200 km. The gravity models show signs of Late Cretaceous subduction of the Pacific Plate under the continental margin and Eocene–Oligocene subduction of this plate under the Japanese island arc. The Pacific lithosphere is split into crustal and lower lithospheric plates. The depth and thickness of rigid crustal and lithospheric plates have been estimated, faults of which are observed in rift-related extension zones. Petrochemical analysis of volcanic rocks dredged from the floor of the Sea of Japan confirms the existence of two extension stages, accompanied by volcanism of an initially postsubduction (ACMB), then spreading (N-MORB) and postspreading plume (OIB) nature.