Relative role of dynamic pressure forces and viscous stresses in tectonically active transition zones of the Earth

This article shows the role of dynamic non–hydrostatic pressure forces and viscous stresses in asthenosphere of tectonically active transition zones from the continent to the ocean. We have studied zones of active tectonic processes in the lithosphere and the underlying mantle, affecting the lithospheric blocks, the day surface of the Earth and the boundaries of density inhomogeneities. We showed the predominant influence of viscous stresses on the formation of mantle diapers and often associated hydrocarbon deposits. In subduction zones, in which a large-scale descending convective flow descends into the upper mantle as a sinking hard lithospheric block. We studied forces that determine the angle of subduction, depending on the age of the lithosphere, the rate of subduction and the rheological properties of the mantle material. We applied the method of analytical thermodynamic modeling of the tectonic structure of the upper mantle (lithosphere, asthenosphere) in the transition zone from the continent to the ocean. We concluded that the relative role of dynamic pressure forces prevailed in zones characterized by horizontally elongated asthenospheric movements in the mantle, as it happened under extended oceanic lithospheric plates. The novelty of the research is connected with the conclusion that under lithospheric micro-plates and near their boundaries, the roles of dynamic pressure forces and viscous stresses are comparable. In the areas of thermal diapirs associated with subduction zones and often located in transition zones from the continent to the ocean, the role of viscous stresses prevails. Thermal diapirs in subduction zones sometimes lead to the formation of hydrocarbon deposits due to mantle degassing processes.