Speed structure of the mantle under the Dnieper-Donets Depression and its surroundings. Part I

• Дата: 2020
• Автори: Tsvetkova, T.A., Bugaenko, I.V., Zaets, L.N.
• Формат: Стаття
• Мова: Російська
• Опубліковано: S. Subbotin Institute of Geophysics of the NAS of Ukraine 2020
• Теми: three-dimensional P-velocity model; mantle; Dnieper-Donets Depression; horizontal sections; velocity regions
• Онлайн доступ: https://journals.uran.ua/geofizicheskiy/article/view/201742
• Назва журналу: Geofizicheskiy Zhurnal

The article discusses the high-speed structure of the mantle under the Dnieper-Donets Depression (DDD). The solution obtained by the Taylor approximation of the solution of the three-dimensional seismic tomography problem is used. The method is independent of the reference model and gives a better approximation of nonlinearity with respect to the classical solution. The resulting 3D P-velocity model of the mantle is presented in the form of horizontal and vertical sections. Horizontal sections were obtained with a step of 25 km at «true speeds». Vertical sections, longitude and latitude, are shown with a step of 1° in the form of residuals of velocities relative to the generalized average velocity under the mantle of Eurasia and its environment. This paper presents horizontal sections. It is shown that the occurrence of DDD can be associated with the extension of the Earth's crust and its rise under the influence of tangential stresses. The latter can be explained by the subhorizontal penetration of the high-speed layer of the transition zone of the upper mantle from the Black Sea into the low-speed layer of the transition zone of the upper mantle of Sarmatia. An analysis of the distribution of velocities over horizontal sections of the mantle beneath the DDD and its surroundings makes it possible to single out the layering of the upper mantle and its transition zone. Stratification is determined by characteristic velocity regions for a given depth, limited both by zero velocity isolines and by thickening of isolines. A total of 5 areas are allocated: at depths of 50—250 km, 300—400 km, 450—550 km, 600—650 km, 650—800 km. At depths of 300—400 km, the region combines the Kursk-Belgorod block of the Kursk megablock of the Voronezh crystalline massif, the Chernigov and Lokhvitsky segments of the DDV, the Ingul and Pridneprovsky megablocks of the Ukrainian Shield, and is supposedly part of the Sarmatian Shield associated with the mantle beneath the Volga-Uralia-Ural-Ural macrocontinent.The propagation directions of velocity structures associated with the mantle under the DDW are distinguished: south—northeast, south—northwest, north—south, east—west. More generally, it is northeast—southwest, south—north, east—west.