Geotektonika
ISSN (print): 0016-853Х
Founder: Russian Academy of Sciences
Editor-in-Chief: Kirill Evgenyevich Degtyarev, Academician of the Russian Academy of Sciences
Frequency / Access: 6 issues per year / Subscription
Included in: White List (1st level), Higher Attestation Commission List, RISC
Media registration certificate: No. 0110282 dated 02/08/1993
Ағымдағы шығарылым
Ашық рұқсат
Рұқсат берілді
Тек жазылушылар үшін
№ 2 (2024)
Articles
Active faults of the northern Central Mongolia, their correlation with neotectonics and deep structure of the region
Аннотация
Active tectonics of the northern Central Mongolia is studied between two largest W–E-trending left lateral fault zones – the Khangai Fault and the Tunka-Mondy zone. These strike-slip zones are parts of a single ensemble of active faults in the Mongol-Baikal region, formed under conditions of the maximum northeastern compression and the maximum northwestern extension. Between them, the ENE-trending Erzin-Agardag and Tsetserleg faults with dominant left lateral component of movements extend. A raw of the N-trending graben-shaped basins (Busiyngol, Darkhat, and Hubhugul) are situated between the eastern end of the Erzin-Agardag strike-slip fault and the western part of the Tunka-Mondy strike-slip zone. The basins form a zone of left lateral deformation, which is kinematically similar with the strike-slip faults continuing it. In contrast to the largest boundary strike-slip faults, this structural paragenesis was formed under conditions of N–S-trending relative compression and W–E-trending extension. A change in the orientation of the axes of the principal normal stress may be caused by the rotation of the block between the boundary faults. The area of graben-shaped basins is located above the uplift of the roof of a vast volume of low-velocity mantle, which we identify as the Khangai plume. Above this rise, the lithospheric mantle is reduced, and the remaining part of the lithosphere is heated and softened. The large active strike-slip faults are located above areas of lowering of the low-velocity mantle roof. Our trenching of the active faults showed that strong earthquakes repeated in the area of graben-shaped basins more often than in the large strike-slip zones, but were characterized by lower magnitudes.
3–33
Theoretical and experimental modeling of geodynamiс processes in uplift slopes
Аннотация
The flow structure created in a viscous medium at a constant inclination angle of the free surface of the uplift slope is analyzed. The velocity field in a high-viscosity uplift slope is determined under conditions of a horizontal pressure gradient. This pressure gradient occurs when the slope height decreases with distance from the main ridge. With a constant dynamic viscosity of the uplift slope, the flow velocity in it decreases with distance from the axis of the main ridge. In this case, the uplift slope is in conditions of compressive stresses, the consequence of which are thrusts and compression folds. Tensile stresses in the uplift slope exist with an increase in the flow velocity in the layer with distance from the main ridge axis. The flow velocity increases with decreasing viscosity of the layer with distance from the main ridge. The viscosity distribution on the base of the uplift slope at a distance from the axis of the main ridge is determined using the tension condition in the uplift slope. Expressions are presented for the forces causing the formation of a disruption between the blocks of the uplift slope. The magnitudes of these forces are estimated. A relation representing the condition for the formation of a disruption between the blocks is obtained. The formation of disruptions is governed by the change in viscosity along the uplift slope and the change in the flow velocity in it. When the disruption between the uplift slope is formed, free vertical boundaries of the blocks appear. The motion of a highly viscous liquid during the formation of a free vertical boundary of the block has been studied experimentally when the liquid flows out from a rectangular vessel. The experiments have revealed two outflow regimes: (i) the regime of constant thickness of the liquid layer; (ii) the regime of decreasing layer thickness. On the basis of experimental modeling the time of the first period after the formation of the slope rupture and the formation of the free volume between the blocks is estimated. During this period the height of the layer (slope) is practically constant and the layer length increases. The process of filling the free volume between the blocks with a high-viscosity slope material is considered. As the modeling shows, the filling rate of the free volume between the diverging blocks of the uplift slope is much higher than the formation rate of the free volume between these blocks. The parameters of the uplift slope blocks are determined. Among these parameters are block viscosity, slope height, flow velocity and forces acting on the blocks. The time-varying structure of the surface of the uplift slope is presented. There is a qualitative correspondence between the modeling results and the profile of the uplift slope for the north-western Caucasus.
34–53
The geological structure of the Gakkel Ridge: in the light of new geological and geophysical data
Аннотация
In 2011‒2020 the significant amount of seismic lines was carried out in the Eurasian Basin of the Arctic Ocean, which made it possible to study the structure of the junction zones of the Gakkel Ridge with the Nansen and Amundsen basins on a number of profiles. During 2019‒2020 15 sections of the Gakkel Ridge and its rift valley were studied using a sub-bottom profiler and seismo-acoustic profiling. New data on the relief of the basement, as well as the use of databases of bathymetry, gravity and magnetic anomalies updated at VNIIOkeangeologia, made it possible to calculate the magnetization of the rocks of the Gakkel Ridge along a number of profiles crossing the ridge, and to perform the model calculations of the Earth’s crust structure using a complex of geological and geophysical data in the area of the southeastern termination of the ridge. The Gakkel Ridge is a structure, the isolation of which refers to the time interval of Early Oligocene (34 Ma)–Early Miocene (23 Ma), in the process of radical restructuring of the spreading kinematics in the already existing ocean basins in the regions of the North Atlantic and the Arctic. The values of the calculated magnetization of the magnetic layer of the Earth’s crust show that this layer is partly composed of oceanic basalts, but mainly of deep-originated rocks, gabbro and peridotites, brought to the surface during detachment accompanying spreading. The Laptev Sea continuation of the rift valley of the Gakkel Ridge, to the south of the caldera, passes above many kilometers of sediments, at the base of which sedimentary rocks of Cretaceous and Late Jurassic age occur.
54–71
Tectonic basis for oil and gas potential in the North Kara prospective area (Western Arctic, Russia)
Аннотация
The Arctic shelf of Russia, and, in particular, the shelf of the Kara Sea, is one of the unique regions of the world with enormous hydrocarbon potential, however, due to the harsh weather conditions, it has been studied unevenly. The lack of deep and parametric drilling data in the northern part of the Kara Sea leads to numerous uncertainties in models of the geological structure of the region and, as a consequence, to uncertainties in assessments of the resource potential of this Arctic region. A large volume of 2D CDP seismic exploration was carried out in the northern part of the Kara Sea. The results of these works made it possible to clarify the geological structure of the Kara Plate, substantiate the boundaries of the North Kara independent promising region and promising areas within it, and assess hydrocarbon resources.
72–83
Geological characteristics оf subpermafrost gas hydrate reservoir оn the Taimyr shelf of the Kara Sea (Eastern Arctic, Russia)
Аннотация
The conditions for the formation of gas hydrates associated to subsea permafrost in the Kara Sea are predicted based on numerical modeling. The forecast of the distribution of the relic submarine permafrost and related methane hydrate stability zone is given on the basis of solving the equation of thermal conductivity. According to modeling data, an extensive thermobaric relict submarine permafrost zone is predicted within the Kara Sea shelf. The greatest thickness (up to 600 m) of the permafrost is confined to the Taimyr shelf. Based on the results of the analysis of our model, drilling seismic data, the southwestern shelf of the Kara Sea is characterized by insular or sporadic permafrost. In the northeastern part, the nature of permafrost is also discontinuous, despite the greater thickness of the frozen strata. For the first time, accumulations of cryogenic gas hydrates on the Taimyr shelf have been characterized. The new drilling data obtained, seismic data reinterpretaion and numerical modeling have shown that the gas hydrate reservoir is confined to unconformably occurring Silurian‒Devonian and underlying Triassic-Jurassic strata. The thickness of the gas hydrate reservoir varies from 800 to 1100 m. Based on the interpretation of CDP data and their comparison with model calculations, frozen deposits and sub-permafrost traps of stratigraphic, anticline and anticline-stratigraphic types were identified for the first time. These pioneering studies allowed to characterize the thickness and morphology of the gas hydrate reservoir, giving a preliminary seismostratigraphic reference, and to identify the potentially gas-hydrate bearing structures. Due to favorable thermobaric and permafrost-geothermal conditions, most of the identified traps may turn out to be sub-permafrost accumulations of gas hydrates. In total, at least five potential accumulations of gas hydrates were discovered, confined to structural depressions ‒ Uedineniya Trough and its side included Egiazarov Step and North Mikhailovskaya Depression.
84–108