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No 3 (2023)

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Structure Formation of the Southeast Indian Ridge at the Early Stages of Development: Physical Modeling

Agranov G.D., Dubinin E.P., Grokholsky A.L., Leichenkov G.L.


The authors of the article studied the features of the structure formation of the earth’s crust in the early period of the formation of the Southeast Indian Ridge, associated with the separation of Australia from Antarctica and the advancement of the rift zone to the west within the ancient oceanic lithosphere towards the large magmatic province of Kerguelen, formed by the activity of the plume of the same name. The separation of Australia and Antarctica covered a long period of continental rifting (~160‒80 Ma), which then turned into ultra-slow spreading (~80‒45 Ma), then into slow spreading (~45‒40 Ma) and then into stationary spreading at average rates (after 40 Ma). The advance of the rift zone towards the ancient oceanic lithosphere gave way to the accretion of young oceanic crust on the emerging Southeast Indian spreading ridge. The early stages of development of the young spreading ridge are captured in the modern structural plan of the study region. The advance of the rift zone from the continent into the boundaries of the ancient oceanic lithosphere led to the formation of the Naturalist Plateau and the Bruce Bank near the Antarctic margin. The split of the ancient oceanic lithosphere and the formation of a young crust on the Southeast Indian Ridge led to the formation of conjugated Diamantina and Labuan suture zones, fixing the position of the initial rift split. The transition from ultraslow spreading at the initial stage of oceanic crust formation to stationary spreading with medium velocities is clearly recorded in the change in the irregularity of the accretionary relief. The Southeast Indian Spreading Range westward collided with a large igneous province during the formation of the Kerguelen Plateau and separated the Broken Range from the plateau. The authors carried out physical modeling of the conditions for the occurrence of rifting and spreading processes, as well as structure formation in the region of the Southeast Indian Ridge.

Geotektonika. 2023;(3):3-16
pages 3-16 views

Structural Styles of Thrust Zones of the Urals and Pay-Khoi Foredeep

Sobornov K.O.


The article presents an interpretation of geophysical data characterizing the structure of the frontal fold and thrust zones of the Urals and Pay-Khoi, which show the diversity of structural styles of deformations in the study region. The following structural styles of deformations are considered: classical-style thrust zones, which are in-sequence thin-skinned imbrication systems (i); areas of distribution of wedge-shaped allochthons, composed of duplex tectonic plates that are not reflected in the sub-surface layers (ii); inversion zones where faults associated with Ural rifting are transformed into thrust faults (iii); areas whose structure is determined by the deformation of salt diapirs and extrusion of salt (iv); zone, tectonic thickening of the Precambrian complexes overlain by the Paleozoic cover (v). Interpretation of historical and new data on the structure of fold belts makes it possible to significantly update understanding of the structure and development of areas such as zones of wedge-shaped thrusts, areas of development of squeezed salt diapirs, and areas where reactivation and tectonic thickening of Precambrian complexes occurred due to the reactivation of pre-existing faults. New seismic data provided constraints on the magnitude of horizontal displacements in the thrust zones as well as timing of shortening. For the first time they have revealed the development of arrays of small-scale protothrusts.

Geotektonika. 2023;(3):17-40
pages 17-40 views

Geological Structure of Deep-Submerged Complexes of Sedimentary Basins: Hydrogeological Anomalies and Oil and Gas Potential as a Result of Implementation of Deep-Seated Fluids (on Example of the South Mangyshlak Fields)

Popkov V.I., Larichev V.V., Popkov I.V.


The authors of the article substantiate the induced nature of hydrogeological anomalies in deep-submrged complexes of sedimentary basins. As a result of significant catagenetic transformations, the rocks of the lower hydrogeological floor have practically lost their primary capacitance-filtration properties. The water saturation of the rock matrix, the focal nature of the development of secondary reservoirs against the background of extremely low permeability of the surrounding strata makes it impossible to develop elision flows. This causes the high sensitivity of the lower floor to various compression processes, including those caused by the intrusion of the deep high-energy fluid flows. The injection of these fluid flows into low-permeability strata leads to the formation of centers of desalinated waters of various hydrochemical types, from hydrocarbonate-sodium to calcium chloride, and also to the formation of hydrodynamic anomalies. When moving away from the intrusion channels, the hydrodynamic and hydrochemical parameters gradually level off, approaching the background value. It is shown that when fluids are difficult to move upward, hydraulic fracturing occurs in the layers into which the oil-water mixture enters under high pressure. The injection of fluids into the formation is accompanied by the decompression of low-permeability strata, the formation of additional fractures, and the formation of secondary voids of metasomatic origin. As a result, secondary reservoirs of complex morphology are formed, filled with hydrocarbons. The coincidence in terms of hydrogeochemical and hydrodynamic anomalies, areas of secondary reservoirs with distinct traces of metasomatosis and associated accumulations of oil and gas indicate their genetic relationship. The oil and gas reservoirs and their accompanying hydrogeological anomalies are considered on the example of the fields of the South-Mangyshlak oil and gas region, which is part of the North Caucasian-Mangyshlak oil and gas province.

Geotektonika. 2023;(3):41-66
pages 41-66 views

Seismotectonic Analysis and Development of the Mathematical Model of the Stress-Strain State of the Earth’s Crust in the Zone of Collision of the Western Tien Shan with the Pamir Arc

Sadykov Y.M., Atabekov I.U., Ibragimov R.S.


The seismotectonics of the Western Tien Shan is determined by collisional processes in the zone of interaction between the Southern Tien Shan and the Pamir arc. This process contributes to maintaining the high seismic potential of the region, as evidenced by the destructive earthquakes that have taken place here from ancient times to the present and their traces - seismic dislocations. Strong earthquakes are genetically associated with areas of intense movements in recent and modern times, with zones of active faults. An improved map of the active faults of the Western Tien Shan has been constructed and, on its basis, a mathematical model of the stress-strain state has been constructed using the Stokes equations. At the same time, the dynamic influence zones of the South Fergana and North Fergana faults are additionally included in the model. At the same time, a significant correction was obtained in the distribution of stresses in the earth’s crust of the region. The velocity fields of modern movements of the Western Tien Shan corresponding to GPS data are analyzed. The displacement velocity vectors are grouped in the direction into several zones. The nodes of intersection or articulation of movements of different directions are assigned to the most tectonically stressed areas. The most active seismic zones are identified on the basis of these nodes and the resulting stresses. They are compared to similar areas with a high concentration of strong earthquakes.

Geotektonika. 2023;(3):67-77
pages 67-77 views

Seismotectonic Consequences of the Strong Earthquake Mauli (February 27, 2010, = 8.8) in Chile: Digital Modeling of the Crust Stress-State of the Western Margin of the South American Plate

Morozov V.N., Manevich A.I.


This article presents seismotectonic consequences of the strong Mauli earthquake in Chile, which occurred on the February 27, 2010, Mw = 8.8. The consequences are considered as a manifestation of a large-scale fragment of the general seismotectonic process on the western edge of the South American plate (Chilean sector). Our study shows that manifestations of postseismic processes of the Maule earthquake cover a much larger area compared to the epicentral zone of the aftershocks. Based on the comparison of the results of numerical modeling of the stress-strain state before and after the earthquake, seismological, geodetic, and satellite data, an alternative model of the development of the seismotectonic process in the Chilean sector of the South American plate was proposed. The stress-strain modeling was performed by the finite element method. The source of the Mauli earthquake, at a depth of 33 km, falls into the region of relatively high values of compression stresses and positive maximum shear stresses. It was shown, that other strong earthquakes of the Chilean sector in the interval of depths from 20 to 50 km are caused by high concentration of tectonic stresses in the region of transition from oceanic to continental lithosphere. Within the framework of the proposed model of the seismotectonic process, ruptures weaken the contact between the oceanic and continental lithosphere after strong earthquakes. Abrupt sinking of the continental lithosphere into the mantle causes an increase in viscous melt pressure, promotes penetration into mega-cracks, and rises to the surface, causing subsequent volcanic eruptions. It is shown that the results obtained in comparison with the coseismic consequences of earthquakes do not contradict these results of numerical modeling and give new insights into the structure of the lithosphere in the continent‒ocean transition zone and the development of the seismotectonic process.

Geotektonika. 2023;(3):78-93
pages 78-93 views
pages 94-96 views

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