Home – Home – Jornals – Russian Geology and Geophysics 2024 number 10

The paper presents data from a comprehensive study of granitoids identified in the Mayorka intrusion that is located in the western part of the Altai Mountains. It is shown that the massif is composed of rocks of four intrusive phases, the age of these rocks ranges from 391 to 372 Ma, and the intrusion of the main volume of granitoids dates back to a relatively short interval of 386-384 Ma. The massif contains rocks of two geochemical types. The first type is differentiated calc-alkaline granite-leucogranites with near-clark contents of high-field-strength elements and rare earth elements: ɛ_Nd( T ) = + 4.3…+ 4.5 and δ¹⁸O V-SMOW = +10.7…+11.2 ‰. The second is alkaline and moderately alkaline A-type alyaskites, strongly enriched in high-field-strength elements and rare earth elements, having ɛ_Nd( T ) + 5.3 and δ¹⁸O V-SMOW = +11.6 ‰. Granitoids of the first group are of crustal source, while the rocks of the second group contain a significant portion of mantle material. The near-simultaneous introduction of these melts to the level of formation of the intrusion causes their interaction and the formation of hybrid magmas. Low crystallization temperatures of granitoids (<700 °C) and the presence of syngenetic melt and fluid inclusions in most rock varieties indicate a high fluid saturation of the melts. The abundance of leucogranites, whose geochemical characteristics cannot be explained from the standpoint of shallow differentiation of primary magmas, indicates the leading role of fluid-magmatic interaction processes in the formation of high-silica magmas.

We summarize the results of geological, geochronological and petrochemical studies of the intrusive complexes of West Sayan, and on their basis analyze the scales, formation sequence, petrochemical characteristics and geodynamic environments of the formation of granitoid and gabbroid complexes. Geochronological data indicate that the formation of intrusive complexes (granitoids and gabbroids) of West Sayan ranged within 580-370 Ma at several age levels and in various geodynamic environments: island-arc - 580-570, 550-520 Ma, accretion-collision - 505-450 Ma, transform-shear of continental margins - 440-430 Ma, and active continental margin - 425-370 Ma. According to petrochemical characteristics, we distinguish the rocks of tholeiitic, calc-alkali and subalkaline series among the studied granitoid complexes. The study of xenogenic zircons from granitoid and gabbroid complexes indicate the age range of 650-440 Ma. Several age clusters are distinguished (~ 645, ~ 570, 555-520, 505-475, 455-440 Ma); this indicates heterogeneous composition of the West Sayan crust and participation of the Late Riphean, Vendian - Early Cambrian and Ordovician crust sources in granite formation.

We present results of studies of inclusions in secondary sulfates (antlerite and a mixture of copiapite and coquimbite) and arsenates (erythrite and picropharmacolite) formed on the surface of technogenic bodies, such as stored waste from the enrichment of sulfide (Belovo and Ursk waste heaps) and arsenide (disposal maps of the Tuvakobalt plant) ores. A wide range of components were identified in the gas-liquid inclusions, the main ones being water and carbon dioxide. Hydrocarbons, oxygen-containing organic compounds, and nitrogen- and sulfur-containing gases were found in smaller but measurable amounts. Arsine H₃As was also detected in inclusions in picropharmacolite (calcium and magnesium arsenate-arsenite). The gas-liquid inclusions in secondary minerals reflect the composition of the interporous space in the waste body, filled with particular atmospheric gases entering the body in free form and with seasonal precipitation. The combination of in situ generated and penetrating gases determines the diversity of inorganic and biotic interactions in technogenic bodies. The presence of hydrocarbons and oxygen-containing organic compounds is, most likely, associated with bacterial transformations of organic matter (residual vegetation, wood, microalgae, and fungi). At the same time, carbon disulfide and sulfur dioxide are indicators of active inorganic reactions of decomposition of the sulfide matrix.

The main types of reservoir rocks have been identified within the Bazhenov-Abalak complex. To assess the geological resources of hydrocarbons, it is proposed to formally divide the entire set of lithological rock types comprising the Bazhenov-Abalak complex into two main varieties: fluid seals and reservoirs. We argue that it is possibile to distinguish between potentially productive and productive rocks, represented by siliceous and carbonate varieties, according to logging data. A possible mechanism for the formation of reservoir rocks within the Bazhenov-Abalak complex as a result of the tectonic-hydrothermal impact on these deposits has been reconstructed. An original methodology for identifying perspective zones of various categories of hydrocarbon accumulation in the Bazhenov-Abalak complex through integrating seismic data and tectonophysical modeling carried out on their basis has been proposed. For example, an assessment of the predicted geological resources of hydrocarbons contained in the Bazhenov-Abalak complex within the limits of 3D seismic exploration of the Yem-Yegovskaya area has been carried out. The necessity of assessing the prospects for oil content and calculating the predicted geological resources of hydrocarbons in the whole Bazhenov-Abalak complex, and not only in the Bazhenov Formation, is substantiated, based on a single mechanism of formation of reservoir rocks of tectonic-hydrothermal origin in them.

We have compiled maps of areal isotope composition changes and constructed graphs of gas HC distribution depending on the stratigraphic age of the host rocks and graphs of isotope composition changes depending on the depth of sampling to study the hydrocarbon potential of the deep-seated oil and gas pools of the South Caspian Basin. The genesis of gas was studied using the techniques elaborated by M. Schoell and A. James. Two stages of hydrocarbon formation have been established by study of various kinds of gas manifestation. The first stage (Miocene-Eocene) began in the deposits underlying the Productive Series and continued up to the deposits of the latter. This stage was characterized by a frequent change in the directions of both downward and upward movements of gases. The second stage of hydrocarbon formation (Anthropogene-Pliocene) began in the deposits of the Productive Series and was characterized by a change in the regional geodynamic setting. Avalanche sedimentation and the predominance of downward movements over upward ones favored the accumulation of thick sediments at the time when the Productive Series formed. The sedimentation and tectonic processes (downwarping) in the deep-water zone of the basin led to harsh thermobaric conditions in the sedimentary strata. A detailed analysis of the results of gas survey in the deep-water zone of the South Caspian Basin has shown gas generation with a predominance of two components, methane and ethane. Study of the trends of temporal and areal hydrocarbon migration and of the areas of oil and gas generation makes it possible to reveal structures with evidence for large and giant hydrocarbon reserves. We have established that gas hydrocarbons in the bottom and upper-section sediments of the southern Caspian Sea are intimately related to the sources of hydrocarbons, their migration, and other processes running in the deep-seated sediments and in the upper section.

The three-dimensional dynamic problem solution of the theory of elasticity as it applies to modeling of all types of seismic waves propagating in real geological media is considered. The elements of the 3D forward modeling algorithm based on the spectral element method (SEM) for the numerical solution of the problems posed are presented. The SEM’s main characteristics (high order spatial discretization, explicit time integration scheme) and its advantages are compared with the classical finite element method (FEM). Distinctive features of massively parallel implementation of this algorithm on NVidia’s GPU using CUDA (Compute Unified Device Architecture) are considered. The efficiency of parallelization on hybrid systems at different orders of SEM and parameters of the numerical scheme of time integration is analyzed. Results of solving a three-dimensional problem of modeling seismic wave propagation in a heterogeneous geological medium with faults and strongly varying (vertically and horizontally) properties of the investigated layers are presented. A highly detailed digital geological model constructed for one of the petroleum fields in the Arctic region using Petrel, the world’s most popular geological modeling tool, is used as input datasets. The problem was solved on a mesh of hexahedral elements in 3D to perform efficient SEM calculations in the CAE Fidesys software developed earlier with the authors participation for engineering simulations (strength analysis, etc.). The derivation of the model was based on the typical seismogeological conditions of Western Siberia so that the modeling allows investigating look-ahead capabilities of numerous seismic exploration methods for an in-depth study of major oil-and-gas-bearing complexes in this region. The prospects of model implementation for other candidate regions with different geological structure are equally promising. Outputs of the full-waveform seismic modeling is stored in the standard SEG-Y format currently widely used worldwide in industry for seismic data processing. The obtained synthetic seismograms and seismic wave fields are analyzed. The practical significance of the conducted research whose results can be utilized in the future for solving a wide range of applied tasks for regions with different geological conditions is deduced.

This work is set out to summarize, analyze and revisit results of the geothermal studies carried out in Northeast Russia. A catalog of measured heat flow values has been compiled, and on its basis a map of the region’s heat flow distribution has been constructed. Geodynamic activity of the tectonic structures in Northeast Russia, their thermal regime in which the heat flow is a critical indicator, is largely determined by the interaction between the Eurasian and North American lithospheric plates and smaller-order plates located in the northeastern part of the Asian continent. The areas of interaction between the Eurasian and North American lithospheric plates are marked by the Arctic-Asian seismic belt, which is characterized by intense orogenesis, modern volcanism, active seismicity, diverse geothermal regimes, and large heterogeneity of measured heat flow values. On the Chukotka Peninsula, the helium isotope method was used to estimate heat flow values. It is proposed to consider the class of geodynamic activity of tectonic structures as one of the factors of the geothermal regime.

For the territory of the Middle Urals segment, a high-resolution grid density model of the upper part of the lithosphere was constructed (grid step is 500 m) to the depth of 80 km - the first regional level of isostatic compensation. The spatial framework of density sections serves as the basis for a three-dimensional (3D) interpolated density model - an initial approximation model. The corrections to the density model of the initial approximation are found from the solution of the linear inverse gravimetry problem of practically meaningful correctness sets of density equivalents. The fairly thin horizontal layers of the grid density model are selected as such sets. The method and technology to calculate 3D density distribution with reference to 2D data along reference seismic sections are embedded in the methodology for quantitative interpretation of potential fields with the construction of 3D geophysical models. The relief of the internal boundary surfaces of the upper, middle and lower crust is compared to the structural scheme of tectonic zoning along the surface of the basement. To construct tectonic schemes, lithostatic pressure anomalies are also used; they are calculated from a general integral characteristic - the mass of density columns from the earth’s surface to a given depth. Anomalies of lithostatic pressure for each layer of a 3D grid density model are proportional to excessive density within the layer, so that a density model is easily converted into a lithostatic model. 3D anomalies of lithostatic pressure clearly configure the block structure of the earth’s crust at different depth sections. In the projection at the surface of the middle and lower crust, the contours of lithostatic anomalies correspond to the tectonic zoning scheme of the basement, built based on potential fields. A comparison of ‘block diagrams’ of density and lithostatic models is used to identify structural elements of different order of deep tectonic zoning at different depth sections.

This research focuses on analyzing landslides triggered by a moderate earthquake ( M_w = 4.9) in the northeastern region of the Mila province, which resulted in significant damage and economic losses in the El Kherba district and Grarem Gouga city. Through an extensive field-based investigation, a comprehensive inventory of landslides has been compiled. To assess the susceptibility to landslides triggered by seismic activity, a GIS-based fuzzy logic model was employed. The model incorporates various input factors, such as lithology, slope angle, normalized difference vegetation index (NDVI), distance from rivers and roads, precipitation, and seismic hazard, which is shown on a map. The study compares the performance of different fuzzy operators and gamma values and determines that using fuzzy gamma operators with a gamma value of 0.8 yields a satisfactory consistency with the distribution of landslides. Moreover, incorporating the map of seismic hazard as a causative factor enhances the accuracy of landslide susceptibility mapping. This study underscores the utility of the fuzzy logic model in disaster management and the planning of development activities.