Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

Using the example of active faults in the high mountainous part of the Gorny Altai (South Chuya and Kubadu fault zones) and the Lena River delta (Primorsky Fault Zone), active fault zones in the conditions of permafrost development were studied using the electrotomography technique. The method was shown to be effective in identifying active fault zones to depths up to the first hundred metres in permafrost conditions. However, the presence of icy rock with a resistivity greater than 100 kOhm·m limits its application due to the shielding effect of the insulating layer. The main criterion for identifying active faults in geoelectrical sections are subvertical zones of reduced resistivity against a background of high resistivity permafrost layers. This concerns both relatively young seismic ruptures formed during the Chuya earthquake (Ms=7.3) 27.09.2003 in the South Chuya Fault Zone and more aged Holocene fault scarps in the zones of the Kubadru and Primorskiy faults. At the same time, resistivity values in the zones of active faults and seismic ruptures are too high to assume their saturation with free water. The decrease in resistivity in such zones relative to the host permafrost frame may be due to: 1) increased rocks and sediments fracturing; 2) occurrence of thinly fractured material in the core fault zones, including in cracks, where physically bound non-freezing water is concentrated; 3) residual thermal anomalies in the case of modern activations, so that negative temperatures have already been restored, but the process of frozen strata degradation is not fully completed yet; 4) saturation of the geological section with sandy-silty material as a result of the development of liquefaction and fluidization processes during earthquakes. The revealed regularities can be used not only to confirm the zones of morphologically distinctive segments of active faults, but also to search for their buried segments in the areas of permafrost development typical for seismically active high mountain and Arctic regions of Russia and worldwide.

Three mid-oceanic ridges meet in the area of the Bouvet triple junction the Mid-Atlantic, Southwest Indian and American-Antarctic one. At the same time, the triple junction area is characterized by manifestations of magmatism of the Bouvet hotspot. Using available laboratory modeling data, a scheme is presented for the conduit of a thermochemical mantle plume melting from the core-mantle boundary and breaking through to the surface. Using morphobatimetric data for the area of the Bouvet volcanic island, a mass flow rate of magmatic melt for the plume of the Bouvet hotspot was found. Taking into account the melt flow rate, the thermal power of the Bouvet plume source is N_B = (1.7–2.0) · 10¹⁰ W, and the plume conduit diameter is 9 to16 km. Based on the consideration of the geodynamic regime, the possible evolution of the Bouvet plume is presented. The influence of the geodynamic system of asthenospheric convective flows on the structure of the ocean floor in the Bouvet area is shown. The Bouvet Island was formed under the influence of mantle plume. The Bouvet plume is located in the area of the ascending flow of the asthenospheric rolls and contributes to the roll flow intensification. Transform faults in the Bouvet area were formed under the influence of descending flows of asthenospheric rolls. The width of the trough and the depth of the Bouvet transform fault are determined based on the analysis of the flow structure and heat transfer in the asthenosphere in the Bouvet area. The contribution of the Bouvet plume to the asthenospheric convection roll intensification is also taken into account in our calculations. The conducted geochemical and thermobarogeochemical studies indicate the decisive role of fluid components in magmatic systems of the Bouvet hotspot, which are characterized by enrichment with volatiles (H₂, H₂O, CO₂), alkali (primarily potassium) and lithophilic rare and rare earth elements (La, Ce, Th, Nb, Rb). Taking into account the seismotomographic results, the features of the mantle structure in the triple junction are considered. A high-velocity anomaly is detected along the axial zone of the Bouvet transform fault. The roots of this upper-mantle anomaly can be traced to a depth of 250 km. A low-velocity anomaly has been detected under Bouvet Island. This anomaly can be traced to depths of about 500 km.

The paper deals with the age, composition and features of the genesis of granitoids of the Soktuy massif – the petrotype of the Kukulbey complex of Mesozoic rare-metal granites of Transbaikalia. The Soktuy massif is heterogeneous. Several petrographic varieties are distinguished: monzo- granite-leucogranites and microleucogranites of the main intrusive phase, alaskites, alkali-feldspar granite porphyries, granodiorites and quartz syenites of the additional intrusion phase According to the obtained U-Pb-geochronological data, the age of all varieties is indistinguishable taking into account the analytical error and corresponds to the Early Cretaceous. Granitoids differ in a variety of geochemical characteristics: monzo- granite-leucogranites of the main intrusive phase belong to the rare-metal-plumasite type, rocks of the phase of additional intrusions show signs of A-type granitoids. The geochemical and isotopic characteristics of the rocks indicate the participation in their formation of both substrates of the continental crust and deep magmas of mantle genesis. The volatile content in micas and the peculiarities of the composition of inclusions indicate that the formation of magmas occurred with the participation of two types of fluids: chloride and reduced (probably mantle) and more oxidized fluoride (presumably having a lower-crust nature). All melts were generated at depths of no more than 30 km, and the depth of formation of the massif did not exceed 8 km. Based on the obtained data set, a model for the formation of rocks of the massif is proposed.

The junction zones of mountain ranges with sedimentary basins are concentrators of seismogenic faults that develop in settings of regional compression and transpression. The development of two opposing systems of reverse faults and thrusts forms positive (forbergs, “pop-up” structures, fault and tectonic scarps, fault related fold) and negative morphostructures (“pop-down” structures) at the edges of sedimentary basins. As a result, the edges of the basins are involved in uplift. This leads to a gradual growth and expansion of the mountain ranges and a reduction in the areas of intramountain basins, i.e. the reduction mechanism of the upper part of the earth's crust is realized. However, the mechanisms of the emergence of conjugate fault systems are not fully understood. The mechanisms of such deformations in the upper part of the earth's crust were investigated under lateral compression of the rock mass using two-dimensional numerical modeling. The elastic-plastic approximation of the Drucker-Prager-Nikolaevsky model with a non-associated flow law was used. In all models, regardless of the number of layers, reverse faults and thrusts with direct and reverse dips relative to the direction of horizontal compression were formed. As a result, positive and negative structures were formed in the relief of the models, which are analogs of the corresponding natural morphostructures. The obtained results showed that the development and configuration of localized shear bands corresponding to reverse faults and thrusts are influenced by elastic-strength properties, basal friction, and boundary conditions at the lateral boundaries of the model. It has been established that in a multilayer medium a multilayer system of localized shear bands can form because of one stage of deformations that have different slopes and are limited only to a specific layer. Special attention should be paid to models in which interlayer slippage develops. It is caused by different rates of layer displacement relative to each other due to differences in the elastic-strength properties of rocks, which leads to the development of reverse thrusts in the upper part of the section that are not associated with the base of the model. Typically, such thrusts develop in the upper part of the section. Heterogeneities in the base of the models, regardless of strength properties, can affect the spatial localization of localized shear bands that arise at their boundaries. The results of numerical modeling allowed us to better understand the relationship between the mechanical properties of rocks and sediments with the features of the development of reverse-thrust structures.

The study of the spatial distribution of individual groups of marine invertebrates in the geological past and the analysis of the dynamics of their geographical differentiation over time are of great importance both for identifying patters of their evolution and for understanding the history of marine basins. In this work, taking into account modern data on paleontology and biostratigraphy of the Boreal Triassic, the taxonomic composition and distribution of Ladinian ammonoids in different regions of the Boreal Realm are specified. Zonal correlation on ammonoids of the Ladinian deposits of northeastern Asia, British Columbia, Arctic Canada, northern Greenland, Svalbard and Franz Josef Land is carried out, a chronological basis for comparative analysis of coeval ammonoid faunas is obtained. As a result of qualitative and quantitative comparative analysis of ammonoid complexes for different phases of the Ladinian Age, it is established that northeastern Asia was constantly part of the Siberian Province of the Boreal Realm. The separation of the Canadian province of the Boreal Realm occurred at the end of the constantis phase due to the penetration of trachyceratids (genus Protrachyceras) into the paleobasins of Arctic Canada, later, starting from the maclearni phase, its area increased due to the migration of Tethyan forms into the paleobasins of Svalbard. The migrations of trachyceratids, gymnitids and lobitids into boreal paleobasins from the Tethys, as well as boreal tsvetkovitids and nathorstitids into ecotone and Tethyan paleowaters of British Columbia were caused not only by circumpolar currents, but were probably associated with the lifestyle of ammonoids and their habitation in a greater or lesser range of depths of marine basins.

Experimental studies on modelling of diamond resorption processes during mantle oxidative metasomatosis in solid-phase matrix in the presence of intergranular fluid have been carried out. The reaction between diamond and periclase with formation of magnesite was realised, which can be considered as a model variant of such reactions as EMOD (enstatite-magnesite/olivine-diamond) or DCDD (dolomite-coesite/diopside-diamond). The studies were performed at a pressure of 6.3 GPa in the temperature range 1100-1400 °C under redox conditions corresponding to the WM (wustite/magnesite) buffer. It was found that the reaction between diamond and periclase to form magnesite occurs only in the presence of 0.5-0.8 wt.% water at temperatures above 1200 °C. The morphology of diamond crystals partially dissolved by intergranular H₂O-fluid at fO₂ at WM buffer level is typomorphic for diamond dissolution/resorption in water-containing carbonate and carbonate-silicate melts. The main microrelief elements of diamond dissolution shapes are inversely orientated triangular etch pits on relict octahedral faces, shield-shaped or ditrigonal dissolution layers, and drop-shaped hills. The obtained resorption rates at these P-T-fO₂ parameters indicate that the absence of diamond or poor diamondiferousness of potentially diamondiferous kimberlite pipes may be due to oxidative metasomatosis in the mantle regions of pipe formation.

mourite, uranyl molybdate, crystal structure, infrared spectroscopy, chemistryA synthetic analog of mourite (SM), (UO₂)Mo₅O₁₄(OH)₄(H₂O)₂, has been hydrothermally synthesized at 220 ºС and characterized using single-crystal X-ray diffraction, single-crystal and powder X-ray diffraction studies at non-ambient temperatures, X-ray photoelectron spectroscopy, infrared spectroscopy, thermal, and chemical analyses. SM is monoclinic, P2/c, a = 9.9063(6), b = 7.1756(4), c = 12.2105(7) Å, β = 102.496(6)°, V = 847.41(9) ų; the crystal structure has been refined to R₁ = 0.043. The chemical composition of the SM is (the Mo₂O₅:MoO₃ ratio obtained from X-ray photoelectron spectroscopy, H₂O by stoichiometry; wt.%): Mo₂O₅ = 4.61, MoO₃ = 61.06, UO₃ = 26.95, H₂O = 6.76, total 99.38. The empirical formula calculated on the basis of 22 oxygen atoms per formula unit with Mo^V+Mo^VI = 5 is (U^VI_1.03O₂)[(Mo^VI_4.63Mo^V_0.37)_Σ5.00O_13.81(OH)_0.19](OH)₄(H₂O)₂. The crystal structure of SM contains UO₈, Mo1O₆, Mo2O₅(H₂O), and Mo3O₄(OH)₂ polyhedra that share vertices and edges to form layers linked by hydrogen bonds only. SM is stable up to 250±10 ºС. Upon heating, continuous dehydration occurs between 160 – 250 ºС until the formation of amorphous products; crystallization above 450 ºС produces UO₂MoO₄, MoO₃, and UMo₁₀O₃₂. Below 250 ºС, thermal expansion of the compound is strongly anisotropic, with the maximal direction perpendicular to the plane of the layers.

The Tsagan-Shibetu earthquake 29.07.2022 with ML = 6.2, M_W=5.5, time UTC 13:01:10,1 occurred in the ridge of the same name in the east of the Gornyi Altai near the Tuva Basin (50.51º N, 90.69º E). In the twentieth century, this ridge was seismically inactive and neighbored seismically active ones: the focal area of the Ureg-Nur earthquake of 1970 with M_S=7.0 and the seismically active Shapshalsky ridge, where earthquakes with a magnitude of up to five often occurred, and there were no large earthquakes yet. After the Chuya earthquake of 2003 with M_S=7.3, significant changes occurred in the seismicity structure of Altai, after a lull, new zones of increased activity emerged, one of which is the Tsagan-Shibetu ridge. In the internal structure of the ridge, a focal area with a triple areal structure and with an impulse development of the process over time was formed. The formation of high ridge activity occurred in the presence of foreshocks.

The article presents new data on the structural position, mineralogy and geochemistry of ores for the Aliinsky ore cluster and their technological features. The mineralogical and geochemical zoning of the Verkhne-Aliinsky gold ore deposit and the entire Aliinsky ore cluster as a whole is characterized The subordination of local and horizontal zoning of mineralization within the node, localization of granitoids of the late phase of the Late Jurassic Akatuevsky complex is shown. A conclusion was made about the connection of mineralization with granitoids within the framework of a single ore-magmatic system that existed in unstable P-T-X conditions of shallow depths, transitional to near-surface. This distinguishes the Verkhne-Aliinskoye deposit from the Sredne-Golgotayskoye and Sosnovskoye deposits that are similar in composition and determined, partly, the technological resistance of its ores.

The article presents several published opposing points of view on the ore-controlling stage of the large (⁓ 2,000 t) Sukhoi Log gold deposit, as well as data from a detailed geological and structural analysis obtained by the authors. The deposit is located in the southern framing of the Siberian Craton in the black shale deposits of the Khomolkhin suite (610-600 Ma) on the territory of the Baikal-Patom folded belt. The complex regional structure of the Baikal-Patom belt formed as a result of the addition of the Baikal-Muya belt to the Siberian craton is demonstrated. The formation of industrial ores of the Sukhoi Log deposit and ore-controlling folding occurred in the Late Ordovician – Early Silurian (~ 450–420 Ma). The second stage of formation of weakly gold-bearing ores occurred in the early Carboniferous (340‒330 Ma). As a result of the conducted study, the absence of an ore-controlling fault zone of the syn-folded stage (450‒420 Ma) was established. It is shown that the internal structure of the gold ore zone is represented by intensively deformed rocks in the anticline core, where gold-quartz-pyrite veins occur in layers. It is concluded that the Sukhoi Log deposit is a classic example of disharmonious crumpling of plastic rocks in the core of an anticline, where signs of two stages of structure formation are combined: the longitudinal bending of a rock mass with the flow of matter and its (matter) laminar flow. Geological and structural studies of the deposit, together with previously published data, allow us to classify the deposit as an orogenic type, with a metamorphogenic-metasomatic of the redistribution of ore matter.

4D seismic exploration is a series of consecutive time-separated 3D areal seismic surveys at oil and gas fields under development. Its purpose is to attempt to register changes in productive formations caused by hydrocarbon extraction from the subsoil in the seismic wave field and, on this basis, optimize the scheme for further field development.

This article provides the first comprehensive analysis of the current state of 4D seismic exploration in Russia. Unfortunately, there are only a few cases of using this technology, while global experience already includes hundreds of successful examples. Various options for its implementation at sea and on land are considered. Almost all known cases of 4D seismic exploration application in Russia, which are still few, are given and the future prospects of this method are analyzed.

At pressures of 3.0 and 5.5 GPa and a temperature of 1200°C, metasomatic reactions involving garnet lherzolite and SiO₂-, Al₂O₃-, and alkali-rich supercritical fluids or melts have been experimentally studied. These fluids and melts could potentially be formed during the processes of dehydration, decarbonation, and melting of metasediments in subduction zones. The reaction of garnet lherzolite with model subduction mobile phase has been shown to lead to changes characteristic of modal metasomatism in the lithospheric mantle. As a result of the reaction with the melt at a pressure of 5.5 GPa, phlogopite-bearing garnet lherzolite is formed, while at a pressure of 3.0 GPa, phlogopite-bearing garnet harzburgite is produced. With an increase in the volatile content, primarily CO₂, in the fluid/melt at pressures of 3.0 and 5.5 GPa, the reaction proceeds through intense carbonation of peridotite, leading to the disappearance of olivine and the formation of orthopyroxene and magnesite, resulting in the transformation of lherzolite into carbonated pyroxenite. At a pressure of 3.0 GPa and a temperature of 1200 °C, a carbonate-silicate melt rich in alkalis is formed. Overall, the presence of a significant amount of dissolved CO₂ in a SiO₂-rich fluid or melt induces metasomatic transformations in peridotite that are very similar to those occurring during its reaction with carbonatite melts. Specifically, at a molar ratio of CO₂/(CO₂+H₂O) < 0.23, phlogopite is formed, while at >0.51, magnesite is produced. Phlogopite and magnesite do not form simultaneously in the products of metasomatic reactions.

The Laptev Sea sedimentary basin is located in the eastern part of the Russian Arctic shelf and has been fairly well studied by geophysical methods, but until recently, drilling data were lacking. In 2021, six new stratigraphic wells were drilled on the Laptev Sea shelf north of the Anzhu Islands by order of PJSC NK Rosneft. As a result, unique core material was obtained, which was studied using a wide range of analytical methods. This article is devoted to the analysis of the geochemical characteristics of the oil and gas source rocks (OGSR) of the Cretaceous-Cenozoic complex, which in the Laptev Sea basin can be considered as a potential for hydrocarbon generation. The paper presents the main pyrolysis parameters characterizing the proportion of free hydrocarbons in the rock (S1), oil generation potential (S2), maturity (Tmax), as well as the maceral composition of rocks and vitrinite reflectance (VR). As a result, it was established that carbonaceous and clayey-siltstone rocks of the Paleocene-Eocene complex are enriched in organic matter (OM) containing up to 20% of the lipid component and are capable of independently generating not only gaseous but also liquid hydrocarbons. Unlike the OM of the rocks of the Paleocene-Eocene complex, the OM of the Lower Cretaceous strata is at a much higher stage of transformation, which corresponds to the peak of the "oil window" and the beginning of the main phase of gas formation MK2-MK4. The accumulation of OM occurred in various lithofacies conditions; both humic type III kerogen and mixed type II-III kerogen are found in the rocks. Based on the drilling results and studies conducted in the section of the sedimentary cover of the aquatic part of the Laptev Sea, factual data on the characteristics of oil and gas source rocks were obtained for the first time, which can be used to predict the oil and gas potential of both the Laptev Sea basin and the entire East Arctic region.

The brine and long drilling core (4.8 m) of bottom sediments of the hyperhaline Maloye Yarovoe Lake were studied. For the first time, the detailed chemical composition of pore waters and microbial diversity of bottom sediments were studied along the section. A complex mineral composition of sediments was revealed, reflecting the evolution of salinity and changes in sedimentation conditions in the Holocene. In the upper horizons, the mineral composition of the sediment is dominated by halite, quartz, and plagioclase, while in the chemical composition, Na and terrigenous elements (Si, Al, Fe, K) are associated with greater salinity and a high level of lake waters, while in the lower intervals, an increase in gypsum, calcite, magnesite, as well as Ca, Mg, Sr, U, S_total, S (VI) is noted, which indicates a drop in salinity and the level of lake waters in the past. Authigenic minerals (pyrite, hydrotroilite, siderite, ankerite) are formed in reducing environmental conditions, in the process of bacterial sulfate reduction. Distribution of biogenic elements along the section is stratified: maximum TOC (up to 3.2%) and TN (up to 0.52%) in the upper sediment layers is associated with accumulation of OM of planktonic genesis, and a decrease with depth reflects destruction of OM during diagenesis and changes in the bioproductivity of the lake. In pore waters, in comparison with brine, an increase in the average contents of ions SO₄^2–, PO₄^3–, Ca²⁺ and dissolved elements — Si, Al, Fe, Mn, Mo — is noted. A trend is observed for a decrease in Cl^– concentrations with depth and an increase HCO₃^–, Ca²⁺, Sr²⁺, and Mn²⁺ in pore waters, which indicates some decrease in the salinity of lake waters and more intense processes of carbonate sedimentation.. Cyanobacterial mats play an important role in the biogeochemical cycles of the lake, they accumulate Zn, S and Mg in their composition, and their microbial communities (Pseudomonadota, Cyanobacteriota, Rhodothermota) create unique conditions for the formation of zinc sulfides, copper carbonates, as well as sulfides and intermetallics of noble metals (Ag-Au). Microbial processes play a key role in the formation of authigenic minerals and the destruction of organic matter during diagenesis.

Based on new sedimentological, lithochemical, and biostratigraphic data, the main part of the Inikan Formation, which is part of the Kuonamsky Complex of the Lower and Middle Cambrian on the Siberian Platform, has been characterized. Using an integrated approach, including textural analysis, study of the geochemistry of rock-forming oxides and organic carbon, lithochemical calculations, optical petrographic, and X-ray structural studies, a classification of carbonaceous rocks in the Inikan and Chay Formations has been proposed. This has allowed us to clarify the structure of the overall section and the conditions under which Cambrian deposits formed. For the first time, widespread influence of volcanic activity during sedimentation in the Kuonamsky Complex in the southeastern Siberian Platform has been identified. The distribution of paleoseismic breccia in the section has also been described, with horizons that represent good regional stratigraphic markers. Limitations in the use of the Strakhov module and the Nesbit-Young CIA index for characterizing sedimentation conditions of domanicoids have been revealed.