Research subject. This study focuses on the geodynamic processes occurring in two representative sectors of the Alpine Himalayan orogenic belt – Southern Tibet and the Greater Caucasus – which exhibit similar stress patterns under contemporary geodynamic conditions. Aim. To conduct an integrated analysis of tectonic scenarios and refine the understanding of stress strain distribution within the Alpine–Himalayan orogenic system. Materials and methods. Numerical modeling of the stress–strain state of the Earth’s crust was carried out. The simulation was conducted in an elastic formulation using the finite element method. Boundary conditions were defined based on geological and geophysical data, under the assumption of dominant horizontal compression typical of the present-day tectonic regime in the studied regions. Results. Numerical simulations were performed for two segments: the Himalayan region (Nepal) and the Caucasus (Greater Caucasus). The resulting spatial distributions of stress components revealed correlations with surface topography, seismic event density, seismic energy, and vertical crustal movement rates. Conclusions. The Alpine–Himalayan orogenic belt represents one of the longest and most tectonically active mountain-building systems on the Earth, formed through complex inter-plate interaction processes. Both regions are characterized by pronounced frontal compression, driven by the convergence of the Indian and Eurasian plates in the Himalayan segment and the Arabian and Eurasian plates in the Caucasus. Areas of anomalous stress concentration were identified, which may indicate areas of potential geodynamic hazard. The results demonstrate that both the Himalayan and Caucasus segments exhibit a common mechanism of stress localization near major fault zones, suggesting comparable geomechanical processes associated with continental collision in these regions.

Research subject. The Central Arctic Rise (CAR), including the Canada Basin, Northwind Ridge, Chukchi Plateau, Mendeleev Ridge, and Lomonosov Ridge. Aim. To explore the potential of gravimetric and magnetometric methods for studying the deep structure of the Earth’s crust and rock heterogeneities. Materials and methods. The VECTOR, POLE, and ADMITTANS methods developed by the authors were used. The first two methods are intended for interpreting potential fields in gravimetry and magnetometry, while the ADMITTANS method is a form of describing the general interrelationship of terrestrial processes, using the ratio of anomalous gravitational and magnetic fields and allowing for expanded application in geology. Results. A horizontal section of the North Pole gravity cube, the contour of the Central Arctic area, the junction of the Greenland, Eurasian, and North American plates, and the Mid-Atlantic Ridge were obtained, as well as a gravimetric section of the model compared to the velocity model of the Earth's crust and upper mantle along the deep seismic sounding (DSS) profile. Conclusions. The gravimetric map constructed using the VECTOR system is consistent with the European Moho seismic mapping model and is recommended for studying the internal structure of ridges, basins, islands, and other marine and land features. The ADMITTANS method reflects the Central Arctic uplifts with a significantly greater relief than gravity and magnetic field maps alone. The use of the POLE method is effective for localizing the sources of anomalies from structures, faults, and stepped basement features and is proposed for localizing, tracing, and refining the Moho boundary.

Research subject. A population of detrital zircon extracted from sandstones of the Bederysh Subformation of the Upper Riphean Zilmerdak Formation of the Southern Urals. Aim. To establish the distribution of U–Th–Pb (LA-ICP-MS) isotopic ages of detrital zircon of this straton, to compare the data obtained with those for the Biryan and Lemeza subformations of the same formation, to reconstruct sources of detrital material. Materials and methods. 120 detrital zircon grains were analyzed, 89 of which yielded concordant (≤10%) isotopic ages. U–Pb isotopic dating of zircon by LA-ICP-MS was performed at the Laboratory of Chemical Analysis Research of the Geological Institute of the RAS using an NWR-213 nanosecond laser ablation system (Electro Scientific Ind.) coupled with an Element2 high-resolution magnetic-sector ICP mass spectrometer (Thermo Scientific Inc.). Results. The studied population of detrital zircon is characterized by the age range from 3214 ± 21 to 1761 ± 21 Ma. Grains with an age of over 3200 Ma (Saamian) make up 1% of the entire sample, with an age of 3200–3000 Ma (Early Lopian) – 4%, ages from 3000 to 2800 Ma (Middle Lopian) – 8%, and an age of 2800–2500 Ma (Late Lopian) – 13% of grains. The proportion of zircon with an Early Karelian (2500–2100 Ma) age and the Late Karelian (2100–1750 Ma) is 43 and 30%, respectively. On the curve of the relative probability density of ages, the analyzed zircon crystals from the sandstones of the Bederysh Subformation form maxima of 2740, 2190, 2140, 2070, and 2010 million years. Conclusions. The comparison of the maxima in the relative probability density curves for the ages of detrital zircons extracted from sandstones of the Biryan, Lemeza, and Bederysh subformations of the Zilmerdak Formation suggests that, at the beginning of the Zilmerdak time, the main influx of clastic material into the sedimentation area came from Fennoscandia, while additional sources may have been located within Sarmatia. At the same time, the presence of an unknown closer source cannot be completely ruled out. During the accumulation of sands of the Lemeza Subformation, the supply of clastic material occurred primarily through the erosion of Volga–Ural rock complexes, while rock associations of Sarmatia and Fennoscandia played a secondary role. At the end of the Zilmerdak time, clastic material was probably transported into the sedimentation area primarily from Sarmatia; Fennoscandia and the Volga–Ural region may have served as additional sources of clastic material.

Research subject. This article presents new research data on the structural features of the Llandovery and Wenlock Series in the Bezymyannyj Formation section at the Chernov Uplift. Materials and methods. The research was based on a layer by-layer section descriptions and representative collections of sedimentary rock samples containing fossil fauna, as well as obtained isotope data (δ13Ccarb and δ18Ocarb ). Results. Changes in sedimentation environments and the distribution of various groups of faunal remains were identified, along with positive deviations in carbon and oxygen isotopes within a 51.5 m thick stratigraphic interval. This indicates a hiatus in sedimentation and an ecosystem reorganization at the Llandovery–Wenlock boundary. These changes coincide with the global biotic and isotopic Ireviken Event. Conclusions. The analysis of the taxonomic composition of the biota, as well as the distribution of carbon and oxygen isotope values in the boundary deposits of the Llandovery–Wenlock Series of the Bezymyannyj Formation, as well as the performed bio-chemostratigraphic correlation with coeval deposits on the island of Gotland, in Podolia, Estonia, and China, indicates an Early Sheinwoodian Ireviken Event in the Bezymyannyj section at the Chernov Uplift.

Research subject: This paper examines variations in the carbon isotopic composition of carbonate rocks from the middle Famennian part of the Iz’yayol River section (south of the Chernyshev Ridge, north-east of European part of Russia). Aim. To analyze the carbon isotopic composition of the carbonate rocks under study and assess the stratigraphic significance of the observed isotopic deviations. Materials and methods. The research was based a lithological analysis of 76 thin sections, a biostratigraphic analysis of conodonts from 51 limestone samples, and a geochemical analysis of 69 samples for δ¹³C_carb and 24 samples for C_org analyses. For micropalaeontological studies, the carbonate rocks were disintegrated in a 7–10% acetic acid solution using standard techniques. A series of screening tests was performed to determine whether the isotopic data preserve the primary isotopic composition of ancient seawater. Results. The middle Famennian succession of the Iz’yayol River section consists of siliceous, clayey-carbonate rocks, which formed in slope deep-water shelf conditions. This section spans the conodont zonal interval from the Lower crepida Zone to the Upper rhomboidea Zone and extends into the Upper marginifera Zone. Near the base of the Lower marginifera Zone, a negative shift in the carbon isotopic composition (≈1.5–2‰) and a subsequent positive shift (≈4‰) was established; these shifts are also identified in different facies of geographically significantly distant sections of Central and Eastern Europe, East and Southeast Asia, North America, and Australia. Conclusions. The negative δ13C_carb isotope shift near the base of the Lower marginifera Zone along with the subsequent positive shift in the Lower marginifera–Upper marginifera zonal interval can be used for solving stratigraphic problems within the Timan–North Urals region. The subglobal/global character of these isotopic deviations indicates their potential for interregional stratigraphic correlation.

Research subject. Lower Bashkirian carbonate deposits exposed along Sharyol’ Creek, Ilych River Basin, Northern Urals. Material and methods. The study was based on a field description of the section conducted in the summer of 2022 and the examination of 14 samples by conventional optical microscopy. Selected samples were analyzed for conodonts using the standard method of dissolving carbonates in a 10% acetic acid solution. Results. The studied section with an exposed thickness of 33 m is composed of carbonate rocks of both marine and pedogenic genesis. Two foraminiferal associations were identified: the Eostaffella association characteristic of quiet shallow-marine environments and the Pseudoglomospira association corresponding to coastal shoal facies. The occurrence of carbonate paleosols enriched in Ba, along with the widespread presence of authigenic quartz crystals and ratovkites, indicate a semi-arid climate during the Early Bashkirian. Analysis of the identified lithologies indicates the presence of fragments of two sequences. Conclusions. The studied section is interpreted as representing a shallow-marine island system that developed predominantly in a quiet-water marine basin. It is assumed that the basin was protected by shallow-water barrier systems (marginal sand shoals, brachiopod banks).

Research subject. The clayey strata of the Tavda horizon were formed as a result of the third, final major cycle of marine sedimentation in the Siberian-Turgai subregion. During the Paleogene period, the Turgai Trough functioned as a meridional strait, supporting maritime communications between the basins of the Paleoarctic, Western Siberia, and the Turan Sea. Maritime communication was occasionally interrupted during the Eocene epoch. Reliably dated sediments on the Kustanai Saddle make it possible to identify periods of active functioning of the Turgai Strait. Aim. Biostratigraphical study of the Belinskiy sequence and the Tavda Formation in the northern part of the Turgai Trough, which allows for detailed dating of deposits, characterization of marine sedimentation environments, and correlation of remote sections. Results. A biostratigraphic subdivision of the Middle Eocene deposits was carried out based on the study of dinoflagellate cyst assemblages (organic-walled microphytoplankton) and the identification of interval zones in a series of quarries and boreholes in the studied region. The established zones – (1) Phthanoperidinium regale–Phthanoperidinium clithridium and (2) Enneadocysta arcuata – indicate the onset of a marine sedimentation regime during the Lutetian of the middle Eocene. The active marine regime ended with a sharp shallowing of the basin with the formation of azollae biofacies and the closure of the “Turgai gates” in the middle Lutetian. Conclusion. Zonal species of planktonic organisms enable subglobal geological correlation of sections of Northwestern Europe, the Siberian-Turgai subregion, the Russian platform, and Mountainous Crimea. Key events in the emergence of endemic Siberian marker species were established, allowing detailed correlation of coeval marine sediments in the Trans-Ural structural-facies zone, the Turgai Trough, and the Chelkar depression. Endemic species of dinoflagellate cysts indicate the formation of a closed basin on the West Siberian Plate during the Lutetian. Marine sediments of Bartonian and Priabonian age have not yet been identified on the Kustanai Saddle.

Research subject. Accessory minerals that contain REE, Zr, and Nb in vein granites, plagiogranites and the host amphibolites of the western Ufaley Block (Southern Urals). Aim. To study the chemical composition of rocks and the species diversity of their accessory minerals, localized within the large, complex geochemical Nizhneufaley–Takhta Nb–Ta–Zr–Y anomaly. Materials and methods. Petrographic description of the rocks, determination of their chemical composition and geochemical features, microprobe analysis of the mineral composition and their typification. Results. The principal hosts of Nb, Zr, and Y were found to be rutile, titanite, zircon, and xenotime-(Y), while REE, Th, and partly Y are hosted by minerals of the monazite group and the epidote supergroup (REE-rich epidote, allanite-(Ce)), transformed to varying degrees. The latter, allanite-(Ce) in particular, are readily altered to form pseudomorphs consisting of mixtures of various minerals, the compositions of which are determined by calculating normative mineral constituents (minals). The pseudomorphs were found to consist of cerianite (or bastnaesite-(Се)), monazite-(Ce), florencite-(Ce), Ce and Th-titanate, huttonite, and an Fe–Al–Si mixture. Conclusions. It is assumed that the conditions of repeated tectonic-thermal activity and subsequent near surface processes promoted the accumulation of accessory rocks containing Nb and Y, as well as well as newly formed Ce- and Th-enriched phases derived from allanite-(Ce). This likely explains the development of the extensive geochemical anomaly as a result of the primary enrichment of the studied rock types in rare elements, characteristic of plume-dependent series.

Research subject. Native gold occuring in various rock types (rodingites and related albite-amphibole rocks of fibrous structure, such as nephritoids, serpentinites, talc–carbonate and magnetite–chlorite–carbonate rocks, carbonate–chrysotile veins) associated with ophiolite ultramafics of the Urals and Siberia, as well as spatially associated placer deposits. Aim. To expand the existing data on the copper isotopic composition of native gold and to identify the main patterns of its variations in mineralization associated with various types of metasomatic alteration of ophiolite ultramafic rocks. Methods. The copper isotopic composition of native gold grains was analyzed by selective chromatographic separation of copper from sample solutions, and subsequent determination of the ⁶⁵Cu/⁶³Cu value using a Thermo Fisher Neptune Plus MC ICP-MS at the Collective Use Center “Geoanalitik” of the Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences. Results. The copper content in native gold varies from a few tenths of a percent (carbonate-clinochrysotile veins with demantoid, talc-carbonate rocks, foliated antigorite serpentinites) to a few percent (magnetite-chlorite-carbonate rocks) and higher values characteristic of gold–copper intermetallics (tetraauricupride AuCu and auricupride Cu³Au) in rodingites, nephritoids, antigorite serpentinites, and gold-magnetite ores. All the samples exhibit δ⁶⁵Cu values that range from –1.23 to +0.73‰ with a total variation of about 2‰. No differences in the copper isotopic composition relative to the copper content in native gold were revealed. The δ⁶⁵Cu values of Au–Cu intermetallic compounds range from −0.85 to +0.51‰; the δ⁶⁵Cu values for Cu-bearing Au–Ag alloys vary from −1.23 to +0.73‰. The δ⁶⁵Cu values range from −0.2 to +0.51‰ for gold from rodingites and nephritoids, whereas for zones of foliated serpentinites and magnetite–chlorite–carbonate rocks they vary from −1.23 to +0.73‰. Copper-rich gold from placers is characterized by negative δ⁶⁵Cu values (from −0.01 to −0.83‰). Conclusions. Variations in δ⁶⁵Cu values in native gold from various types of gold-bearing rocks in ophiolite massifs fall within a range close to the δ⁶⁵Cu value of the Bulk Silicate Earth (0.06 ± 0.20‰), indicating that the source of copper was controlled by a deep reservoir, from which copper and gold were extracted by reduced fluid. During the evolution of mineral formation, when ultramafic massifs were transported toward their present position, the copper isotopic composition of the fluid and the Cu-bearing minerals that inherited the composition of the fluid deviated from the zero value in the original source due to the transition of certain part of copper from a reduced to an oxidized state. Under hypergene conditions, native gold inherits the copper isotopic composition of its bedrock source. The effect of hypergene processes on the Cu isotopic composition, expressed in the formation of high-fineness rims on native gold grains, is negligible.

Background. The formation of boninites and high-magnesian andesites is associated with the early stages of island arc evolution, when melting of the hot, depleted peridotite mantle occurs. Their formation in other geodynamic settings, such as continental rifts and back-arc basins, requires additional or alternative sources of matter and magma generation mechanisms. The boninite-like high-magnesian rocks, which we identified within the igneous complexes of a mature island arc, suggest that they may have formed through magma mixing. Research subject. Boninite-like rocks of the Middle Devonian age of the Rudyanskaya basalt–andesite–dacite stratum (the southern part of the Alapaevsky block as part of the Alapaevsko–Adamovsky structural-formational zone of the East Ural megazone). Methods. The contents of petrogenic oxides were determined by X-ray fluorescence analysis using CPM-18 and EDX-900HS instruments; the contents of rare elements were determined by ICP-MS using an ELAN 9000 analyzer. The mineral composition was analyzed using a Mira Tescan S6123 electron scanning microscope with an INCA Energy 450 X-Max 80 EDS attachment. Results. According to the standard classification diagrams based on chemical composition, the high-magnesian basaltic andesites and andesites of the Alapaevsk block indicates belong to boninites. The rocks are rich in Si (52–54 wt % SiO2 ), Mg (9–11 wt % MgO), Cr (340–1050 ppm), Ni (130–400 ppm), with a low content of Ti (0.43–0.48 wt % TiO2 ). Groundmass microcrysts are composed of more basic plagioclase (An₆₃ ) and more magnesian clinopyroxene (mg# – 0.81–0.88). The latter, in addition to the microcrysts, forms rims around phenocrysts of orthorhombic and monoclinic pyroxene. Such relationships between minerals and their compositions indicate mixing of basic and felsic melts. The basic melt was dominant and was enriched in Mg, Cr, and Ni, with the magnesia value exceeding 0.7. Olivine and magnesiochromite, whose compositions are consistent with picrobasalt or basalt, crystallized on its liquidus. The felsic melt was close in composition to dacite. It produced an association of plagioclase, clinopyroxene, orthopyroxene, and titanomagnetite phenocrysts. Its magnesia was approximately 0.4. The crystallization temperature of clinopyroxene phenocrysts was approximately 1100°C. The hybrid melt obtained during mixing, with a magnesium index of approximately 0.7, began to crystallize at approximately 1170°C, 60–80°C higher than the temperature of the phenocrysts. The position of the studied rocks on the MgO–SiO₂ classification diagram are consistent with the mixing of mafic and felsic magmas, which resulted in the formation of rocks with boninite characteristics. On the Ta/Yb–Th/Yb geotectonic diagram, their position is far from the field of typical boninites and their differentiation products (high-magnesian andesites) corresponding to compositions characteristic of volcanic rocks in developed island arcs, where they are located. Conclusion. The results suggest that magma mixing is a plausible mechanism for the formation of magmas with boninite characteristics.

Research subject. Chromium-bearing garnets from the wollastonite–garnet–diopside skarn of the Yoko–Dovyren layered dunite–troctolite–gabbro intrusive. Aim. To study the morphology and material composition of chromium-containing garnets from the wollastonite–garnet–diopside skarn and diopsidite contact zone of the Yoko–Dovyren layered massif. Materials and methods. The study was based on several rock samples collected from the wollastonite–garnet–diopside skarn and the diopsidite contact zone. The methods of optical microscopy, scanning electron microscopy, X-ray spectral microanalysis (local), and X-ray phase analysis were used. Results. The highest proportion of chromium-bearing garnet occurs in the rock adjacent to the diopsidite contact, where its content reaches 30 wt %. Diopsidite and the skarn contact zone contain significantly less garnet, with an abundance of approximately 5 wt %. The thickness of this zone is about 1 cm on both sides of the contact boundary. All studied garnets belong to the uvarovite–grossular–andradite solid-solution series and contain minor amounts of pyrope and almandine components. In the early-stage rocks, grossular is generally the dominant end-member, whereas in the later-stage rocks, andradite predominates. The latter is commonly enriched in impurity elements. No systematic relationship was identified between garnet crystallographic morphology and the chemical composition of the host rocks. However, the occurrence of elongated and atypical garnet forms is attributed to xeromorphic growth conditions resulting from late-stage crystallization. Garnets from diopsidites are characterized by idiomorphic crystals, often exhibiting well-developed crystallographic faces. A correlation was established between the Fe content of garnet and the composition of the host rocks: iron-rich garnet forms in Ca-rich rocks, whereas garnet with lower Fe contents occurs in diopsidites. The composition of garnet and its position within the uvarovite–grossular–andradite solid-solution series reflect the composition and physicochemical conditions of the mineral-forming fluids and metasomatized rocks. The formation of the mineral assemblage was controlled by high-temperature diffusive metasomatism followed by retrograde low-temperature metasomatic processes.