-Years after the Chuya earthquake of 2003, geological structures adjacent to the focal area of the Chuya earthquake are still seismically active. The Aigulak focal area is one of them, but energetically the most pronounced. Detailed studies have been carried out with the network of stations of the Altai seismological testing site, supplemented by temporary stations. The region activated in the form of a local and compact structure measuring 10 x 10 km with focal depths from the first 100 m to 20 km. The focal area is not a subsequent activation along the same fault with the Chuya earthquake, but is located on a subparallel fault in the nodal region with its branching into three faults. The seismic activation of the Aigulak focal area is not an aftershock process after a major earthquake, but is an activated structure with a dynamically changing seismic process. An intensive process has formed since the earthquake in 2012 with ML = 6.1 with a gradual decrease in the number of earthquakes, and in 2019 the Aigulak earthquake with ML = 5.5 occurred with a very strong aftershock process after it. Our results of an area study of earthquake density in the focal zone indicate a change in the regime over time: from chaotic to self-organizing along short faults. We conclude that the focal area has not reached the maximum level of seismic energy release.

The reconstruction of the Early Paleozoic collision metamorphism of the Khan-Khukhei Block (Northern Mongolia) based on 3D modeling of thermal state of the crust and isotope dating is presented. The age of garnet–biotite schist from a metamorphic complex of the Khan-Khukhei Block of 517.4 ± 7.4 Ma is determined for the first time. 3D modeling was conducted to compare this age of metamorphism with the available age determinations of (post-) collision granite formation in the range of 513‒505 Ma. The model considers radiogenic heating at an elevated heat production of rocks of the thickened crust of the Khan-Khukhei block as the cause of the migmatization and granitoid melts formation. 3D modeling was conducted for the first time for thermal-dome type of metamorphism. The results provide a realistic conception of magma generation in typical collision settings in the absence of mantle magmatic heat sources. The time interval between metamorphism and the stage of anatectic magma formation is 5–12 Ma.

We report study results of basic intrusive bodies in the middle Paleozoic Vilyui paleorift (eastern Siberian Platform). Geochemical data for basic sills penetrated by boreholes in the rift's dike swarms are presented, as well as our data on the time of formation of sills and dikes. We also studied mineral-hosted melt inclusions from a dolerite dike of the Vilyui-Markha dike swarm on the northwestern flank of the Vilyui paleorift. Data on the compositions of homogenous glasses of mineral-hosted melt inclusions yielded the P-T parameters of mantle sources of basic melts responsible for the formation of the Vilyui paleorift gabbro-dolerites. Two depth levels of basic melt generation have been established: 95-65 km at 1480-1400 degrees C and 55-45 km at 1360-1320 degrees C. Crystallization of the melts occurred at a shallow depth of 12-4 km with a decrease in temperature from 1185 to 1125 degrees & Scy;. This occurrence of basic melt sources at two different depths, as well as the heterogeneity of the chemical composition of melt inclusions and their host minerals explains the presence of two pulses of Devonian basic magmatism. Our new numerical thermomechanical model of magma rise during melting of the lithospheric mantle above a mantle plume supports the existence of two chambers at the spinel-garnet peridotite boundary and under the base of the crust, as well as the two-stage nature of Devonian magmatism.

Consideration is being given to the geochemical composition of the rocks, representing the hidden part of the volcanic and intrusive material in the structure of the Yenisei-Khatanga Trough (YKT), in relation to its belonging to a large igneous province (LIP) of Siberia. The geochemical characteristics of mafic rocks, presenting in the sedimentary complexes of the YKT, correspond to three types of mafic rocks allocated to the Siberian LIP: Nadezhdinsky (low Ti), Morongovsky (low Ti), and, in limited quantities, Ivakinsky (rift-related high Ti). Based on the seismic data, there was constructed a deep structural-tectonic cross-sectional model, and there was considered the position of mafic intrusions in the sedimentary section in the western junction zone of the Siberian Platform and the Kara (Taimyr-Severozemelsky) orogen. The seismic data show an anomalous area in the lower crust and at the crust–mantle boundary immediately below the YKT depocenter, whose seismic section is characterized by a chaotic scattered wave field with no reflective boundaries.

Based on the proposed numerical model of the stress-strain state of polymineral rocks, which describes the formation of blastomylonites in the Yenisei Regional Shear Zone (PRSZ) in the Yenisei Ridge, the possibility of local tectonic overpressure exceeding the lithostatic pressure in rocks subjected to shear deformations is shown. For tectonites of the southern (Angara-Kan block) and northern (Isakovka terrane and Garevka complex) segments of the PRSZ, estimates of the maximum overpressure were obtained from 2–3 to 4–5 kbar, which range from 25 to 50% of the lithostatic pressure. It is shown that excess pressures can be preserved in a local volume on a geological time scale sufficient for their fixation in metamorphic minerals. Model values of overlithostatic pressure in garnet-amphibole tectonites and geobarometric estimates of peak values during stress metamorphism allow us to offer new evidence of pressure inhomogeneity in natural mineral associations. Using the results of numerical modeling for the evolution of fault metabasite blastomylonites, it was established that the overpressure at the stage of syn-deformation metamorphism in the shear zone are possible at temperatures up to 600–650°C and not reaching 800°C; the presence of fluid or partial melt prevents the occurrence of overpressure. The amount of excess pressure due to shear stresses depends on the mineral composition and structure of the rock.

The formation mechanisms of sedimentary basins are considered as a response of deep processes in the mantle, therefore they carry important information about the geodynamics and thermal regime of the lithosphere. For different sectors of the northern margin of the Siberian Platform, the dynamics of sedimentation and subsidence was reconstructed. The analysis of subsidence curves shows that during the Late Paleozoic the sedimentary infill formed in the foreland basin environment. In the Late Permian-Early Triassic time, in the central and western sectors, the subsidence was accelerating due to the development of a thick trap complex; after the Permian and Triassic boundary the subsidence slowed down. During the period of trap magmatism, an anomalously high subsidence rate up to 4.8 km/Ma in the central and up to 0.5-1.1 km/Ma in the eastern and western parts was reconstructed. The high rate and short duration of accumulation of volcanogenic sediments can be explained by an episode of short-term extension under the influence of a plume, followed by a long period of thermal subsidence. Numerical modelling of the temperature regime near mafic intrusive bodies was carried out, which showed that when determining the paleoheat flow, the influence of trap intrusions can be traced up to 400-500 m from the contacts. Estimates of the paleoheat flow for the Permian-Triassic stage of tectonic evolution of the eastern sector were obtained. It was calibrated using the PetroMod software package, based on laboratory measurements of modern values of vitrinite reflectance for rock samples from wells, modern temperature and heat flow in the sedimentary cover. It was determined that trap magmatism occurred at temperatures increased to 100 mW/m2, while the mantle component of the heat flow reached 38-72 mW/m2; it is several times higher as compared to modern one. The obtained paleoheat flow estimates for the Late Permian-Early Triassic stage appear to correspond to anomalously high values of modern continental rifts.

Using 3D numerical modeling, we analyze the formation of postcollisional granitoids of the Kara orogen in Northern Taimyr under conditions of elevated heat flow due to the orogen’s breakup prior to its mantle plume episode (280–250 Ma). The initial geometry of the model area, the boundary conditions and physical properties for the crust and the mantle have been selected to reflect the structure of the crust in the junction zone of the Kara, Central Taimyr, and Siberian blocks. Comparing 2D and 3D modeling results with identical parameters and physical properties defined by the Rayleigh number shows that 3D modeling yields a more realistic and correct description of relevant magmatic processes. At the base of the modeled Earth crust an area of melting at a depth of 46–50 km appears, possibly with slight input of mantle component, which induces magma uplift and the formation of closely spaced granitoid intrusions. Plutons with diameters 10–20 km were emplaced at depths 14–8 km during 15 million years, which is close to the actual geological position and timing of postcollisional stocks of the Kara orogen.

This paper is concerned with the influence of the large (ML = 6.9) 2021 Hubsugul earthquake on the seismicity of the block structure in the junction area between the Altai–Sayan mountain region and the Baikal Rift Zone. This study uses data from the networks of seismic stations operated by the Altai–Sayan and Baikal branches of the RAS Geophysical Survey, as well as from Mongolian stations. We show the evolution of the seismic process near the boundaries of the Tuva–Mongolia block and adjacent blocks in eastern Tuva. We have determined and studied the source zone of the Darkhad earthquake swarm which was formed in 2022‒2023 as several sequences of events, with the larger ones having magnitudes ML > 5. Simultaneously with the activation of the Hubsugul earthquake source zone, we observed high seismic activity in the source zones of past large earthuuakes: 1991 Busingol, 2011‒2012 Tuva events, and 2008 Belin-Bii-Kham. The action of the Hubsugul earthquake on the seismicity in boundary blocks of the Altai–Sayan and Baikal zones was different from that of the 2003 Chuya earthquake on Altai seismicity.

We present a tectonothermal model showing the evolution of magmatism during the late Paleozoic postcollisional (pre-plume) development stage of the Kara orogen in northern Taimyr, Central Arctic. The model is based on new and published structural, petrologic, geochemical and geochronological data, as well as thermophysical parameters obtained for the Kara orogen that includes large amounts of syncollisional and postcollisional granites that formed due to the collision of the Kara microcontinent and the Siberian craton. Based on geological, geochemical and U–Th–Pb isotope data, the granites have been divided into syncollisional and postcollisional intrusions formed at 315–282 and 264–248 Ma respectively. Our previously published tectonothermal model [1] concerned the syncollisional formation stage of the Kara orogen at 315–282 Ma, during which the emplacement of anatectic granites took place. In this new study, we focus on the evolution of postcollisional magmatism in the orogen at the Permian–Triassic boundary. The existence of multiple bodies of allochthonous granitoids aged 265–248 Ma in the Kara orogen that predate the extensive eruption of the Siberian traps ( 250 Ma) motivates us to reconstruct the thermal state and melting mechanisms of the crust on the “pre-plume” stage. To solve this problem, numerical modeling of the thermal, tectonic, and magmatic evolution of the Kara orogen’s crust is used alongside geochemical and isotope data that reflects the magmatic sources of the granitoids.

The unusual composition of the protolith, its structural and textural heterogeneity, limited mass transfer and high temperatures are the causes of rare mineral formation and mineral associations during metamorphism and metasomatism. Most often, this is observed in shallow conditions (pressure up to 3 kbar) when additional heat is supplied to the rocks by magmatic intrusions. In the article, these issues are discussed on a number of geological complexes, in which the manifestations of metamorphism with the development of rare minerals and mineral associations have been studied in detail.

The reasons for the formation of rare minerals and mineral assemblages during metamorphism and metasomatosis are found to be the atypical composition of the protolith, the structural–textural heterogeneity, restricted mass transfer, and high temperatures. This is often observed under shallow conditions (pressure up to 3 kbar) during additional heating of rocks by igneous intrusions. In this paper, these questions are discussed with a series of domestic examples, the processes of mineral formation in which are studied in detail.

A model for the formation of intrusions of the collision stage of 525–490 Ma and a model of magmatism of the transtensional shear stage of 465–440 Ma within the Mugur-Chinchilig and Erzin-Naryn blocks of Western Sangilen (Tuva) have been developed to describe the process of crust-mantle interaction. Model experiments confirm petrological data on the presence of multi-level chambers during the formation of the Pravotarlashkinsky and Bashkymugur massifs. The proposed model describes the migration of mantle magmas above the head of the mantle plume at the collision stage and assumes the rise of magmas along a permeable tectonic zone in the mantle lithosphere and crust at the transtensional-shear stage. The modeling results allow us to establish that material from the magma chamber can reach depths of the upper crust in the volume ratio of gabbroids to diorites from 1 : 2 to 3 : 4 and additionally introduce about 5 % of the volume fraction of lower crustal material. The physical parameters of the primary magmas (viscosity, solidus and liquidus temperatures, degree of melting depending on temperature and composition, change in density) were calculated taking into account the real geochemical characteristics of igneous rocks from the polyphase massifs of Western Sangilen.

The paper presents a reconstruction of metamorphic stages in the Moren and Erzin metamorphic complexes in the Khan-Khuhay block of northern Mongolia. This reconstruction is used as a basis for discussing the general geodynamic history of the Sangilen terrain of the Tuva–Mongolia Massif. The calculated clockwise P–T path shows two stages of metamorphism: (1) collisional metamorphism at 9 kbar, 740°C; and (2) metamorphism related to a regional magmatic episode, at 6–7 kbar, 860–880°C. Geochemical and petrological features of rocks in the Khan-Khuhay block demonstrate that these rocks are similar to those of the metamorphic block of Western Sangilen in southeastern Tuva. Quartz monzodiorite intrusive bodies first found in the Khan-Khuhay block show geochemical features similar to those of Ordovician gabbro–monzodiorite intrusions in the western Sangilen. The Khan-Khuhay quartz monzodiorite intrusions may be small apophyses of an intermediate deep crustal magma chamber and could be a probable thermal source of metamorphic stage M2 in the Khan-Khuhay block. The numerical thermo-mechanical model of metamorphism in the Khan-Khuhay block explains the heating in the thickened crust during collision by a higher (relative to the average crustal) radiogenic heat production of 1.52 μW/m3. Computer modeling indicates that the P–T parameters of the second metamorphic stage could be reached only with the involvement of magmatic heat from the monzodiorite intrusion. The P–T metamorphic parameters calculated using mineral thermobarometry, similarity of geochemical characteristics, and results of the thermomechanical modeling allow us to conclude that the Erzin and Moren complexes have undergone a joint tectono-metamorphic evolution.

. Geological examples of the development of thermal dome structures in the Svecofennian belt demonstrate the relationship between plutonic and metamorphic events and metamorphic strengthening towards the core parts of the structures. The corresponding 2D geological model has been created to make a quantitative assessment of the effect of mantle magmas temperature at the base of the crust and the formation of the diapiric cores surrounded by high-temperature areas with a degree of granulite facies metamorphism. Modeling shows that there is a possibility of melting of the lower crust in the presence of a water fluid under the influence of mantle magmas. After melting, there occurs an ascent of partially molten material towards the upper crustal levels. An absorbed aqueous fluid changes to hydrous melt, thus lowering its viscosity and density. The ascending height of high-temperature cores is determined by the depth of viscous-to-elastoplastic transition in the crustal matter rheology. These materials ascend to upper levels in a partially molten state in the process of overthrusting due to "collisional" tectonics.

The results of an experimental study of seismic vibrations at the site for the construction of the Siberian Ring Photon Source (SKIF), which is a synchrotron radiation source of the fourth plus generation at 3 GeV and a perimeter of 480 m, have been considered. Seismic vibrations are a hindrance that reduces the accuracy of the experimental setup when studying materials with precision accuracy and resolution. The experiment was performed with broadband seismological equipment used at seismological stations. Seismic vibrations from different types of sources have been investigated: natural and man-made earthquakes, industrial explosions, noises of automobile and railway transport, vibrations from industrial equipment at enterprises located away from the facility under construction. Natural earthquakes create the strongest broadband impact on the site. Man-made earthquakes in the area of the Gorlovka coal basin can create short-term strong seismic impacts. Industrial explosions in terms of the seismic impact on the site are significantly inferior to the effects of earthquakes and are characterized by a more limited spectral composition of vibrations. The noises of motor transport cover frequencies from 4 to 30 Hz and quickly fade away along the site with distance from the road. Railway noises have the characteristic appearance of a set of multiple harmonics covering a wide frequency range with a duration of up to 10 min. Monochromatic signals from the operation of industrial equipment on and off the site are recorded at the site. At the same time, both continuous signals and those that occur episodically are recorded. A special class consists of monochromatic oscillations with a slowly varying frequency. The information on the level, spectrum, and duration of seismic vibrations necessary for calculating the seismic protection of the SKIF Central Research Center during its creation and development of a seismological monitoring system that compensates for the seismic effect on the accuracy of experiments was obtained.

Melt inclusions in the minerals from a dolerite dike of the Vilyui–Markha dike swarm, located on the northwestern shoulder of the Vilyui paleorift, have been studied. Data on the composition of homogeneous glasses of melt inclusions in minerals made it possible to establish the PT parameters of mantle sources of primary deep melts responsible for the formation of gabbro-dolerites of the Vilyui paleorift. Two levels of generation of the initial melts have been established for dolerites: in the intervals of 95–65 km at 1480–1400°C and 55–45 km at 1360–1320°C. The presence of two intermediate chambers in the crust, where melts crystallized, was identified at depths of about 12 and 9–4 km with a decrease in temperature to 1175–1125°С. The two-level arrangement of centers of magma generation, as well as the heterogeneity of the chemical composition of the minerals studied, makes it possible to explain the presence of two pulses of Devonian basic magmatism.

We present a tectonothermal model for the late Paleozoic syncollisional formation stage of the Kara orogen in northern Taimyr in the Central Arctic. The model is based on new and published structural, petrological, geochemical, and geochronological data, as well as thermophysical properties obtained for the Kara orogen. The latter hosts a significant volume of granites formed as a result of the collision between the Kara microcontinent and the Siberian craton. Based on geological, geochemical, and U–Th–Pb isotope data, the granites were differentiated into syncollisional and postcollisional intrusions that were emplaced in the intervals 315–282 and 264–248 Ma, respectively. The presented tectonothermal model covers only the syncollisional formation stage of the Kara orogen, during which anatectic granites formed. The 2D models help to reconstruct the main tectonothermal processes of the syncollisional stage of formation of this structure, taking into account the local peculiarities of the thermal state of the Earth’s crust in the region. The model shows the mechanisms of increase in the lower crust temperature necessary for the formation of syncollisional anatectic granites. The estimates obtained from the model constrain the time interval between collision/tectonic stacking and the granite formation. The modeling also showed the general regularities typical for orogens on syncollisional stages.

Marly limestone, marble, and gabbro-dolerite samples from the Kochumdek contact aureole are studied in order to estimate to which degree the spunite-merwinite (T = 750-900 degrees C) metamorphism at the site was isochemical. The 3 m wide zoned Kochumdek aureole is located at the contact between the Early Triassic trap intrusion of the Kuzmovka complex (v beta T1kz) and the overlying Llandovery marine marly limestones (S1ln) of the lower Kochumdek subformation in the right side of the Kochumdek River (tributary of the Podkamennaya Tunguska, East Siberia). The Kochumdek rocks are remarkable by the lack of prominent skarn or vein mineralization in marbles and autometasomatism in gabbro. The samples have been analyzed for major, chalcophile, rare-earth, and high-field strength elements. The Kochumdek marbles and marly limestones share similarity in major-clement patterns that record mixing of fine siliciclastic material with biogenic and chemogenic CaCO3 components. The major-element chemistry of marly limestones has been controlled by the compositions of fine elastic material transported from the provenance (Trans-Angara part of the Yenisei Ridge) and by the deposition environment of the early Silurian marine basin. The contents of Cu, Ni, Co, V, Mo, Se, Cr, and U in marly limestones and marbles correspond to marine sediments deposited in a low-productive oxigenated environment. The Ni/Co, V/Cr, Cu/Zn, V/(V+Ni), and U/Th ratios in spurrite marbles at the intrusive contact remain within typical limestone ranges but differ from those in gabbro, which have higher V and Cu enrichment and moderate contents of Zn, Ni, and Co. Marly limestones and spurrite marbles show identical REE+Y patterns and average Sigma REE contents. The major- and trace-element similarity between marbles and the protolith limestones, along with the absence of gabbro geochemical signatures in the metamorphic rocks, indicate that the thermal metamorphism was nearly isochemical. reactions occurred without any large-scale transport of major and trace elements across the sill/sediment boundary. The conditions were unfavorable for metasomatic alteration due to low fluid saturation of the Kochumdek intrusion and its structural setting, as well as to the lithological, mechanical, and thermal properties of the sediments.

The results of the 40 Ar / 39 Ar dating of the vein material of pseudotachylite from the deformation zone of the Main Anabar fault (Northern Yakutia) are presented. The depth of formation of pseudotachyllites is reconstructed using the principles of thermochronology and rheological parameters of deformation. Their 40 Ar / 39 Ar age (1910 ± 24 Ma) is compared with the stages of formation of the main deformation belts of the Anabar Shield. A thermochronological interpretation of the results obtained is given. A method for estimating the depth of deformations and the magnitude of differential stresses is proposed.

The results of the 40Ar/39Ar dating of the vein material of pseudotachylite from the deformation zone of the Main Anabar fault (Northern Yakutia) are presented. The depth of formation of pseudotachylites is reconstructed using the principles of thermochronology and the rheological parameters of deformation. The 40Ar/39Ar age (1910 ± 24 Ma) is compared to the stages of formation of the main deformation belts of the Anabar Shield. A thermochronological interpretation of the results obtained is given.