The Northern Timan is an uplifted block of Late Precambrian basement of the Timan Ridge, where Neoproterozoic sedimentary-metamorphic rocks of the Barmin Group are cut by intrusive rocks of different composition and all unconformably overlain by Lower Silurian limestone. To determine the age of granites, U-Pb dating of zircons was carried out using secondary ion mass spectrometry (SIMS). Two episodes of Neoproterozoic granite magmatism were established. Granite rocks of the Bolshoy Kameshek (613 ± 6 Ma) and Cape Bolshoy Rumyanichny (614 ± 11 Ma) plutons are interpreted to be associated with the formation of Central Iapetus Magmatic Province and record the Ediacaran stage of Rodinia breakup. The granites of the Sopki Kamennyie pluton (723‒727 Ma) formed in Cryogenian time and are assumed to represent an earlier episode of Rodinia breakup. Their ages correlate with the age of the Franklin LIP that existed in Northern Laurentia and is believed to have spread to South Siberia.

Among the Riphean–Vendian dyke complexes of the basic composition, which intersect the Precambrian strata of the Bashkirian meganticlinorium (Southern Urals), one of the most common is the Kurgas gabbro-dolerite complex dated to the Early – Middle Riphean. This article presents the isotopic dating, petrological and geochemical features of the rocks belonging to the Kurgas complex. It gives the first description of the regional geochemical zoning that is reflected in a decrease in SiO₂ contents from the north to the south along the Bashkirian meganticlinorium, and an increase in MgO contents in the same direction, which is attributed by the authors to an increase in the permeability of the crust to the south during opening of the Mashak riftogenic structure.

New data on isotopic ages were obtained for the dyke that cuts the Satka formation of the Lower Riphean – 1318±10 (⁴⁰Ar/³⁹Ar), the intrusion in the exocontact zone of the Berdyaush rapakivi granite massif – 1349±11 Ma (U-Pb), and the andesite dyke among the metamorphic rocks of the Taratash complex – 1365.6±6.6 Ma (U-Pb). These ages, in combination with the previously obtained data, suggest that the complex formed during a rather long period of time (from 1385 to 1318 Ma, as a minimum), which corresponds to the beginning of the Middle Riphean. Isotopic U-Pb age of the dyke that cuts the contact zone of the Berdyaush massif, suggests that the major portion of the massif had already crystallized by that time and was exhumed into the shallow zone of brittle deformation.

The article presents the results of geological and structural studies of the northwestern part of the Gargan quartziferous province, wherein the Bural-Sardyk deposit is located. The early views on this deposit of high-quality siliceous raw materials have been amended using the new data. This deposit is associated with quartzites of the Meso-Proterozoic Irkut formation and discordantly overlaps the Gargan block. According to the detailed study results on the cover of the Oka-Urik interfluve area, its structure is predetermined by physical and mechanical properties of the rocks, and the degree of rock dislocation depends on the rock viscosity. Most of its section is composed of viscous quartzites that create the structural framework of the study area. Such viscous rocks are not prone to folding. An alternative is detachment taking place concordantly to layering. The only interlayer is composed of limestones that underwent intense plastic deformation reflected in multi-folding. Actually, limestones mark a zone of plastic detachment. The authors propose an interpretation of the formation of the deposit structure. The main deformation event was preceded by the sediment transformation stage in conditions of diagenesis and catagenesis due to the influence of a lithostatic load. Primary recrystallization under lithogenesis led to the formation of high-purity silicon rocks. At the next stage, the rocks were subjected to longitudinal compression in the PT conditions of green-shale metamorphism. This stage is mainly evidenced by sublayer detachments. In parallel with that process, quartzites experienced super-plastic flow and recrystallization, which led to the formation of super-quartzites. The bodies of super-quartzites tend to be layered and less discordant. Such a structural position suggests the possibility of detecting latent manifestations of super-quartzites at different levels in the quartzites of the Irkut formation. Tectonic detachments are observed in the sedimentary cover and do not reach the foundation. Based on these features, there are reasons to use the thin-skinned tectonic model. Rock deformation occurred under stress oriented from the northwest to the southeast. This is indicated by the position of the axial surfaces of the folds, as well as the orientations of the maximum compression axis and the crystallographic axes of quartz. Macro- and microstructural data indicate that the tectonic transport of matter was directed to the southeast. The research results were used for compiling a new geological map of the deposit.

We present results of lithogeochemical, diatomic and palynological studies of sediments from the Tunka-13 well that was drilled in the southeastern part of dry Tunka basin in the Baikal rift zone. At the base of the section, there is an eroded basaltic flow of 16–15 Ma. From lithogeochemical signatures, we identify nine sedimentary units. The seven lower ones (interval 7.2–86.5 m) belong to the Tankhoi formation, the eighth (interval 2.7–6.6 m) to the Anosov formation, the ninth (interval <2.4 m) to the sandy stratum. We determined local sources of clastic material of basaltic and silicic compositions for units 1 and 2, respectively, and remote sources of silicic compositions for the overlaying units. The section shows a change from alluvial facies (units 1–3) through avandelta (unit 4) and lacustrine ones (units 5–7), again to alluvial facies (unit 8) and then to lacustrine-eolian ones (unit 9). Spore and pollen spectra from sediments of units 1–7 are divided into three palynozones (PZ), reflecting the vegetation change in the Late Miocene – Early Pliocene: PZ-1 – coniferous and deciduous forests with a small participation of thermophilic broadleaved species in moderately warm, humid climatic conditions; PZ-2 – enhancing the role of hemlock and more diverse thermophilic deciduous rocks in more humid and warm conditions; PZ-3 – a gradual reduction in the number of hemlock and other dark coniferous species, removing broad-leaved species by birch and alder, growing grassy communities in wetlands due to climate cooling. We identified layers of lacustrine facies by occurrence of fossil diatoms that are absent in the layers of the alluvial and avandelta facies. In lacustrine sediments, we distinguish four diatom zones: DZ-1 denotes a relatively deep Late Miocene paleolake, marked by planktonic species, DZ-2, DZ-3 and DZ-4 – a shallow Early Pliocene lake with a developed littoral zone and short transgression. The Late-Miocene paleolake transgression, indicated by changing facies, is associated with structural reorganization, accompanied by volcanic extinction in the Tunka valley about 9–8 Ma, and the Early Pliocene short transgression with a new reorganization, reflected in volcanic rejuvenation about 4.0 Ma.

The study is focused on micrometeorites from bottom sediments sampled from the Selenga-Buguldeika lintel of Lake Baikal. Their diatom analysis showed continuous sedimentation during the Holocene. Mineralogical analysis identified a complex of minerals, including micrometeorites, which amount to 0.6 % of the heavy fraction weight. A detailed study of the micrometeorites was carried out using a JXA8200 electron probe x-ray microanalyzer. It was established that their chemical composition is predominantly represented by Fe, O, C, and Zn, i.e. these are type 1 α-micrometeorites. Based on the difference in the chemical composition of the micrometeorites in the sedimentary strata section, it is proposed to refer to such micrometeorites not only for stratigraphic correlations, but also for impact stratigraphy schemes.

The first geochronological data have been obtained for Amnunakta massif composed of monzogabbro-monzodiorite and located in the southeastern part of the Selenga-Stanovoy superterrane. It was found that the age of Amnunakta massif (240 ± 1 Ma) is almost similar to that of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex, which were sampled from the eastern flank of the Selenga-Vitim Volcano-Plutonic belt. Taking into account the geological position and geochemical features of the Amnunakta massif, there are grounds to suggest that the formation of this massif (as well as of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex) was associated with one of the impulses of bimodal intraplate magmatism during the evolution of the Selenga-Vitim belt.

Seismicity, heat flow, seismic tomography data, prerift and synrift magmatism are considered as intensity indicators of geodynamic processes along the Atlantic-Arctic rift system (AARS). In this rift system, several large (over 100 km ) sub-latitudinal displacements of the rift axis are due to left-lateral strike-slip faulting. The AARS segments are distinguished by the age of splitting of continental plates from each other. A dependence is revealed between the current thermal state of the mantle under the AARS and the age of spreading start. This dependence is established from both seismic tomography and heat flow data. In section δ(Vp/Vs), the locations of the main segmenting faults and ‘cold’ anomalies in the upper mantle are coincident. Distributions of total seismic moments are practically synchronous in the depth intervals of 0–13, 13–35, and >35 km. The maximum values above the plumes are represented by higher seismic moments in the surface layer. The main demarcation zones differ in maximum energy release values in the AARS with shearing features. Comparison of these values against the age of the start of spreading processes shows trends of heat flow and medium field tomography in the AARS segments. The trends confirm the thermal interpretation of the seismic tomography data and suggest mantle cooling with age and a decrease in the mean temperatures of the mantle. The main factor causing the sublatitudinal asymmetry of heat flow in the AARS is the impact of Coriolis forces on the magma in the asthenospheric source. Most of the synrift igneous formations seem to be related to the influence of long-lived anomalies in the mantle, which had lower rates of magma generation than those typical of the formation of magmatic provinces. In conditions for spreading and the formation of the oceanic crust, the process followed the principle of energy cost minimization, and the prerift magmatic provinces with the pre-processed crust contributed to the choice and positioning of the AARS trajectory. The plume branches are imposed in the tomographic section and thus ‘concealing’ the relationship between the age and the thermal state. However, that does not change the trend to cooling of the mantle beneath the AARS, proportionally to the time since the start of spreading.

Seismotectonic deformations in the Middle America Trench and their features in the area of preparation of the Chiapas earthquake, М_W=8.2, 08 September 2017, were determined using the data on 2244 focal mechanisms of earthquakes for the period of 1977–2017. The distribution of seismicity with depth was studied in detail. The decrease in the depth of the Benioff zone in the north-western subduction segments and the increase in the south-eastern segments is associated with the age of the subducting parts of the Cocos plate and the angle of their immersion. The latter mechanism can also explain the presence of earthquakes with normal focal mechanism on the oceanic uplift in the south-eastern segments of the subduction zone and their absence in the north-western ones. In general, the typical character of subduction deformations has a number of features in the Middle America Trench. The predominance of shortening by horizontal components and elongation by vertical ones at depths up to 35 km is replaced by the transitional type with mosaic distribution of deformations of different signs in the depth range of 36–70 km. Even lower, in the depth range of 70–105 km, the type of deformation changes to the opposite with respect to the upper horizon. The Chiapas earthquake occurred on the border of regions with different types of deformation, which indicates softening of the block’s medium to the west of the hypocenter and its hardening to the east. Such a state of the lithospheric medium may indicate the presence of a deformation shadow zone in the Chiapas earthquake preparation area.

Ample geologic and geophysical data provide the basis for distinguishing the 102–104° E geodivider in the North, Central and South Asia. The geodivider’s central part is confirmed by the data on seismicity, seismically active faults and the modern crust block structure. These data and historical and instrumentally identified earthquake epicenters were used for a more correct definition of the block boundaries and interblock zones in the central part of the geodivider and in its wings. Seismic energy is considerably increased (to 10¹¹–10¹⁶ J) in the eastern part of the geodivider’s western wing, and rarely increased directly in the geodivider itself. Near the geodivider, a seismic energy increase is detected east of it only at the western border of the South-Eastern China Block. The authors analyzed deep seismic sections and constructed energy dissipation graphs along transects crossing the geodivider and its western wing. The analysis and the graphs show the predomination of left-lateral NW-striking slips in the north, thrusts to the east and southeast in the center, and right-lateral NE-striking slips in the south. The total seismic energy increases constantly to the west. In the central and northern segments of the geodivider’s central part and west of it, horizontal blocks displacements cause a direct influence on seismicity level increasing and changes in geodynamic regimes within the investigated territory of Central Asia. Changes in the horizontal displacement vector are accompanied by the change of tectonic strain regimes. Increased heat flow values to the east from the geodivider within the East Asian transit zone are probably related to the change of the geodynamic regimes in the same direction under the influence of the submerged Pacific slab. The data obtained by the Chinese and Russian researchers confirm delamination (stratification) processes in the Southeast Tibet crust during its interaction with the colder and thicker lithosphere of Southeast China, and displacement of its upper layers to the southeast and south, as we supposed in our earlier publications.

The RAS Research Station started geodynamical research at the Bishkek Geodynamic Test Area (BGTA) in 1980s. This test area is located in the Northern Tien Shan, one of most seismically active zones of Central Asia. The distribution patterns of crustal deformation in space and time are investigated by a complex of geophysical, seismological and geodesic methods. Long-offset transient electromagnetic (LOTEM) technique is an important component of the geophysical research carried out at BGTA with the focus on forecasting of seismic activity dynamics. LOTEM is considered to be one of the most informative methods for obtaining data on multilayered conductive anisotropic geologic environment. This article presents the results of integrated interpretation of LOTEM sounding data recorded at permanent electro-magnetic monitoring stations, Ak-Suu and Shavai. The time series of specific electrical resistance are analyzed to reveal a correlation with the stress-strain state of the geologic environment and seismic process in the study region in the period from January 2016 to October 2018. It is established that the deformation process taking place at a depth of more than 8.0 km is reflected in the time series of specific electrical resistance in the form of bay-shaped negative variations. A decrease of apparent resistance is observed when the receiver dipoles of the measurement unit are arranged in the meridian (N-S) direction. The periods of compression in the submeridional direction coincide with the periods with the highest density of seismic events. A comparison of earthquake hypocenter locations against the topographic relief and the data on regional faults shows the maximum density of hypocenters at the axial parts of Northern Tien Shan ridges.

The paper presents the results of the study aimed at predicting velocities of modern vertical movements of the Earth’s crust, which used the approach developed by Professor G.I. Karataev. This approach is based on mathematical simulation of geological and geophysical phenomena and an axiomatic correlation model for predicting various parameters of the crust from the data on gravitational anomalies. We pioneer in using this approach to study the territory of Belarus on the basis of geodetic, geological, geophysical and seismological data, as well as modern models showing gravitational fields and topography. This paper presents regression equations between the modern vertical movement velocities, gravitational and magnetic fields, crust thickness, and topography data. These equations give reasonably accurate data for constructing a map of forecasted modern vertical movement velocities for the territory of Belarus. Our map proves that the approach based on a correlation model and a complex of geodetic, geological, geophysical and seismological data for predicting the modern vertical movement velocities is very promising and capable of improving the reliability of forecast mapping. It should be noted that other maps of modern vertical crustal movement velocities for territories, including the geostructural elements of different ages and different types, were constructed using the method of simple linear interpolation, which is highly likely to cause prediction errors. In such case, prediction of modern vertical crustal movement velocities should be based on established patterns and correlations between the crustal movements, geophysical fields, and development history of geological structures and their elements.

Physicochemical interactions in the water – porphyrite system in conditions of formation of nitrogen-rich hot springs were studied using computer simulation. Compositions of model solutions during such interactions are determined by a combined influence of the compositions of primary and secondary rock minerals. In the investigated interaction range, the solution actively processes large quantities of the primary rock in favor of secondary minerals, while dissolved components are accumulated in small amounts in the solution itself, and therefore the salinity is low. The intervals of the formation of hydrosilicate, bicarbonate and sulfate sodium solutions are clearly distinguished in the process of irreversible hydrolytic transformation of porphyrite. In a certain range of interactions, the compositions of the model solutions are well comparable with the compositions of natural high-fluoride hot springs. Nitrogen-rich hot springs are strongly influenced by meteogenic factors detectable by detailed and/or sufficiently long-term observations. In deep and surface conditions, the model solutions and natural hot springs considerably differ in composition. Differences are hardly noticeable in the behavior of cations, fluorine, chlorine, and sulfates, but are strongly manifested in changes in the quantities of carbon and silicon compounds and transformations of their forms. These transformations explain the hitherto incomprehensibly different ratios of hydrocarbonate and carbonate ions and hydrosilicate ions and silicic acid both in different hydrothermal sources and in different analyses of hot springs in nature. The development of thermal waters in crystalline rocks is related to two types of heterogeneities that are typical for the development of geological bodies. The first heterogeneity is the disturbed continuity of rocks in fault zones of various orders, due to which groundwater can penetrate into these structures. The uneven distribution of anionic elements in space is another heterogeneity predetermining the groundwater composition and, in particular, accumulation of fluorine, which is confirmed by the results of geological studies, as well as the study of the formation of high-fluoride groundwaters (including thermal water) in various geological structures.

The study is focused on thermochemical mantle plumes with intermediate thermal power (1.15 < Ka < 1.9). Previously we have shown that these plumes are diamondiferous. Based on the laboratory modeling data, the flow structure of a melt in a plume conduit is represented. A plume melts out and ascends from the core – mantle boundary to the bottom of the continental lithosphere. The plume roof moves upwards in the lithosphere because of melting of the lithospheric matter at the plume roof and due to the effect of superlithostatic pressure on the roof, which causes motion in the lithosphere block above the plume roof. The latter manifests itself by uplifting of the ground surface above the plume. As the plume ascends through the lithosphere, the elevation of the surface increases until the plume ascends to critical level xкр, where an eruption conduit is formed. In our model, plume ascent velocity uпл is the rate of melting at the plume roof. Values of uпл and the ascent velocity of a spherical plume roof due to superlithostatic pressure U are calculated. Relationships are found between these velocities and the plume roof depth. The dependence of the velocity of the surface’s rise on the dynamic viscosity of the lithosphere block above the plume is obtained. A relationship is determined between the maximum surface elevation and the lithosphere viscosity. The elevation values are determined for different times and different lithosphere viscosities.

The results of laboratory modeling of flow structure at the plume conduit/eruption conduit interface are presented. The flow was photographed (1) in the plane passing through the axes of the plume conduit and the eruption conduit; and (2) in case of the line-focus beam perpendicular to the axial plane. The photographs were used for measuring the flow velocities in the plume conduit and the eruption conduit. Corresponding Reynolds numbers and flow regimes are determined. The relation of dynamic pressure in the eruption conduit to that in the plume conduit is found for intermediate-power plumes. The melt flow velocity in the eruption conduit depends on superlithostatic pressure on the plume roof, plume diameter and kinematic viscosity of the melt. Its values are determined for different kinematic viscosities of melt.

According to the steady state of fault and energy balance, we provided a new idea to observe the precursors for a stressed fault. The meta-instability (or sub-instability) state of a fault is defined as the transition phase from peak stress to critical stress of fast instability (earthquake generation) during a full period of slow loading and fast unloading. The accumulative deformation energy begins to release in this stage. Identifying its deformation before fast instability would be beneficial to obtain premonitory information, and to evaluate the seismic risks of tectonic regions. In this study, we emphasized to analyze deformation process of the meta-instable stage with stain tensor data from a straight precut fault in granite at a slow loading rate, and observed the tempo-spatial features during the full deformation process of the fault. Two types of tectonic zones and instabilities occur on the stick-slip fault. The low- and high-value segments in the volume strain component appear along the fault strike with a load increment. The former first weakens and then becomes initial energy release segments; the latter forms strong stress-interlocking areas and finally turns into the initial region of fast instability. And there are two stages in the entire instable process of the fault: the initial stage is associated with the release of the low volume strain segments, which means fault pre-slips, slow earthquakes or weak earthquakes. The second one characterizes a strong earthquake through the release of high volume strain parts. The rupture acceleration in the first stage promotes the generation of the second. Moreover, fault instability contains two types of strain adjustments along the fault: the front-like strain change along the transition segments from low- to high- strain portions with volume strain release, and the compressive strain pulse of fault instability after the volume strain release extends to a certain range with loading increment. In laboratory experiments, the front-type strain occurs about 12 seconds before fast fault instability; the compressive pulse initiates within less than 0.1 second, and then the fault turns quickly into a dynamic strain adjustment, which appears quasi-synchronously between different measurement points, and, finally, an earthquake is generated.

The complex of geophysical methods was successfully applied in the Alakit-Markha kimberlite field of the Yakutsk diamondiferous province. A pipe was identified in the local forecast area specified within the field at the previous stage of prospecting. The studies using electric tomography (ET), radon survey (RS) and microseismic sounding (MS) covered an area of ≈1000⨯500 m. Based on the jointly processed ET and RS plan images and MS profiles, a tubular body was detected in the sedimentary cover. It is confined to a fault node and stands out among the host rocks by low electrical resistivity, increased soil radon concentrations and high spectral ratios of the horizontal and vertical components of microseisms. Its complex shape is manifested at the ground surface by two isometric structures (each being several hundred meters long), which jointly form a dike-like body at a depth of ≈40 m, as shown by the electrical tomography images. According to the MS data, its root part is detected to comprise one or two fractured narrow zones that are traceable to a depth of 2 km and below. The structure of the identified body and its chemical composition will be determined after exploratory drilling is complete. Today there are grounds to conclude that using ET, RS and MS methods jointly as a complex described in the article proved effective for identifying pipes controlled by fault zones in the sedimentary cover areas.