The TerraneChrone^® (LA-ICP-MS) technique has been applied to carry out an integrated study of detrital zircons in sandstones sampled from the basal horizons of the stratotypical Riphean sequence in the Southern Urals, specifically the Navysh and Chudin suites of the Ai Formation of the Burzyan Group in the Bashkir Uplift. The concentrations of trace elements in the detrital zircons suggest that the role of oceanic or marginal-marine complexes among the primary sources of zircons was insignificant, and show a better agreement with the intra-continental rather than passive-margin origin of the Riphean basin, whose basal levels are composed by the Ai Formation. The U/Pb ages of zircons from samples K13-206 and M08-16-1 are generally similar: the Paleoproterozoic zircons predominate (the dominant peaks are actually coincident, 2063 and 2055 Ma), and only a few grains of the Archean age are present. Despite the similar U/Pb ages of the detrital zircons, these two samples considerably differ in their Hf isotopic features and the concentrations of trace elements, which means that the zircons in the studied sandstones are of different geodynamic origin. The characteristics of these zircons can be explained by a model showing the Ai Formation in the Navysh graben that is a rift structure and a predecessor of the Kama-Belaya aulacogene in the inner Volga-Ural region of the Paleoproterozoic supercontinent Columbia. At the initial stage of rifting, the granitoid complexes with a lower total silicic acidity, which composed the graben walls, had been eroded; as a result of erosion, coarse clastic rocks accumulated within the Navysh graben and formed the Navysh suite. A specific “carbonatitic” complex containing zircons (about 2.0, 2.5, 2.85 and 3.6 Ga) and the Palaeoarchean crustal material in the substrate of their parent rocks was also eroded. In the final stage of rifting, already at the initial stages of the development of the Kama-Belaya aulacogen (Chudin suite), the erosion products from the paleo-aquifers occupying vast areas began to be transported into the rift. The primary sources of clastics for the Chudin suite were both granitoids of the lower and normal silicic acidity. Besides, a specific “carbonatitic” complex containing juvenile zircons (about 2.05 Ga) was eroded. However, by that time, significant areas of the Archaean basement of the Volga-Ural region might have become hidden underneath a proto-cover and thus not eroded, so the Archean detritus in the Chudin suite is poorly represented in comparison with the Navysh suite, considering both the amounts and ages of detrital zircons. As of today, the Precambrian carbonatite rocks within both the Taratash complex (composing the basement of the Navysh graben) and the southeastern segment of the East-European Platform have not yet been described. The source of the “carbonatite” zircons remains unknown and can be discovered as more and more data on the basement rocks is accumulated.

Ancient primary boninitic melts of the Gorny Altai (65–105 km, 1410–1590 °C) were studied from the composition of melt inclusions in clinopyroxenes. We estimated their parameters and the conditions for the onset of magma crystallization in an intermediate chamber at a depth of about 30–35 km, which appear similar to the reference boninitic magmatism of the modern Izu-Bonin island arc. A combined analysis of the composition of inclusions and clinopyroxenes from Gorny Altai boninites shows that within a range of minimum temperature values (1140–1120 °C), the crystallizing material continuously ascends from a depth of 12 to 0.6 km. The pattern is different in case of higher-temperature magmas, and three zones of pyroxene crystallization are distinguished: 18.0–13.8 km (1245–1205 °С), 12.0–3.5 km (1240–1185 °С), and 3.3–0.6 km (1185–1145 °С). Actually, these zones correspond to the intermediate deep-seated magmatic chambers typical of modern island-arc subduction zones [Dobretsov et al., 2016]. Based on the detailed study of zonal phenocrysts of clinopyroxene in boninites from the Kuray ophiolites, we established the parameters of the evolution of the ascending boninite melts. Three temperature intervals (1220–1200 °С, 1235–1210 °С, and 1120–1220 °С) and three pressure ranges (1.5–11.5 kbar, 2.0–6.0 kbar, and 2.0–0.3 kbar) are distinguished. One case shows a significant pressure drop (from 11.5 to 1.5 kbar) with a small drop in temperature (from 1220 °C to 1200 °C). In the second case, the pressure rises from 2.0 to 6.0 kbar, and the crystallization temperature decreases from 1235 to 1210°C. In the third case, crystallization begins at a stable temperature (1120–1140 °C) and a stable pressure (1.4–2.0 kbar); then, in the near-surface conditions, the temperature increases to 1220 °C, and the pressure decreases sharply to 0.3 kbar.

From the early 1980s, the data on the bulk chemical composition of sandstones and mudstones are actively involved for interpretation of the paleogeodynamic settings for sedimentary sequences. Discriminant diagrams such as K₂O/Na₂O–SiO₂/Al₂O₃ [Maynard et al., 1982], (Fe₂O₃*+MgO)–K₂O/Na₂O and others [Bhatia, 1983], SiO₂–K₂O/Na₂O [Roser, Korsch, 1986], (K₂O+Na₂O)–SiO₂/20–(TiO₂+Fe₂O₃+MgO) [Kroonenberg, 1994] etc., are now widely used in regional investigations to classify terrigenous rocks from several paleogeodynamic settings (passive and active continental margins, oceanic and continental volcanic arcs etc.) with a certain ‘percentage of consistency’. The first diagrams DF1–DF2 for syn-rift compositions were published in the early 2010s [Verma, Armstrong-Altrin, 2013]. This article analyzes the bulk chemical compositions of syn-rift sandstones from intracratonic rifts and rifts formed during the break-up of the Columbia and Gondwana supercontinents, rifts within volcanic arcs and related to the collapse of collision orogens (for example, Permian sandstones of the Malužiná formation, Western Carpathians, Slovakia). Our database includes the Neoproterozoic Uinta Mountain Group (USA), the Cretaceous Omdurman formation of the Khartoum Basin (Sudan), the siliciclastic deposits of the Kalahari Basin (East African rift zone), the sandstones of the Vindhyan Supergroup (India), the Neoproterozoic Ui Group of the Uchur-Maya region (Southeast Siberia), the Meso-Neoproterozoic Banxi Group (Southern China), the Mesoproterozoic Belt-Purcell Supergroup (USA), the Oronto and Bayfield Groups of the Midcontinent (USA), as well as the sandstones of the Upper Precambrian Ai and Mashak formations, and the metasedimentary rocks of the Arsha Group (Southern Urals). The article examines: (1) the position of the syn-rift sandstone compositions (fields) on the log(SiO₂/Al₂O₃)–log(Na₂O/K₂O) classification diagram and the F1–F2 diagram, which gives the possible composition of the catchment areas rocks; (2) the position of the syn-rift sandstone compositions, as well as the average values of various indicator ratios and discriminant functions, in the K₂O/Na₂O–SiO₂/Al₂O₃, F3–F4, SiO₂–K₂O/Na₂O and DF1–DF2 diagrams. The analysis of the results shows that the fields of the syn-rift sandstones are characterized by a wide dispersion of log(SiO₂/Al₂O₃) (0.4…3.5) and log(Na₂O/K₂O) values (~0.2…6.0 and more). A number of the values do not fit into the typical areas on the classification diagram of F.J. Pettijohn et al., which suggests that the syn-rift sandstones vary considerably in composition that is controlled by a significant number of factors. The diagram of J. Maynard et al. is not suitable for assigning certain sandstone associations to the ‘syn-rift sandstones’ category. In the diagrams of M. Bhatia and K. Crook, as well as those of B. Roser and R. Korsch, the fields and mean points of the syn-rift sandstones are mainly located in the area of passive continental margins; thus, these diagrams can not be used to classify the syn-rift sandstone associations. Contrariwise, on the high-silica DF1–DF2 diagram [Verma, Armstrong-Altrin, 2013], ~80 % of the objects from our database are localized in the field of syn-rift compositions and show a good correlation with the ‘percentage of consistency’ evaluated by the authors for the samples from similar settings (79–85 %). Thus, according to the data presented in the article, the DF1–DF2 diagram is the most rational and acceptable discriminant diagram for assigning certain sandstone associations to the ‘syn-rift infilling’ category.

Recently, a unique geophysical polygon has been created on the Taimyr Peninsula and the adjacent territories. Its densely spaced set of seismic and electric prospecting profiles makes it possible to investigate the structure of the continental lithosphere to the depths of 50–60 km (Fig. 1). The sedimentary cover and the deep horizons of the crust and upper mantle are studied in detail to discover new facts in the history of the geological development of the northern Siberian platform. The contrasting anomalies recorded at the lower crust levels give evidence of considerable changes in density and electrical conductivity, which coincide in plan with the most significant geological structures in the northern regions of Central and West Siberia (Fig. 2). The relationships of the largest uplifts and troughs with the decomposition and compacting processes at the level of Moho are indicative of, on the one hand, the metamorphism occurring under the influence of asthenospheric fluids, and, on the other, the determining role of lithostatic pressure equalization in the formation of these structures. Thus, for the first time, the direct geophysical surveys have shown that the nature of tectonic processes is not limited to only simple horizontal movements of the cratons and associated deformation. Our data shows that the deep geological structure of the study area can be explained, in addition to collision, by the vertical stresses associated with the compaction/decompaction of the crust under the influence of the materials uplifted from the mantle and the lithostatic pressure equalization compensating for the density changes. The vertical tectonic movements are not unidirectional and periodically change their sign, as evidenced by the inversion nature of the largest structures of the sedimentary cover in the Taimyr Peninsula (Fig. 3). In the course of the geological development, the troughs are generally replaced by banks, and uplifts and ridges are involved in subduction, to varying degrees. According to the data obtained, such changes are determined by the differences in the depth levels of the large blocks of the lower crust and upper mantle. These variations seem to play a significant role on other continents; in that regard, their further studies will contribute to a better understanding of global geodynamics.

In the regions of high seismic activity, investigations of fault zones are of paramount importance as such zones can generate seismicity. A top task in the regional studies is determining the rates of activity from the data obtained by geoelectrical methods, especially considering the data on the faults covered by sediments. From a practical standpoint, the results of these studies are important for seismic zoning and forecasting of natural and anthropogenic geodynamic phenomena that may potentially occur in the populated areas and zones allocated for construction of industrial and civil objects, pipelines, roads, bridges, etc. Seismic activity in Gorny Altai is regularly monitored after the destructive 2003 Chuya earthquake (M=7.3) by the non-stationary electromagnetic sounding with galvanic and inductive sources of three modifications. From the long-term measurements that started in 2007 and continue in the present, electrical resistivity and electrical anisotropy are determined. Our study aimed to estimate the variations of these electrophysical parameters in the zone influenced by the fault, consider the intensity of the variations in comparison with seismicity indicators, and attempt at determining the degree of activity of the faults. Based on the results of our research, we propose a technique for measuring and interpreting the data sets obtained by a complex of non-stationary sounding modifications. The technique ensures a more precise evaluation of the electrophysical parameters. It is concluded that the electric anisotropy coefficient can be effectively used to characterize the current seismicity, and its maximum variations, being observed in the zone influenced by the fault, are characteristic of the fault activity. The use of two electrophysical parameters enhances the informativeness of the study.

The original continental crust of the deep-sea basins in the Sea of Okhotsk region was considerably reworked by tectonic and magmatic processes, whereby it has become substantially denser while less thick. The subcrustal lithospheric mantle of the South Okhotsk basin is characterized by the high velocities of longitudinal seismic waves (8.4 km/s) and higher density values, accordingly. A poly-astenospheric model is proposed for the South Okhotsk deep-water basin: it comprises three asthenospheric layers separated by hardened layers. The roof of the upper mantle asthenosphere in the basins is observed at shallow depths (70–75 km), showing low electrical resistivity (r=3–10 Om×m). The asthenospheric layers contain the substantial amounts of magmatic melts (11–16 %), which significantly reduce their viscosity. Emplacement of basic-ultrabasic melts in the Earth's crust and subcrustal lithospheric mantle (i.e. dense mass redistribution, and consolidation of the crust and mantle), as well as the lower viscosity asthenospheric layers facilitate the isostatic subsidence during the formation of deep-sea basins. The deep structure of the continental Pannonian basin, characterized by a high heat flow, is compared to the deep structure of the neotectonic deep-water depression in the Sea of Okhotsk region.

Earthquakes can generate thermal anomalies in the atmosphere at low altitudes. Pending well-focused detailed studies, such phenomenon may be referred to as a precursor for earthquake prediction. However, today the pre-earthquake thermal anomalies are not clear enough. In this paper, the thermal anomalies prior to the April 25, 2015 Mw 7.8 Gorkha (Nepal) earthquake are investigated from the Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST), air temperature and Outgoing Longwave Radiations (OLR) data. The 2D and 3D wavelet transformation techniques are used to interpret the real time enhancement of the daily MODIS and OLR data before the impending earthquake. Using the wavelet density spectrum, pre-earthquake anomalies in MODIS and OLR are found in connection to the impending earthquake. The spatial images of MODIS and OLR show the evolutionary pattern of the emanation of ions from the epicenter and the surrounding area. The most important feature revealed by the spatial analysis is the eastward migration of temperature clouds due to a strong electric field. The satellite based LST data showed deviation, which crosses the upper bound by 5 °C. All the observations in our case study strongly support the notion of pre-earthquake thermal anomalies. Based on the analysis of the results, it can be concluded that the overabundance of ions from the seismogenic zone is responsible for prompting large temperature perturbations in atmospheric layers.

The properties of slow seismic activity migration have been revealed by the space-time analysis of the total earthquake energy (LgE_sum). Our study of seismic activity covers the fragments of  the Central Asian, Pacific and Alpine seismic belts: the Baikal rift system (BRS, Russia), the San Andreas fault zone (California, USA), the Christchurch fault (New Zealand), the North and East Anatolian faults (Turkey), the Philippine subduction zone, and the central fragment of the Mid-Atlantic oceanic ridge. The chains of LgE_sum clusters mark the propagation of the maximum stresses front in the weaker crust areas, the zones of fault dynamic influence, and the regions of conjugated tectonic structures. The migration process is characterized by a periodicity, changes in direction, and similar modular values of the migration rates within a single fault segment (or a fault zone), which is probably related to the mechanical and rheological crust and upper mantle properties. The data analysis shows that a strong earthquake source may occur at a location wherein the front of seismic activity propagates with periodical changes in direction, and such a source can develop within a period that is multiple of the migration fluctuations, probably associated with the influence of external periodic factors. The main periods of migration fluctuations (2–4 years, and 9–13 years, in different ratios) are present in the seismic regimes of different seismic belts. The migration rate, as well as the propagation velocity of the maximum stresses front, directly depends on the velocity of movements between the plates in the region.

In connection with changes in the stress-strain state of the Earth's crust, various physical and mechanical processes, including destruction, take place in the rocks and are accompanied by tectonic earthquakes. Different models have been proposed to describe earthquake preparation and occurrence, depending on the mechanisms and the rates of geodynamic processes. One of the models considers crustal stretching that is characteristic of formation of rift structures. The model uses the data on rock samples that are stretched until destruction in a special laboratory installation. Based on the laboratory modeling, it is established that the samples are destroyed in stages that are interpreted as stages of preparation and occurrence of an earthquake source. The preparation stage of underground tremors is generally manifested by a variety of temporal (long-, medium- and short-term) precursors. The main shortcoming of micro-modeling is that, considering small sizes of the investigated samples, it is impossible to reveal a link between the plastic extension of rocks (taking place in the earthquake hypocenter) and the rock rupture. Plasticity is the ability of certain rocks to change shape and size irreversibly, while the rock continuity is maintained, in response to applied external forces. In order to take into account the effect of plastic deformation of rocks on earthquake preparation and occurrence, we propose not to refer to the diagrams showing stretching of the rock samples, but use a typical diagram of metal stretching, which can be obtained when testing a metal rod for breakage (Fig. 1). The diagram of metal stretching as a function of the relative elongation (to some degree of approximation and taking into account the coefficient of plasticity) can be considered as a model of preparation and occurrence of an earthquake source in case of rifting. The energy released in the period immediately preceding the earthquake contributes to the emergence of its precursors. This article discusses various earthquake precursors with reference to the energy model of tectonic earthquake preparation and occurrence in conditions of crustal stretching.

The measurement data on the Kamchatka Canyon, including the block diagram, a set of echograms, the longitudinal profile of the canyon, and the bathymetric map, and the continuous seismoacoustic profiling data (CSP) has been reinterpreted. The study covers the shelf and the upper and middle parts of the continental slope. Regional gas-saturated strata have been discovered in the Cenozoic cover of the shelf and the continental slope, as well as in the block landslides of the sedimentary cover on the left (~55 km long, the western slope of the Kamchatka Cape) and right (more than 25 km long, the Kamchatka river delta front) sides of the canyon. Hanging landslides on the left side are associated with a 100–150 m increase in the depth of the canyon. On the middle slope, there is a large (28 km long) block landslide and its almost compensated paleochannel. The sub-latitudinal turn and the displacement of the canyon mouth to the north by 70 km is related to uplifting of the ridge-barrier in the Middle Pleistocene – Holocene. Based on the measurement and CSP data, it becomes possible to contour landslides on the sides of the Kamchatka Canyon, select the most hazardous locations (hanging landslides on the upper slope) for numerical modeling of potential landslide-related tsunami, and develop recommendations pertaining to construction of a new international sea port in the town of Ust-Kamchatsk.

The article presents the detailed analysis results considering bottom sediments from the Chukchi Sea. Two core samples, b16 and НС–8 were taken from the northern Herald Canyon 150 km northeast from NE Wrangel Island. Core b16 has been studied in more detail. According to the ²¹⁰Pb measurements, the recent sedimentation rate amounts to 0.9 mm/y^–1 at the sampling point. In the bottom layer of the core sample, the minimum concentrations of biogenic components (SiO_2bio, C_org, N_tot, and Br) and the increased concentrations of cold-water diatom species Thalassiosira antarctica may result from low biological productivity during the Maunder Minimum. A correlation with recent global warming (11–22 years) is shown by the increased concentrations of SiO_2bio, C_org, N_tot, and Br and the decreased values of magnetic susceptibility and X-ray density in the top layer (1–2 cm) of the same core sample. The results of our geochemical and diatom analysis support the available literature data and confirm that the Late Holocene sedimentation in the Chukchi Sea takes place in the zone wherein the water transits from the Pacific to the Arctic Ocean.

The article describes the complex hydrogeological conditions of the Baikal rift zone viewed as a large structural element and pioneers in distinguishing two independent hydraulic systems in the study area. Groundwater resources and compositions of groundwater in these two systems are generated in fundamentally different ways. In the deep sediment layers, groundwater generated due to sedimentation is at the stage of elision (exfiltration) water exchange. Active phase transition of clay minerals to hydromica causes an additional water release, and sedimentary water and regenerated groundwater infiltrate from the condensed clay strata to sandy horizons. This process is accompanied by decompaction, heaving sand, and high (extra-high) reservoir pressures. Nitrogen-rich water and carbonic thermal water associated with faults and fault nodes are widespread in the basement of the Tunka depression. The thermal water result from infiltration and, together with fresh water, represents a uniform hydraulic system. Its development is determined by the dynamics of infiltration water in the water-feeding area in the Tunka loaches. At different hypsometric levels of the hydrogeological section, nitrogen-rich water descends, while carbonic thermal water ascends, and these processes occur simultaneously. Our study is focused on the physicochemical processes of the interaction between groundwater and sedimentary and crystalline rocks. It shows that the ion-salt and gas compositions of not only nitrogen-rich thermal water, but also those of methane water and carbonic thermal water occur in the ‘water-rock’ system without involving any additional substance from external sources. Compared to other thermal water, the composition of carbonic water is formed in a more complex way: first, it goes through the stage of the nitrogen-rich thermal water while passing through the aluminosilicate rocks and only then interacts with the carbonate rocks and become carbonic. The formation of carbonic water is accompanied by intensive karst processes at depths, which are ceasing closer to the surface. As a result of degassing, an opposite process is activated: authigenic minerals and travertines are formed on the surface. Groundwater and its gas phase are involved in the formation of rocks with a negative temperature, which are abundant in the Tunka depression, as well as large positive forms of the relief. It is shown that the activity of groundwater is not limited to the role of a filler in the host rocks and an intermediary medium between different geospheres. Groundwater is an active agent that initiates, controls and implements many geological processes.

In our study, high-resolution digital elevation models (HRDEM) were generated by combining the data from airborne laser scanning (ALS, 2012) and long-range terrestrial laser scanning (TLS, 2015) and used for qualitative and quantitative analysis of recent morphodynamic processes in the Vistula river bed near Nieszawa, Central Poland. The study area was a river stretch nearly 1 km long, in its lowland part, with the 440 m wide channel and 3.5‑5.0 m high banks. It is located 27 km downstream from the reservoir in Włocławek, so it is under the influence of the reservoir. The TLS measurements were performed from the opposite bank of the river, from a distance of up to 750 m. By combining the ALS and TLS data, we investigated and evaluated both the horizontal variations in the height of the river bank and changes in its profile, with a high resolution of about 900 points/m². Our results show that in this river stretch, both the transverse profile of the river bank and the location of its upper edge have been changed during the three years between the ALS and TLS measurement sessions. The scale of this phenomenon varies from a complete lack of erosion to lowering of the upper edge of the cliff by about 1 m, in some points even up to 2 m. The applied methods allowed us to estimate the area of the observed transformations, in contrast to the conventional methods that enable only analyses in selected transverse sections.

The model of a thermochemical mantle plume is described. The scheme of origination of the plume from the core-mantle boundary is presented. The basic ratios for determining the thermal power and the diameters of thermochemical plumes are given. After eruption of the melt from the plume conduit to the surface, melting occurs along the base of the crustal block above the plume roof, resulting in the formation of a mushroom-shaped head of the plume, which means that a large intrusive body (deep-rooted batholith) is formed. The relative thermal power of such plumes is 1.9<Ka<10. Based on the laboratory and theoretical modeling results, we present the thermal and hydrodynamic structure of the thermochemical plume with the mushroom-shaped head. The parameters of some plumes, that are responsible for formations of batholiths in North Asia, are estimated from the geological data, including the age intervals and the extent of magmatism. Relying on the model of the flat horizontal liquid layer, hydrodynamics and heat transfer of the mushroom-shaped plume head are considered. The variations in temperature and flow velocity in the melt of the plume head are assessed. The compositional changes in the melt of the plume head are determined by stages: (1) after settling of refractory minerals; (2) after settling of plagioclase in the melt resulting from the first stage. The tables show the calculation data, including the weight contents of oxides and the normative compositions for the melts at T_melt=1410 °C and T_melt=1380 °C. The thickness of the residual melt is estimated for the case of the Khentei plume. Its head’s thickness (l) is equal to the plume conduit diameter (d): l=d=29 km. The proposed model of the plume with the mushroom-shaped head was used to calculate the normative composition of the melt with a chemical composition similar to that of normal granites.

The evolution of the ‘mantle – moving deformable continents’ system has been studied by numerical experiments. The continents move self-consistently with the mantle flows of thermo-compositional convection. Our model (two-dimensional mantle convection, non-Newtonian rheology, the presence of deformable continents) demonstrates the main features of global geodynamics: convergence and divergence of continents; appearance and disappearance of subduction zones; backrolling of subduction zones; restructuring of mantle flows; stretching, breakup and divergence of continents; opening and closing of oceans; oceanic crust recirculation in the mantle, and overriding of hot mantle plumes by continents. In our study, the continental crust is modeled by active markers which transfer additional viscosity and buoyancy, while the continental lithosphere is marked only by increased viscosity with neutral buoyancy. The oceanic crust, in its turn, is modeled by active markers that have only an additional buoyancy. The principal result of our modeling is a consistency between the numerical calculations and the bimodal dynamics of the real Earth: the oceanic crust, despite its positive buoyancy near the surface, submerges in subduction zones and sinks deep into the mantle. (Some part of the oceanic crust remains attached to the continental margins for a long time.) In contrast to the oceanic crust, the continental crust does not sink in subduction zones. The continental lithosphere, despite its neutral buoyancy, also remains on the surface due to its viscosity and coupling with the continental crust. It should be noted that when a continent overrides a subduction zone, the subduction zone disappears, and the flows in the mantle are locally reorganized. The effect of basalt-eclogite transition in the oceanic crust on the mantle flow pattern and on the motion of continents has been studied. Our numerical experiments show that the inclusion of this effect in the model considerably alters the pattern of mantle flows and leads to distinct changes in the evolution of continents. Moreover, a new effect arises – bulging of heavy material (eclogitized former oceanic crust) at the core-mantle boundary, wherefrom it arises with the mantle plumes on the surface of the Earth.