We announce the second edition of the Aerospace geological map of the Olkhon Region (Baikal, Russia), scale 1:40 000, which was published in 2017. The map has been considerably revised and updated, and its changes are critical for correct understanding of the regional geology, tectonics and geodynamics. Only a small number of its printed copies have been released, and therefore the map may not be available for all interested specialists. The electronic version of the map is available for studying and/or printing (see the link to its pdf file in the paper’s supplement). The pdf file is about 68 MB, i.e. small compared to the original map (more than 5 GB), but the quality is maintained. The map does not show the base layer due to the terms of the licenses owned by the companies and satellite owners.

The article presents the results of U-Pb isotope dating of detrital zircons from the Jurassic coarse rocks in the apex and the western slope of Mnt. Biyuk-Sinor (the southern wall of the Baidar basin, near the village of Orlinoe). These dates are compared with the detrital zircon dates obtained for sandy rocks from the Upper Jurassic coarse clastic strata composing the slopes of Mnt. Spilia near Balaklava Harbor and Mnt. Southern Demerdzhi near Alushta city, as well as the Middle Jurassic Bitak conglomerates near the village of Strogonovka (suburb of Simferopol city). The comparison shows a high degree of similarity of the averaged age characteristics of the main detrital zircon populations. Sandy rocks of Jurassic coarse clastic strata for zircon dating were sampled in four locations of the Mountaineous Crimea. Based on their dates and a summary set of ages of detrital zircon grains from sandstones of the Southern Coast of Crimea, spanning the stratigraphic interval from the Middle Jurassic to Neogene, we can provide a statistically reliable specification of the Carboniferous-Triassic time interval (360–200 Ma) of magmatic activity within the Black Sea region. This period was bounded in time by the Late Devonian and Early Jurassic relative magmatic lulls. None of the zircon grains of the Carboniferous-Triassic age has revealed Hf-isotopic characteristics indicating any significant contribution of crustal material older than the Mesoproterozoic into the protolith of the parent zircon rocks. Within the Carboniferous-Triassic interval of magmatic activity, three stages are distinguished: (I) 360–315 Ma, (II) 315–270 Ma, and (III) 270–200 Ma. Magmatic stage I (360–315 Ma) is related to the closure of the Reik ocean, which completed after the subducted slab ‘broke off’ into the mantle and was accompanied by the ubiquitously manifested HT-LP metamorphism. Zircon grains of stage I are characterized by peak ages of about 325–340 Ma and the dominance of negative εHf. Magmatic stages II (315–270 Ma) and III (270–200 Ma) correlate with functioning of the Scythian-Pontian volcanic suprasubduction belt. In these magmatic stages, zircon εHf values scatter from weakly negative to substantially positive (referred to the depleted mantle), which is typical for volcanic arcs. Fuzzy separation of stages II and III and strong variability of the peak ages of zircons from the studied samples (which we associate with these stages) can be due both to changes in magmatic activity in different segments of the belt, and to changes in the erosion intensity of crystalline complexes of the belt during the subsequent stages evolution caused by tectonic rearrangements within the Paleo-Tethys ocean and its peri-oceanic structures.

 

Granitoids of the Magdagachi complex were studied using new and published petrochemical, geochemical and isotopic (Sm-Nd, Rb-Sr) data. Granitoid samples were taken from the southern frame of the eastern flank of the Mongol-Okhotsk orogenic belt (MOOB). Their analysis shows increased concentrations of Sr, Ba, Eu; reduced concentrations of Nb, Ta; abnormally low concentrations of HREE, Y and Yb; significant fractionation of REE; and high Sr/Y ratios. Therefore, the Magdagachi granitoids are "classical" adakites that may have formed at a depth of more than 45 km due to melting of eclogite with a garnet content of 20–50 %. Such conditions could exist under subduction as a result of melting of the frontal or lateral parts of the slab in subduction windows formed during oblique subduction at an orthogonal sinking angle. Highly metamorphosed lower crust Precambrian formations were also melted, and a source of parental melts could have been composed of both the mantle and crustal materials. Two tectonic scenarios are proposed that could have been accompanied by the formation of Magdagachi granitoids. Both scenarios refer to subduction processes, but differ in interactions between various regional structures in the Late Mesozoic.

 

Block-granular geological objects and rock volumetric mobility indicators are described. The mechanisms of structural and material reworking of rocks are considered in relation to the formation of a discrete tectonic structure of rocks and changes in the shapes of the geological bodies, which take place without rupturing the rock surfaces bounding these bodies and provide for the volumetric tectonic flow of solid rocks. Based on the study of natural objects and their comparison with the theoretical and experimental data on solid mechanics and geomechanics, it is suggested that one of the triggers for the volumetric disintegration of rock masses is rock fatigue damage (a fundamental phenomenon of solid-state physics). The disintegrated rocks behave according to the laws of mechanics of granular materials and mesomechanics. This study is of both theoretical and pragmatic importance as it contributes to the understanding of the regional geological features and provides new knowledge on the formation of crystalline protrusions known among the main hydrocarbon reservoirs within the basements of various geologic structures.

 

The study was focused on the tectonic structure features of the Gulf of Aden, which includes three provinces. The western, central and eastern provinces differ in morphostructural segmentation of the spreading ridge of the Gulf of Aden, which took place in different geodynamic regimes of their formation and development. In our study, physical modeling was performed to investigate the segmentation mechanisms of the three parts and the formation of the marginal plateau and the island of Socotral. In experiments, an elastic-plastic plate lying on a liquid base (simulating melt) was subjected to normal or oblique stretchig. Plate sections imitating the continental or oceanic lithosphere in the model had different thicknesses. Various heterogeneities, such as cuts, linear weakened zones (rift heating zones) etc., were set in the plate sections in accordance with natural analogues. The modeling results show that morphostructural segmentation of the spreading axis in the Gulf of Aden depends on the degree of heating and the thickness of the lithosphere, associated with different distances from the Afar plume and local thermal anomalies, spreading obliquity and the existence of structural inhomogeneities with increased lithosphere strength, which are associated in this case with the presence of Mesozoic grabens on the pre-breakup basement. The smaller is the lithosphere thickness, the smaller is the size of the segments. The sharper is the angle, the more pronounced is segmentation.The study of the connection of the Gulf of Aden continental rift with the rift zone of the Carlsberg ridge suggests that during their development, these rift fractures propagated towards each other. The experiment results show that in case of a «sharp» boundary between blocks that differ in thickness, a shear zone is likely to occur. Such a case is applicable, for example, to the Alula-Fartak fracture zone, or to Owen’s fracture zone. With a less ‘sharp’ boundary, overlapping structures are often formed, such as microplates or microblocks enclosed between two rift fissures. In such case, one microblock then dies, while the other develops into a spreading ridge. Apparently, such a microblock is represented by the marginal plateau and the island of Sokotra. As shown by the modeling, propagation of the two rifts towards each other was important for the formation of the plateau and the island of Socotra. Moreover, a significant role was played by the initial geometry of the rift zones and their initial positioning separate from each other. 

Ground-penetrating radar (GPR) surveys were performed in the Sarma segment of the Primorsky fault between the settlements of Shida and Kurma. This segment belongs to one of the largest structures of the Baikal rift and was active in Late Quaternary (Early Holocene). The study aimed to reconstruct vertical displacement amplitudes and dip angles of fractures along the fault segment, clarify its kinematic type, and estimate a maximum magnitude of earthquakes that may occur in the study area. The GPR equipment set included an OKO-2 georadar and AB-250M and ABDL-Triton shielded antennas. The GPR surveys were supported by morphostructural and tectonophysical methods. Based on the interpretation of the geophysical survey data and satellite images, faults associated with the Sarma paleoseismic dislocation were mapped. Their total length amounts to 14 km. According to the GPR survey data, one-stage vertical displacements show normal faulting and vary from SW to NE from 4.4 to 7.7 m. Paleo-earthquake magnitudes calculated from the maximum displacement values (Mw=7.2, and Мs=7.4) suggest that potential earthquakes in the Primorsky fault zone may be stronger than previously assumed. 

The study of the White Sea region and the adjacent area aimed to model the structure of the crystalline portion of the crust at the contact of the northeastern slope of the Fennoscandian Shield and the Russian Plate. Modeling was based on geological, geophysical and DSS profile data, State Geological Map of the Russian Federation (scale 1:1 000 000), Explanatory Notes to Sheets Q-35, 36, 37, and 38 (third generation, 2009), and Tectonic Map of the White Sea and Adjacent Areas (2012). A model was constructed using GIS INTEGRO software (VNIIgeosystems), specifically its procedures for calculation and visualization of 2D and 3D models showing crust density and magnetic fields. The model of the study area shows the structure of the crust and the characteristics of its horizons.

An innovative technology of anomalous magnetic field inversion was applied to construct 2D models of the magnetic layer using three profiles crossing the southern, central and northern parts of the Kuril Island Arc. In the frontal area of the northern and southern parts, a zone of increased effective magnetization is clearly distinguished. In the central part of the island arc, increased magnetization is much less pronounced. Anomalous zones of positive effective magnetization have a deep part, the so-called "serpentinite wedge". The inhomogeneous lateral structure of the magnetic layer of the Kuril Island Arc suggests differences in the fluid regime and is reflected in the distribution of modern seismicity.

 

The study is focused on searching for spatial regularities in the occurrence of earthquake hypocenters in different geological settings in Northern Armenia. Tectonic-geomorphological indices are applied to define the tectonic activity of blocks composing the study area, which was manifested within a long period of time, starting from the neotectonic development period. The blocks are classified accordingly. The regional seismic activity is analysed considering the block structure of the study area. Earthquake focal mechanisms are determined, and dominant displacement trends are identified. Based on the comparative analysis of the blocks’ tectonic activity indicators and the locations of seismic events differing in strength, regular patterns of spatial distribution of seismic events are identified. It is established that the earthquake hypocenters of different strength occur in certain block structures; and the predominant types of movements in the earthquake hypocenters are largely determined by types of fault structures. It is emphasized that investigating the blocks’ neotectonic activity is important for discovering the general patterns of spatial distribution of seismic events.

Seismic intensity assessment in points of a macroseismic scale plays an important role for researching the seismic history of areas characterized by active seismicity, as well as for construction (and updating) of seismic zoning maps in various scales. Macroseismic scale points are generally referred to in construction standards applied in the majority of post-Soviet states. In our study aimed to model the macroseismic field of earthquakes, a large volume of macroseismic data on Central Asia was analyzed, and coefficients used in Blake–Shebalin and Covesligeti equations were aligned. This article presents a generalized dependence model of macroseismic intensity attenuation with distance. The model takes into account seismic load features determined by various depths of earthquakes. The ratios of small and big axes of the ellipse, that approximates real isoseists, are estimated with respect to seismic scale points, earthquake depths and magnitudes. The East Uzbekistan area is studied as an example to investigate whether seismic hazard assessment values may differ depending on a chosen law of seismic influence intensity attenuation with distance.

Core samples taken from the bottom sediments of the glacial Lake Kucherla (Gorny Altai, Russia) clearly show annual layers represented by glacial clays. In our study, age-depth modeling is based the varve chronology and Cs-137, Pb-210 and C-14 isotope data. Our model is a highly accurate and reliable demonstration of the annual sedimentation history within the past 1400 years. The time series of geochemical indicators of climate change were obtained by synchrotron radiation micro X-ray fluorescence (SR-μXRF) core scanning. Instrumental meteorological observations from 1940 to 2016 were used to construct transfer functions for the average annual temperatures and atmospheric precipitation amounts. A geochemical trace of a catastrophic seismic event, the Mongolian earthquake of 1761, was found in the cross-section of the bottom sediments.

The southern deformed edge of the Siberian paleocontinent is studied for zoning the disturbance of ²³⁴U/²³⁸U cyclic equilibrium in groundwaters discharged to the accreted Khamardaban terrane. A relationship is established between vertical variations of ²³⁴U/²³⁸U (ОА4/8) activity ratios and the hydrogeochemical zoning of groundwaters. Lateral ОА4/8 zoning of groundwaters in the basement rocks and sedimentary cover of the Siberian platform is described. It is emphasized that an important role is played by the water propagating from the South Baikal reservoir (SBR) (ОА4/8 = 1.95–1.99; U content = 0.44–0.46 μg/L) under the shore of Lake Baikal. It is suggested that the lateral advancement of the SBR water is facilitated by the development of low-angle (weakened by rifting) fractures of the Angara thrust fault, as well as subvertical fractures in the shear zone of the Main Sayan Fault. Monitoring data on the study area show that the ratios of the groundwaters components vary in time due to Cherdyntsev – Chalov deformational effect, chemical interaction of the waters and evaporites, and mixing of the groundwaters with contrasting hydrogeochemical signatures.

This study of groundwaters of the Altai Republic is relevant due to the need to identify earthquake precursors in seismically active zones of the study area. Chemical composition of groundwater is widely known as an indicator of seismic processes, which changes in future earthquake focal zones. In this regard, studying helium contents in groundwater is of particular importance – anomalous concentrations of helium are typical of fault zones, and helium concentration variations in time can be referred to as earthquake precursors.

Our study was focused on the distribution of helium in groundwaters of the Altai Republic and aimed to determine and justify positioning of permanent monitoring sites for investigation of earthquake precursors.

During the field study, groundwater samples were taken from wells and springs located within the area covered by the established state monitoring network (GONS). Groundwater aquifers and water-bearing zones from Quaternary to Proterozoic ages were sampled.

Analysis of the groundwater samples shows spatial variations of helium concentration in the study area. Water samples from fault zones have increased concentrations of helium. The concentration of helium is high in the groundwater from the Chuya artesian basin, i.e. near the epicentral zone of the M 7.5 Altai (Chuya) earthquake of September 27, 2003.