Scythian Plate Research Articles

Boundary of recent activation and seismicity on the platform part of Ukraine

The purpose of the work is to clarify the boundaries of the recent activation (RA) zone in the platform part of Ukraine. Such limitations are evident for the Alpine Carpathian geosyncline and the Hercynian-Cimmerian Scythian plate. For the East European Platform, the edge of the zone is determined by the magnitude of the mantle gravity anomaly. This option gives a more definite result than the previously used complex of geological and geophysical data. The applied technique, in addition to the usual two-dimensional density modeling along DSS profiles, includes the processing of the obtained data by kri­ging. This allows you to fill in the area between the profiles and trace the detailed shape of the zone boundary. The magnitude of the anomaly at the edge of the active region was calculated. In the center of the zone, the studied perturbation (the difference between the gravitational effect of the crust and the observed field) is 30—40 mGl, at the edge — 20 mGl. An estimate of the error in determining the anomaly was made, it turned out to be at the level of 10 mGl. The value at the boundary is less than the tripled error. In this situation, a special procedure is needed to detect spatial variations in the position of the boundary. For this, for the first time, two of its calculation options were used: using kri­ging and using artificial profiles located between the real ones. The crustal sections under the artificial ones were average between the real ones, the observed field on the artificial profile was used. An average difference in the boundary position of 13 km was obtained. The practically important question of the ecological consequences of manifestations of activity in the RA zone on the platform is considered. Seismicity does not pose a significant threat, as does the release of helium with anomalous isotopy and hydrogen. Catastrophes happen precisely during the exploitation of gas and coal deposits, and not as a result of the natural evolution of these objects.

Южная граница Скифской плиты в системе блоковой делимости консолидированной коры Центрального и Восточного сегментов Большого Кавказа

Актуальность работы. В региональном плане граница кристаллической коры сближающихся плит определяет стиль коллизионного процесса и особенности его эволюции. В большинстве предложенных коллизионных моделей формирования структуры Большого Кавказа предполагается, что Скифская плита является упором для смещающейся в северном направлении Аравийской плиты. Граница Скифской плиты и Закавказскай микроплиты также во многом определяла региональную тектонику Центрального и Восточного сегментов Большого Кавказа. Всвязи с этим установление южной границы Скифской плиты на уровне кристаллического основания является актуальной проблемой. Цель работы заключается в оценке положения глубинной южной границы Скифской плиты, перекрытой осадочными породами Центрального и Восточного сегментов мегаантиклинория Большого Кавказа, по анализу блокового строения консолидированной коры. Методы исследования. С целью оценки южной глубинной границы Скифской плиты выполнена интерпретация геолого-геофизических материалов на площади в тектоническом отношении отвечающей Центральному, Восточному и Юго-Восточному сегментам, обрамляющим их предгорным прогибам и структурам Скифской плиты на севере, а в южной части – Закавказской системе впадин и срединных массивов. Методы и методика работы заключались в комплексной интерпретации материалов (гравиметрических, сейсмических исследований по профилям ГСЗ и ММЗ, обобщения данных по тектоническому строению). Результаты работы. Показано, что консолидированная кора Центрального и Восточного сегментов Большого Кавказа принадлежит к Черноморско-Каспийскому геоблоку, разделенному продольным Сването-Алазанским разломом на Тырныауз-Кубачинский и Джава-Ширакский мегаблоки, характеризующие соответственно южный фланг Скифской плиты и северный фланг Закавказской микроплиты. К южному флангу Скифской плиты приурочена большая часть мезозой-кайнозойского осадочного комплекса Центрального и Восточного сегментов. Южная граница Скифской плиты на уровне консолидированной коры в пределах Центрального и Восточного сегментов Большого Кавказа выражена Сването-Алазанским фрагментом Большекавказского межплитного разлома, который разграничивает Скифскую плиту от Восточно-Черноморской и Закавказской микроплит. Relevance. In regional terms, the boundary of the crystalline crust of the approaching plates determines the style of the collision process and the features of its evolution. Most of the proposed collision models for the formation of the Greater Caucasus structure assume that the Scythian plate is a stop-block for the northward shifting Arabian plate. The boundary of the Scythian plate and the Transcaucasian microplate also largely determined the regional tectonics of the Greater Caucasus Central and Eastern segments. In this regard, the establishment of the Scythian plate southern boundary at the level of the crystalline base is an urgent problem. Aim. The purpose of this work is to estimate the position of the deep southern boundary of the Scythian plate, overlain by sedimentary rocks of the Central and Eastern segments of the Greater Caucasus megaanticlinorium, by analyzing the block structure of the consolidated crust. Methods. In order to assess the southern deep boundary of the Scythian plate, an interpretation of geological and geophysical materials was carried out in the area tectonically corresponding to the Central, Eastern and South-Eastern segments, framing their of the foothill troughs of Scythian plate and structures in the north, and in the southern part ‒ the Transcaucasian system of depressions and median arrays. The methods and methodology of the work consisted in the complex interpretation of materials (gravimetric, seismic studies on the DSS and MMS profiles, generalization of data on the tectonic structure). Results: It is shown that the consolidated crust of the Greater Caucasus Central and Eastern segments belongs to the Black Sea-Caspian geoblock, divided by the longitudinal Svaneto-Alazani fault into Tyrnyauz-Kubachi and Java-Shirak megablocks, characterizing the southern flank of the Scythian plate and the northern flank of the Transcaucasian microplate, respectively. Most of the Mesozoic-Cenozoic sedimentary complex of the Central and Eastern segments is confined to the southern flank of the Scythian Plate. The southern boundary of the Scythian plate at the level of the consolidated crust within the Central and Eastern segments of the Greater Caucasus is expressed by the Svaneto-Alazani fragment of the Bolshekavkazsky interplate fault, which delimits the Scythian plate from the Eastern Blackseas and Transcaucasian microplates

Deep structure and tectonics of the South Ukrainian monocline in the zone of juncture of the East European platform and the Scythian plate (according to gravimetric data)

In order to investigate the deep structure and tectonics of the central part of the South Ukrainian monocline (SUM), a detailed study of this structure was carried out using a network of gravimetric profiles. It is shown that on the part of the SUM, which belongs to the southern edge of the East European Platform (EEP), the basement is split into separate blocks with different characteristics of the consolidated crust. The crust of the Scythian Plate (SP) within the SUM has undergone considerable changes as a result of tectonic activation and significant complications of its structure. The distribution into the areas with different density characteristics of the basement of EEP and SP does not coincide, indicating that the development of the latter has not been fully inherited from the former. The obtained results, compared with data from other researchers in Prydobrydzha and Crimea, show that the northwestern shelf is an intermediate link between these terranes. A tectonic scheme of the research area based on the hypsometry of the surface of the second layer of the basement was built on the basis of the simulation. It was shown that the southern edge of the platform has undergone rather insignificant transformations, which are manifested in the emergence of an elongated intracrustal graben system along the EEP/SP boundary, divided by sublatitudinal faults into three blocks with different parameters. At the northern margin of the SP within the SUM, in addition to the grabens and horsts in the basement, there are sags and uplifts with boundary faults without vertical crustal displacements along them. Areas of the heterogeneous-heterochronous structure of the crust of the Baikal, Hercynian, and Kimmerian generations have been identified within SUM part of the SP. It has been determined that the Golitsyn fault system and the northern flank of the Karkinit trough were further restructuring during the Alpine tectogenesis phase. A variant of the Scythian Plate origin scenario based on the Mobilist ideas is proposed and substantiated by the results of the conducted studies and the available geological and geophysical information as a discussion.

Geoelectric Model of the Central Part of the Northern Caucasus and Its Fluid Saturation

A series of magnetotelluric and seismic studies have been carried out on profiles covering more than two thousand kilometers within the North Caucasus region. The earlier interpretation of the magnetotelluric observations by means of one– and two–dimensional inversion and three–dimensional mathematical modeling software has helped to construct a series of sections and models which are viewed as test and starting ones for the construction of a three–dimensional geoelectric model of the region. The test models have been used to test how well the software for three–dimensional inversion of the impedance tensor components in the magnetotelluric sounding method can estimate the parameters of conducting blocks in the structures of the Greater Caucasus and the Scythian plate. In the resulting geoelectric model, constructed from the results of three–dimensional inversion of all impedance tensor components, the position of low–resistance blocks correlates with deep faults, volcanoes of various genesis, and seismically active zones characterized by the reduced velocity of seismic waves and their increased absorption. The electrical resistivity of low–resistance anomalies is explained by the degree of their saturation with the fluid water fraction. Its maximum concentration is found within the intersections of fault systems, flexural–rupture zones, and deep faults activated by tectonic processes.

Temperature distribution in the crust and upper mantle of the territory of Ukraine

The study aims to build a three-dimensional thermal model of the crust and upper mantle of the territory of Ukraine. Its basis is a scheme of deep processes in the tectonosphere, which, first of all, considers the results of heat and mass transfer during modern activation. They are superimposed on the models of the platform (except for the territory of the East European platform; the Donbas is also included in it), the Alpine geosyncline of the Carpathians, and the Hercynian-Cimmerian geosyncline of the Scythian plate. The incomplete process of modern activation cannot be accurately described by the geological theory used by the authors. Gravity modeling was previously conducted on a system of profiles around the northern hemisphere with a total length of more than 30,000 km, crossing Eurasia, North America, as well as the Atlantic and Pacific oceans to select an adequate scheme of heat and mass transfer. The paper distinguishes the most realistic scheme of the process . It is applied for Ukraine, and the more accurately the activated area is determined. Such a task was solved for the first time. In the south, the model is limited by the Black Sea depression, at a depth of 400 km. Temperatures in the transition zone to the lower mantle were not considered. Test thermal models are compared with geothermometers. The error (50°C) of calculation and cross-section of isotherms is determined (150°C for depths from 50 to 400 km, at a depth of 25 km the error is lower, the cross-section of isotherms is 100°C). Zones of partial melting of the rocks of the crust and upper mantle have been established. They are distributed in the middle part of the crust, in the upper horizons of the mantle (50-100 km). At a depth of about 400 km, partial melting occurs only under the non-activated part of the platform. Differences in the model from the presented one are described. They are associated with possible variations in the age of the process and its peculiarities at different levels of heat and mass transfer. Practical significance. The study emphasizes that mineral deposits are characteristic to thermal anomalies and other environmental parameters.

Geotraverse «Granite—Odesa—Kryvyi Rih—Pereschepine

The article examines the results of research carried out by the methods of reflected waves and common depth point (MRW-CDP) on the «Granit» geotraverse, which crosses the whole of Ukraine from the southwest to the northeast and passes through the territories of Odesa, Mykolaiv, Dnipropetrovsk, and Kharkiv regions, west of Belgorod region of Russia. In structural and tectonic terms, the geotraverse crosses large geological structures: the marginal part of the Scythian Plate (SP), the Ukrainian Shield (USH), the Dnieper-Donetsk Basin (DDB) and the southern slope of the Voronezh Crystalline Massif (VCM). The analysis of the features of the registered wave field and the completed structural constructions of the consolidated crust and upper mantle in the section of the «Granite» geotraverse shows a complex heterogeneous structure with certain spatially correlated regularities, against the background of which there are numerous inhomogeneities characteristic of both individual blocks and their individual intervals. The cross-sections of all the studied geostructures are characterized by a high level of saturation with non-extended, unevenly distributed reflective elements, which occupy positions from subhorizontal to steeply sloping in space. With all the diversity of the mutual location of both individual boundaries and their groups, a fairly strict correlation is established, which primarily provides information about the nature of stratification, deformations, and the stress state of the structures of the consolidated crust and upper mantle. In the modern structure of the crust, a significant role belongs to faults and tectonic plates, the vast majority of which are manifested as inclined zonal bodies with different orientations. Systems of faults and plates form a complex hierarchical interdependence. The «crust-mantle» transition zone is a complex, laterally variable area, with a thickness of 3 to 7 km, caused by systems of subhorizontal stratification, expressed by the concentration of reflective elements. The largest homogeneous and contrasting region of the transition is manifested in the structures of ancient consolidation, with a thickness of the crust of about 40 km. As a result of the research, more detailed information on the structure of individual tectonic elements was obtained, and some general principles of the structure of the transition zone from the ancient continental platform to the active folded belt were clarified.

Locating the southern boundary of the East European Platform within the north-western Black Sea shelf according to gravimetric data

The work is devoted to the problem of determining the position of the border of the East European Platform (EEP) and the Scythian Plate (SP), which is of great economic importance in dividing the north-western shelf of the Black Sea into more and less promising areas for hydrocarbons. An analysis of the allocation of the juncture of EEP and SP using 23 literature sources published from 1985 to 2020 was performed. The essential differences in drawing the relevant line by different authors are shown. A method for determining the position of the southern boundary of the EEP within the north-western shelf of the Black Sea is proposed, based on the integrated use of gravimetry data — characteristic features of the gravity field (Δgf.a.) and the results of systematic two-dimensional density modeling. The outcome of modelling allowed determining the position and nature of the EEP and SP junction in the section of the earth’s crust, which turned out to be a transcrustal fracture of the southern falling with angles of inclination from 83.5° to 85.5° in different parts of the shelf. According to calculations of the exit points of the faults on the basement surface superimposed on the scheme Δgf.a made it possible to identify the spatial position of the junction of EEP and SP and its extension outside the modeling area for the entire study area. It is established that this line has a zigzag character, changing direction at the intersection with submeridional faults. It is shown that the formation of the southern boundary of EPS was controlled, except for the submeridional component characteristic of EPS, by three other systems — latitude, directions NE-SW and NW-SE, which are observed for tectonic elements of SP in Pridobruzha and Crimea. The correctness of the determination of the boundary position by gravimetric data is confirmed by the results of seismic stratigraphy and thermometry previously obtained by other researchers.

Rhyolites of the Kiliya-Zmeinyi uplift on the Black Sea shelf: geochemical evidence of a non-subduction boundary between the East European Platform and the Scythian Plate

The geochemistry of rhyolites uncovered at shallow depth by a borehole on the Kiliya-Zmeinyi uplift of the Black Sea northwestern shelf northeast of Zmeinyi island, in the junction zone of the East European platform and the Scythian plate, has been studied for the first time. This zone is considered by many geologists and geophysicists as a Late Paleozoic collisional suture that had been formed due to subduction of oceanic crust of the ocean, which adjoined the East European platform from the south, under the Scythian plate; it is traced from Dobrudzha to the Caspian Sea and named North Crimean. To check the subduction nature of the boundary between the East European platform and the Scythian plate, igneous rocks’ geochemical characteristics beeng indicators of various geodynamic regimes were used. A petrogeochemical comparison of rhyolites from the borehole in Zmeinyi area with acid igneous rocks known nearby has been carried out, namely with: 1) Late Permian subalkaline granites and rhyolites Turcoaia of the Macin zone of Northern Dobruja; 2) Triassic and / or Triassic-Jurassic trachyrhyolites and rhyolites of the Tulcea zone of Northern Dobruja and the Tatarbunar complex of the Pre-Dobruja depression. Some acid rocks of various ages and genesis from the southernmost margin of the Scythian plate (southwestern Crimea on- and offshore) were taken additionally for comparison. According to the distribution of rare earth elements, the position on the discriminant geochemical diagrams and the shape of curves on the multicomponent spider diagrams, the rhyolites of the Kiliya-Zmeinyi uplift exhibit not subduction but intraplate geochemical features closest to those of granites and rhyolites Turcoaia of the Macin zone of Northern Dobruja. Considering that the latter are reputed to be Late Permian, one can assume the same age for the rhyolites from the borehole in Zmeinyi area. Taking into account section features, geophysical information and geochemical similarity of magmatism, Kiliya-Zmeinyi uplift of the northwestern shelf seems to be a continuation of the Northern Dobruja structure into the Black Sea; it was a part of the hypothetical Late Paleozoic Euxinian orogen near its northern boundary. An absence of subduction geochemical properties in the studied presumably Late Permian rhyolites indicates that the junction zone of the East European platform and the Scythian plate in the Ukrainian shelf area is not a Late Paleozoic suture, but rather represents a thrust of the Euxinian orogen.

Analysis of change in hydrogeological conditions in Tyrnyauz tungsten–molybdenum field

Tyrnyauz tungsten–molybdenum deposit is located within the Elbrus volcanic region, on the left bank of the river Baksan. The deposit is associated with a series of granitoids formed during the period of activation of tectonic–magmatic processes at the southern boundary of the Scythian plate in the Meso-Cenozoic, and embedded in carbonate, terrigenous and volcanic rocks of the Devonian, Carboniferous and Jurassic. Groundwater that forms the drainage runoff is mainly fissure or fissure-vein water. In the field, groundwater belongs to an integrated system, within which, subject to the feeding conditions, and to the nature of circulation and chemical composition, two hydrogeological zones are clearly distinguished alongside with a mixing subzone between them. Between 1964 and 1997, the average annual water inflow into the underground openings of Molybdenum Mine varied from 122.4 m3/h in 1965 to 629.0 m3/h in 1986. In recent years of observations, the average annual water inflow ranged from 427.0 m3/h (1993) to 420.0 m3/h (1997). According to the measurements in October–November 2018, the water inflow in Molybdenum Mine was 494.3 m3/h. By the data of VIOGEM, in mid-September 2020, the inflow of groundwater into the mine amounted to 571 m3/h. The temperature of drainage waters in the Central ore field of the deposit, on the upper level of 2767 m during the study period ranged from 4.0 to 5.0 °C. Infrared photography using thermal imager detected hidden glaciers and flows of cold groundwater inside the rock mass.

Features of generation, migration and accumulation of hydrocarbons in the eastern part of the Skythian plate

The article shows the main spatio-temporal regularities of the development of the processes of generation, migration and accumulation of hydrocarbon fluids in the eastern part of the Scythian plate. The authors studied the features of the generationaccumulation hydrocarbon systems of the northern platform side - the Karpinsko-Mangyshlak and East Ciscaucasian oil and gas regions based on the application of technologies of basin analysis and modeling of hydrocarbon systems. The research results indicate that the following hydrocarbon systems are distinguished in the sedimentary cover of the eastern part of the Scythian plate: Jurassic, Cretaceous, Paleocene-Eocene, and Oligocene-Miocene systems. Based on the results of the studies and modeling, the main directions of further prospecting and exploration work in the eastern part of the Scythian plate were determined. The study area was differentiated by the nature of the predicted oil and gas content, the age of the promising complexes and the confinement to tectonic structures and zones. Keywords: generation; migration; accumulation; hydrocarbons; Scythian plate; hydrocarbon systems; basin analysis; modeling; source rocks.

The use of Middle Jurassic mudstones of the Dzhangur Formation as a Possible Raw Material in the Ceramic and Construction Industry

The article provides information about the field studies in the incision that folded with the Dzungur Formation mudstones of the Labino-Malkinskaya zone in the Scythian plate of the Central Ciscaucasia. The accumulation stages and post-sedimentation transformation have been researched. The field data of the petrographic research and the prospects of their possible implementation as raw materials in the construction is presented in this article.

Deep structure, tectonics, evolution and hydrocarbon potential of the north-western shelf of the Black Sea along 31°20’E

A density modeling of the north-western shelf of the Black Sea along 31°20’ E was carried out. According to its results, a complex block structure of the area is determined, which is closely connected with the history of its development. Signs of Baikal tectonic activation of the southern edge of the pre-Riphean Eastern European platform, as well as the adjacent part of the Scythian plate have been revealed. Areas formed during the Hercynian and Cimmerian epochs of tectogenesis have been identified within the Scythian plate. At the base of the Karkinit Trough, two areas of reduced crust resulting from riftogenesis with varying degrees of intensity of basification have been established. Two ancient volcanos of ryolite composition were found on the basement surface on the northern slope of the Kalamit swell. It is highly probable that the Gamburtsev uplift is an eastern extension of the Gubkin swell. According to the structure and value of the calculated densities, it is established that the Gamburtsev uplift is a «blind» mud volcano, which was formed during the second stage of the late Cimmerian cycle and was active throughout the Cretaceous period. A detailed analysis of the deep structure and fault tectonics of the local structures of the sedimentary cover in the intersection of the profile and the area of gas seeps was carried out. It was found that the Flangova, Partizanska and Hamburtseva structures are more promising for hydrocarbon accumulation. The hydrocarbon potential of the Ushakov structure (H-41) is questionable, because structurally and tectonically it is analogous to the Delphin structure, which was deemed unproductive based on drilling results. The area of gas seeps was found to be confined to a mantle fault, which separates two blocks with distinctly different structures and Meso-Cenozoic evolution of the Earth’s crust. It is proposed to conduct a detailed seismic survey in this area in order to identify local structures in the sedimentary cover, promising for hydrocarbons.

ІНТЕРПРЕТАЦІЯ 3D ГЕОЕЛЕКТРИЧНОЇ МОДЕЛІ НАДР СТЕПОВОГО КРИМУ. ЄВПАТОРІЙСЬКИЙ ТА САКСЬКИЙ ПРОФІЛІ

The interpretation of the segment of the deep three-dimensional Crimean region geoelectrical model within the Saki and Yevpatoria profiles, built on the basis of the Earth's low-frequency electromagnetic field experimental observations, was obtained in 2012 by the INSTITUTE OF GEOPHYSICS named after S.I.Subbotin. The main result of the analysis is the identification of vertical and horizontal alternation of high and low resistivity, both in the earth's crust and in the upper mantle. It is shown that the geoelectrical sections along all the profile sections of the model are characterized by a dip to the north of the consolidated basement surface depth and, accordingly, an increase of the near-surface layer conductivity. The conductivity anomaly in the consolidated earth's crust was revealed in the depth interval of 5-10 km with resistivity (ρ) of 5 Ohmꞏm, galvanically connected with the sedimentary cover. Deeper than 10 km, homogeneous and inhomogeneous layers in ρ alternate: 10-60 km with ρ = 1000 Ohmꞏm; 60-90 km with ρ = 100 and 1000 Ohmꞏm; 90-110 km with ρ = 1000 Ohmꞏm; 110-140 km with ρ = 40 and 1000 Ohmꞏm, the contact corresponds to the different ρ of normal geoelectrical sections of different-aged structures of the Scythian plate and the East European platform; also horizontally layered normal section. It has been analyzed that earthquake sources of the Steppe Crimea seismic region are concentrated in geoelectrically inhomogeneous zones and tend to contact structures with ρ differ - above the upper margin, outside and between the conductivity anomalies in the consolidated rocks of the earth's crust. The considered material confidently indicates the confinement of hydrocarbon manifestations to the high electrical conductivity anomalies identified according to the data of geoelectromagnetical sounding and three-dimensional modeling, which are characterized by subvertical channels galvanically connected with sedimentary deposits, and layering in the earth's crust and upper mantle. Geoelectrical inhomogeneities, which reflect the current state of the earth's crust and upper mantle and are probably due to the influence of modern mantle fluids, correspond to manifestations of seismicity and hydrocarbon content.

Seismic Tomography Model for the Crust of Southern Crimea and Adjacent Northern Black Sea

This new seismic tomography study for the crust of southern Crimea and the northeastern Black Sea based on low-magnitude (M ≤ 3) earthquakes indicates significant heterogeneity of the crust at depths of 15–35 km. In the present paper we discuss the velocity distribution for P- and S-waves and give geological and tectonic interpretations in the context of collisional interaction between the Black Sea microplate and the Scythian plate. The joint use of data on both types of waves (P- and S-waves) increases the reliability of the interpretation and allows us to estimate the crustal composition of Mountainous Crimea (MC) and subcrustal mantle of the northeastern Black Sea. We have detected high velocity regions in the MC crust (Vp = 6.5‒6.8 km/s, Vs = 3.7‒3.9 km/s, Vp/Vs = 1.75‒1.9), which have complex configurations and can be deep sources of mid-Mesozoic intrusions known in the MC (Ayu-Dag and Castel). The high-velocity area is separated from eastern Crimea by a linear nearly north–south low-velocity zone located between the cities of Sudak and Feodosiya. The latter is interpreted as a weakened crustal zone associated with the Korsak–Feodosiya fault. The high-velocity region beneath the Black Sea (south of Kerch Peninsula) at depths of 25–40 km most likely belongs to the subcrustal mantle (Vp/Vs = 1.80–1.85) that underlies a thin suboceanic crust of the East Black Basin. The resulting crustal model for southern Crimea and adjacent part of the Black Sea is consistent with the parameters of other geophysical fields.

Density inhomogeneity of the Earth’s crust of the Black Sea and adjacent territories from three dimensional gravity modelling. Part II. Density sections

To obtain a more complete picture of the deep structure and density heterogeneity of the main tectonic structures of the Black Sea megadepression and adjacent territories, density sections were constructed that intersect structures along geotraverses, DPS profiles and illustration profiles. Based on the results of three-dimensional gravity modelling, the Scythian plate has a block structure, more complex than the East European platform. It is also characterized by a thick layer of deformed sediments, with the largest compaction of the crust is being in its western and southern parts. The pre-Dobrudzha Trough consists of two parts: the denser one, which adjoins the Serpentine Rise, and the less dense one, adjacent to Zmeiny Uplift. The Karkinitsky Trough is characterized by compaction of the middle and lower parts of the Earth's crust in the south and west, that is associated with tectonic processes during riftogenesis, namely, the introduction of mantle matter into the lower and middle parts of the Earth's crust. There is no «granite» layer under the Black Sea-Kalamitsky Swell, the «basalt» layer is represented by a crust-mantle mixture. The deep domain of the Indolo-Kuban Trough is divided into two blocks along the axis: denser (south, west and southwest) and less dense (northeast, east and north). In Crimea, in all density sections a thick layer of dislocated sediments is observed, the crystalline crust is characterized by significant compaction (especially the southern part), the absence of a «granite» layer, the occurrence of the subsurface «basalt» layer and the presence of the thick crust-mantle mixture. The West Black Sea Depression is characterized by the absence of a granite layer in the central part, the occurrence of sediments on the «basalt» (and sometimes on the «diorite») layer. In this case, the crust is of the oceanic type. In the East Black Sea basin there is a thin layer of dislocated deposits with a density close to the density of crystalline rocks. According to the density value, this layer can be attributed to very compact dislocated deposits that suggests the oceanic or rifted continental crust. The crystalline crust of the Central Black Sea Rise is heterogeneous in composition and structure. The Andrusov and Arkhangelsk Ridges, which echelonedly displaced to each other, have different density characteristics of the crystalline crust, the depth of its bottom and density on it. Collectively, these features give evidence of the heterogeneous history of the formation and development of these structures. The Sinop Depression is a large Neogene graben which is underlain by a crust-mantle mixture of different thickness. The Sorokin Basin is characterized by an increased thickness of the sedimentary cover, the absence of a «granite» layer and a rise in the roof of the «diorite» layer to a depth of 2―3 km in the eastern part, as well as the presence of a «granite» layer with a thickness of over 10 km in the western. The northwestern part of the Shatsky Uplift is characterized by decompression of the entire Earth's crust, and in the southeastern part, decompression is observed only in the middle part of the section.

The structure of the lithosphere, tectonics and evolution of the Scythian Plate and adjacent structures in the section of the Bs05-22 profile (according to 2-d density modeling)

A density model was built along the Bs05-22 profile, which made it possible to identify individual blocks with different crustal parameters. The consolidated crust of the East European Platform (EEP) has a “key” structure. The southern boundary of the EEP is clearly fractured and falls to the south at an angle of about 83° The South Ukrainian monocline (SUM) covers not only the basement of the EEP but also the northern part of the Scythian Plate (SP). The central part of SP block overlapped by the SUM is characterized by the maximum capacity of the folded-metamorphic base. The axial part of the Karkinit Trough (KT) has a structure typical for riftogens. The rift is practically one-sided with a width of 6.5 km. The southern slope of the KT developed as a result of the falling of the surface by the mechanism of the planj-principle. The border between the Karkinit Trough and the Kalamitsky rise (KR) is clearly defined by the Sulinsko-Tarkhankutsk fault. The core of the KR is a sufficiently massive body of lenticular shape with a density corresponding to the Taurian series of the Mountainous Crimea. There is a narrow transition zone between KT and Edge step (ES). The southern edge of the Scythian plate is a 25,0 km wide transition zone to West-Black Sea depression (WBSD). Modeling established the extension of the “granodiorite” layer into the WBSD for 100 km. The crust thickness within the EEP is 44,0 km, on the Scythian plate under SUM is average 43.5 km, 37,0 km within KT and 33,0 km under ES, in the West Black Sea basin 28,7 km under the foot of the Upper Cretaceous continental slope and 21,5 km at the southern edge of the profile. In the model chosen, the density of tectonic faults in the EEP is 0,06 and in the SP — 0,14 per 1,0 km. Vertical shifts of crystalline crust blocks at SP reach 5,5 km, which is almost three times higher than at the southern flank of the EEP. The most of disjunctions are vertical and have transcrust stretch. The structure of the Earth’s crust obtained as a result of modeling allowed us to draw some conclusions about the Meso-Cenozoic evolution of the studied region in the profile section. At the southern edge of the EEP in the Late Cimmerian tectogenesis epoch there has been a revitalization, in the Alpine phase this structure was generally passive. Activity of the Cimmerian epoch was observed throughout the Scythian plate: within the Kalmitsky rise from the early phase, and in the Karkinit Trough and on the Edge step from the late Cimmerian phase. The periods of activation on the KT and KR are traced up to the Sawa phase, and on the ES — to the Walach phase of the Alpine tectogenesis inclusive.

Age, HF-isotope systemantics of detritial zircons and the source of conglomerates of the mt. Southern Demerdzhy, Mountainous Crimea

The U–Pb dating and Hf isotope systematics of detrital zircons from a sandstone interbed in the section of the upper conglomerate sequence of the Mt. South Demerdzhi were carried out.
 The dominant populations of detrital zircons in the studied sample characterize episodes of magmatic activity within the source of the Upper Jurassic conglomerates. Magmatism was manifested in the Vendian-Cambrian, Carbon-Triassic and Late Jurassic. The åHf values of detrital zircons of these ages indicate the insignificant role of the ancient (Archean–Early Proterozoic) continental crust in the protolith of magmatic chambers. The similarity of the detrital zircons age distribution from the Middle Jurassic and Upper Jurassic conglomerate strata suggests that they are molasses of the Cimmerian orogen. The absence of products of Middle Jurassic magmatism in molasses of the Cimmerian orogen, which we fixed, limits position of the Cimmerian orogen in the southern part of the Scythian plate. It is shown that the primary source of the Precambrian detrital zircons were mobilized within the Cimmerian orogen the crustal fragments of the Peri-Gondwanan origin, rather than the basement complexes of the East European Platform, similar to the complexes of the Ukrainian shield.
 The reconstruction of the main stages of the accumulation of the coarse-grained strata of the Mountaineous Crimea in the context of the tectonic evolution of the southern margin of Laurasia during the Mesozoic is presented.

Age, Hf-Isotope Systematic of Detrital Zircons and the Sources of Conglomerates of the Southern Demerdzhi Mountain, Mounatinous Crimea

The U–Pb dating and Hf isotope systematics of detrital zircons from a sandstone interbed in the section of the upper conglomerate sequence of the Mt. Southern Demerdzhi were carried out. The dominant populations of detrital zircons in the studied sample characterize episodes of magmatic activity within the source of the Upper Jurassic conglomerates. Magmatism was manifested in the Vendian-Cambrian, Carbon-Triassic, and Late Jurassic. The eHf values of detrital zircons of these ages indicate the insignificant role of the ancient (Archean–Early Proterozoic) continental crust in the protolith of magmatic chambers. The similarity of the detrital zircons age distribution from the Middle Jurassic and Upper Jurassic conglomerate strata suggests that they are molasses of the Cimmerian orogen. The absence of products of Middle Jurassic magmatism in molasses of the Cimmerian orogen, which we fixed, limits position of the Cimmerian orogen in the southern part of the Scythian plate. It is shown that the primary source of the Precambrian detrital zircons were mobilized within the Cimmerian orogen the crustal fragments of the Peri-Gondwanan origin, rather than the basement complexes of the East European Platform, similar to the complexes of the Ukrainian shield. The reconstruction of the main stages of the accumulation of the coarse-grained strata of the Mountaineous Crimea in the context of the tectonic evolution of the southern margin of Laurasia during the Mesozoic is presented.

Seismotectonic Model of the Northwest Caucasus: Geological-Geophysical Aspect

In connection with the seismic hazard assessment of the Black Sea coast of Russia, the problem of the formation of seismicity in the Northwest Caucasus in the context of recent kinematics of the East Black Sea microplate is relevant, and the boundary of the microplate with the Scythian plate, in our opinion, should be considered among the most debatable issues. This problem is studied based on the tectonic scheme of the consolidated crustal layer of the Northwest Caucasus relying on the analysis of the geological and geophysical data. It is shown that the interplate boundary is represented by the Crimean and West Caucasian faults and that the crust of the Scythian plate is tectonically stratified in the region of the plate interaction which led to the overthrusting of its layers with the subsequent isostatic downwarping of the Moho to a depth of 55 to 60 km beneath the Greater Caucasus Orogen. The tectonic structure of the northeastern flank of the East Black Sea microplate is determined by the Anapa and Sochi blocks having significant excess density. The formation of seismicity of the Northwest Caucasus is mainly associated with the reverse stresses created by the seismogenic Anapa and Sochi blocks and with the tectonic stresses in the zone of the West Caucasian interplate fault. The area of the Anapa and Sochi blocks is at most 4000 square kilometers, which constrains the limiting source size and the maximum (6.0) magnitude of the earthquakes.

Tectonic structure of the zone of conjugation of the Eastern European piatform and the Scythian plate (territory of the Rostov region)

The tectonic structure in the junction zone of the East European and Scythian platforms of Rostov region has been considered. Different ages and ranks of Precambrian and Phanerozoic tectonic structures, their correlation within the studied area and tectonic zoning scheme are presented. The structure and composition of rock complexes, formation conditions and their tectonic development stages are characterized. The East European platform within the described territory is represented by two disconnected fragments of the Russian Plate. The northern fragment is the south-eastern part of the Voronezh anteclise, located to the north of the Donetsk-Astrakhan tectonic suture. The southern fragment corresponds to the eastern dipping of the Pre-Paleozoic rocks of the Ukrainian shield, forming the buried Rostov ledge. The Scythian (Epihercynian) platform located to the south of the Donetsk-Astrakhan tectonic suture, is represented by a folded Paleozoic (in some places pre-middle-Jurassic) base and a platform cover of Mesozoic-Cenozoic rocks. The part of the Scythian platform is the exposed Donbass area, where Paleozoic rocks of the base of the platform protrude to the surface and form the Donetsk ledge. The northern part of the Scythian plate, which extends over the buried folds system of Donbass, is allocated from the south by Manych over-fault deflections and called «Karpinsky shaft». The system of the Manych deflections and the territory located to the south compile the Ciscaucasian part of the Scythian plate.