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.

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.

Zoning of high mountainous areas by geoecological loads caused by geodynamic and climatic influences

Геотектонические, литологические и ландшафтно-морфологические особенности территорий, функционирующих туристско-рекреационных комплексов Центрального Кавказа, определяют платформенный характер развития Скифской плиты, южной окраиной вовлеченной совместно с причлененными микроплитами-террейнами (Предкавказская, Бечасынская, Восточно-Кавказская) в горообразовательный процесс Большого Кавказа. Иной характер геологического развития претерпели территории южного склона Большого Кавказа, вовлеченные в горообразовательный процесс как океанические плиты – террейны (Закавказская плита, Южная микроплита – сложенные толщей чередующегося флиша глинистых сланцев с прослоями песчаников, мергелей, известняков). Прижатая к жесткой Скифской плите с юга Закавказской плитой, подпираемой Аравийской платформой, Южная микроплита подверглась интенсивной деформации, глубинным тектоническим проявлениям субширотной ориентировки, являющимся каналами активного проявления эндогенных геодинамических процессов. Создание туристско-рекреационного комплекса на Южном склоне Центрального Кавказа предполагает прогноз темпов геоэкологической эволюции в условиях активной геодинамики и интенсивного проявления опасных геологических процессов. Цель исследований – зонирование интенсивностей уровней геоэкологических нагрузок геодинамических и климатических воздействий для дифференцированного целевого использования соответствующих площадей. В процессе исследований выявлены геодинамические и климатические факторы, характерные для территории и реализовано ранжирование интегральных воздействий на исследуемой территории. Методика заключалась в разбиении территории на элементы площади размерами 4×4 кв. км, учете значимых факторов воздействия на элемент площади и суммировании интенсивностей, определяемых экспертными оценками ранжирования, обусловленных каждым из природных воздействий. В процессе решения задач были определены геодинамические и климатические факторы, характерные для территории; дифференцированы геотектонические и геоморфологические условия их проявления; проведена экспертная оценка интенсивности воздействия каждого фактора по пятибалльной системе и установлен суммарный максимально возможный потенциал воздействия. Результаты исследований стали основой составления соответствующей карты – схемы зонирования исследуемой территории на зоны с интенсивностями, характеризующими различные уровни геоэкологической нагрузки. The geotectonic, lithological and landscape-morphological features of the territories where tourist and recreational complexes are functioning in the Central Caucasus determine the platform nature of the development of the Scythian plate. The southern margin of this plate is involved, together with the attached microplate-terranes (Ciscaucasia, Bechasynskaya, East Caucasian), in the mountain-forming process of the Greater Caucasus. The territories of the southern slope of the Greater Caucasus, involved in the mountain-forming process as oceanic plates - terranes (Transcaucasian plate, South microplate - folded by a layer of alternating flysch of clay shales with interlayers of sandstones, marls, limestones) have undergone a different character of geological development. The Southern microplate is pressed against the rigid Scythian plate from the south by the Transcaucasian plate, supported by the Arabian platform. It has undergone intense deformation, deep tectonic manifestations of sublatitudinal orientation, which are channels for the active manifestation of endogenous geodynamic processes. The creation of a tourist and recreational complex on the southern slope of the Central Caucasus presupposes a forecast of the geoecological evolution rate in conditions of active geodynamics and intensive manifestation of dangerous geological processes. The Aim of the study is the zoning of the intensity levels of the geoecological loads of geodynamic and climatic influences for the differentiated target use of the corresponding areas. In the course of research, geodynamic and climatic factors characteristic for the territory were identified and the ranking of integral impacts on the studied territory was implemented. The methodsconsisted in dividing the territory into area elements of 4 × 4 square km., taking into account the significant factors of influence on the element of the area and summing up the intensities determined by expert estimates of the ranking caused by each of the natural impacts. In the process of solving the problems, the geodynamic and climatic factors characteristic for the territory were determined; differentiated geotectonic and geomorphological conditions of their manifestation; an expert assessment of the intensity of the impact of each factor was carried out according to a five-point system and the total maximum possible impact potential was established. Results of the study became the basis for the compilation of the corresponding map - the zoning scheme of the study area into zones with intensities characterizing different levels of geoecological load

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.

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.