Subject of study. Different points of view on the concept of structures of the terrain type and their role in the addition of orogenic belts are considered. Materials and methods. We used our own research and analysis of the latest publications about the Ural-Timan region and the Pacific belt, on the territory of the Northeast segment of Eurasia, as well as currently known isotope radiometric data. It was used also the result of geophysical seismotectonic and paleomagnetic explorations. Results. It has been established that in the composition of the Ural-Timan structural area, along with the Proterozoic and Paleozoic associations of the orogenic belts and the Riphean sedimentary series of protrusions of the Russian Plate, structural formations that correspond to the terrain of the continental crust take part. They are the most characteristic for the Ural orogenic belt, which belongs to the group of epiokean-type belts, associated with the transformation of ocean basins with the active participation of accretion and collision processes. The parametric features of these terrains include the ancient age characteristics of terrain rocks, their position in the belt structure, as well as the presence of relics of subhorizontal layered structural elements. The discordant blocks of migmatites, gneisses and other metamorphic rocks of Precambrian age, which make up the terrains, was the basis for the introduction of the term “terranes of the ancient continental crust”. By connection with the source, exotic and endemic, and simple and complex terrains are distinguished by structure. The geodynamics of including terrains of the ancient continental crust into the structure of orogenic belts is associated with horizontal movements of fragments of the ancient lithosphere in oceanic paleobasins to the periphery of the Russian Plate and their localization in belt structures. The formation of these terrains in the structures of the orogenic belts is completed by the formation of the intra-terrain massifs of granitoids and belts of volcanic-intrusive series. Supporters of a different methodology, dominant among researchers of the Pacific Belt of the Northeast Segment of Eurasia, refer to terrains all the structural elements that perform orogenic belts, because they believe that they have undergone horizontal movements and are in allochtonous occurrence. Conclusions. It has been established that in different geological provinces the term terrain has its own characteristics. This was the basis for the selection of two geodynamic types of terrains.

The object of research. The main goal of the work was to resolve the problem of the existence of rock associations: alkaline granites–syenites–nepheline syenites, which is found on all continents among ancient platforms and stabilized folded regions of different ages. Beginning with 70-th. of the past century, the absolute majority of the world's petrologists do not allow the possibility of a comagmatic formation of such a rock association due to the presence of a thermal albite “barrier” between phonolitic and rhyolitic melts. Materials and methods. Numerous data were used on the Ilimaussak alkaline massif from southern Greenland as the most thoroughly studied and widely known to petrologists around the world. The main methods of research were the development of physicochemical models of phase transitions and the construction of state diagrams. Results. Earlier, thanks to the author's work in the field of constructing state diagrams, the possibility of “destruction of thermal barriers” was demonstrated at the appearance of alumosilicate melts of biotite, amphibole, analcime and other minerals on the liquidus. The developed physicochemical models of phase transitions for specific rock associations of the Ilimaussak massif allowed us to prove the possibility of a comagmatic transition from nepheline-modal syenites to quartz-modal alkaline granites. Conclusions. The validity (correctness) of the theoretical constructs is proved by an almost perfect coincidence of the model and natural trends of the rock associations. This requires a certain composition of the initial melt and the optimal fluid pressure.

Object. Geochemical features of rocks from the Dal’ny Tulkas and Mechetlino sections located in the southern part of the West Urals foredeep are considered and are offered as International Standards for the global correlation (GSSP) of the lower boundaries of the Artinskian and Kungurian stages. Materials and methods. The content of rock-forming oxides and other components were studied for 15 and 20 samples of carbonate, clay and sandy rocks respectively in the sections of Dalnii Tyulkas and Mechetlino. The determination of the chemical composition of rocks was performed using a wave-dispersive X-ray fluorescence spectrometer S8 Tiger (Bruker, Germany). Results. The lithological characteristics of the sections, the content of oxides in mudstones and limestones of the boundary Sakmarian-Artinskian and of the boundary ArtinskianKungurian are taken. Mudstones of different stage are almost identical in average contents of the main components, whereas limestones have some differences. Correlative connections of oxides are analyzed and conclusions about mineral composition of rocks are made. Using the petrochemical modules and diagrams, it was established that the clay rocks in considered sections have mainly a hydromica composition. Based on the analysis of the indices of chemical weathering CIA, it is shown that the climate in the Cisuralian Epoch was predominantly arid. The tectonic environment of forming demolition sources, presumably corresponded to the active and passive margins of the continents. Conclusions. The main lithochemical characteristics of the rocks of the two sections under consideration are somewhat different, however, the boundaries of the stratigraphic subdivisions of each of them are virtually indistinguishable by lithochemical parameters, which may indicate the benefit of the continuity of sedimentation at the borders of centuries of the Cisuralian Epoch in this region. The conditions of sedimentation and the nature of eroded rocks in the area of demolition remained relatively constant. This is a positive point when looking the sections as International Standards for the global correlation (GSSP) reference objects – “golden nails”. 

Subject of the study. We have carried out an additional exploration on petrography, petrochemistry, geochemistry, geochronology and biostratigraphy of rock complexes of the Yugansk-Koltogorsk (central part of West Siberia). Materials and methods. The materials are core samples from wells that penetrated the Pre-Jurassic basement rock complexes The used methods are as follows: X-ray spectrum microanalysis (Cameca SX 100, JEOL-733 Superprobe); the silicate analysis of the rocks (СРМ-18 and EDX-100); mass-spectroscopy with inductively coupled plasma (ICP-MS) (ELAN-9000 and Element2); zircons were analysed with a high resolution ionic microprobe SHRIMP-II (U-Pb); Ar-Ar dating was carried out by Micromass 5400; biostratigraphy, petrochemestry. Results. A geological map of Yugan-Koltogor zone of the central part of West-Siberian plate in a scale 1:500 000 was created. The map is a set of informational geological, geophysical and other layers. It was established that age of granites is Early Permian, the basalts of the rift zone began to form 268.4 ± 7.5 Ma ago (Ar-Ar). Conclusions. Volcanism in the axial rift zones of the West-Siberian megabasin basement began earlier than it is supposed before our study and significantly earlier of that of trap basalts of Siberian platform.

Object of study. The article presents of the petrographic study results of the garnet-containing rocks from the Ufaleiskii complex, located on the border of the Ufaleyskii metamorphic gneiss-amphibolite block with the Main Ural Fault (GUR). Methods. Petrographic studies were conducted using a polarizing microscope Axiolab ZS и Olimpus BX 51. Chemical composition of garnets is performed on the raster electron microscope of the РЭММА-202М with an energy dispersive spectrometer LZ-5. Results. Investigations made it possible to distinguish two types of garnet-containing rocks. One type, in which garnet was formed after amphibole (amphibolites and gornbendites), and the second one, in which garnet is the primary mineral (metamorphic schists). Zoisite and chlorite are formed in rocks of the first type together with granate. CaO, MgO, FeO and Al2O3 were extracted from amphibole, in the process of crystallization of garnet, some of these components went to form zoisite and chlorite, and the released silica formed quartz. Garnet grains in these rocks are 64–68% composed of almandine. In the rocks of the second type, represented by biotite-hornblende, biotite-chlorite-quartz and double-mica schists, garnet is the primary mineral formed from the original rocks in the process of progressive metamorphism. The composition of the garnet in these rocks correlates with the composition of the original rock. Conclusion. A complex of garnet-containing rocks with a high content of granulated quartz may be of interest as a raw material for obtaining pure quartz concentrates. The paper presents the results of a detailed petrographic study of all types of rocks of the complex and discusses possible options for their genesis.

Object of study. The paper presents the mineralogical and petrographic study results of metamorphosed and metasomatized komatiites and komatiitic peridotites from the Ozerki soapstone deposit and Pentinsuo prospect, located in the Kostomuksha greenstone structure of the Karelian Craton, Fennoscandian Shield. Material and methods. Surface and drill core samples of various mineral and structural-textural varieties of altered komatiites were studied by optical microscopy, electron microscopy with an attachment for microanalysis, XRD phase, thermogravimetric and chemical analysis. Results. Soapstone formation in the investigated localities displays a multistage alteration and associates with the superimposed alteration of Mg-rich metakomatiite flows and olivine cumulates due to influx of carbon dioxide bearing fluids enriched in calcium and potassium. The chemical composition of initial komatiite (MgO content of the rock) and the degree of its fracture intensity are the main factors controlling soapstone formation. In differentiated lava flows soapstone is formed mainly in high-magnesium cumulate zones characterized by a high content of serpentine. In the flow top and spinifex zones an early amphibole-chlorite-magnetite mineral association is preserved in varying degrees. Talc and carbonate are formed by the decomposition of serpentine and amphibole. The chlorite content in soapstone is controlled by the Al2O3 concentration in the respective flow zones. Conclusion. The carbonate-chlorite-talc is the general natural type of soapstone associated with thin komatiite lava flows of distal volcanic facies. In more thick proximal lava flows the formation of soapstone of chloritecarbonate-talc and talc-carbonate composition is possible. The most prefered prospecting areas for soapstone are fields proximal to the eruptive vent, main lava conduits and subvolcanic analogues of komatiites.

Subject. The paper is devoted to the study of the gold-silver-palladium-platinum mineralization of the streaky systems in the sedimentary rocks associated within the Triassic carbonaceous silicites of the Taukhinsky and Samarkinsky terranes of the Sikhote-Alin. Materials and methods. In the process of investigations we studied the metamorphosed carbonaceous siliceous-clay rocks and systems of the mineralized fractures in the Triassic siliceous-clay and siliceous (including jaspers) rocks of Shirokopadninskaya, Vysokogorskaya and Gornaya areas, as well as in the sandstones (unclarified age) of Gornaya area. The samples for the analytical study were taken with the lump way. To estimate the content of precious metals in the rocks, cut by the systems of the mineralized fractures, we used the fire assay and atomic-absorption methods. The analyses of minerals (in polished sections) have been done using the JXA-5A and JXA8100 microanalysers. Results. The gold-silver-palladium-platinum mineralization in the siliceous and clay-siliceous rocks, as well as in the sandstones is restricted to the systems of the mineralized fractures and by many features are analogous to the precious-metal mineralization of the black-shale formations. It is represented by native forms, disordered solid solutions, and intermetallic compounds of different metals. The specificity of the Au-Ag-Pd-Pt mineralization is a wide distribution of copper gold, Ni-, Cu-, and Pbbearing gold, and Zn-bearing platinum. Native elements and intermetallic compounds, including those of precious metals, are not rarely associated with the organic matter testifying to the active participation of carbon and, probably, hydrogen that provided the high- and ultra-reduction character of the processes of mineral formation. Conclusions. The presence of the mineral forms of different maximum reduced metals is caused by the influence of the organic matter of the Triassic carbonaceous silicites. This consisted in the removal of the most volatile components, and first of all the poorly bound water and hydrocarbons from the carbonaceous rocks through the contact metamorphism related with the injection of the granitoid intrusions of Cretaceous plutonic and volcanoplutonic belts.

Object. Multi-proxy analysis of 265 cm long sediments core of Lake Turgoyak, one of the deepest lakes of the Southern Urals, is presented. Materials and methods. The lake ecosystem changes was reconstructed based on diatom, radiocarbon dating and geochemical analysis. Statistical treatment of the surface sediments composition and hydrochemistry data of 56 lakes from Southern and Middle Urals lakes database allowed to obtain geochemical indexes for reconstruction of water parameters: index of organic matter content (ОМ = LOI550ºС/(Al2O3 + TiO2 + Na2O + K2O)) and index of salinity (ММ = LOI950ºC/LOI550ºС). Results. Radiocarbon dating shows that sedimentation in Lake Turgoyak was began more than 12 cal kyr BP ago. Each of six lithological units of sediments core is characterized by its own geochemical features and associated with global (11.8, 11.2, 8.2 cal kyr BP) and regional (12, 10.3 cal kyr BP) climate events of the Northern Hemisphere. Four main stages of Lake ecosystem development were identified: 1) the beginning of lake sedimentation (>12.1 cal kyr BP); 2) the stage of a subsaline shallow-water lake (12.1–11.2 cal kyr BP); 3) the stage of a freshwater lake with increased water-level (11.2–8.0 cal kyr BP); 4) the stage of water organic matter increase (<8.0 cal kyr BP). Conclusions. High content of mesohalobic diatoms and salinity module values showed significant increase of lake water salinity as response to Early Holocene climate warming (11.8–11.2 cal kyr BP). Pantle-Buck’s Saprobity Index and OM values pointed to the lake water organic matter increase due to the next climate warming since 9–8 cal kyr BP. Thus, Lake Turgoyak water parameters were reapeatedly changed during the Holocene. However the response of lake ecosystem was different in different periods of its development.

Object of research. The aim of this work was the comparative analysis of element composition of groundwater (drip, fracture), water from the interior of the watercourse in a karst cave Proshchal’naya (Khabarovsk Territory) and the surface water of the nearest river Sagdy-Selanka. The great interest was the study of speleothem (dropstones) “moon milk” in the cave Proshchal’naya. Materials and methods. Speleothem “moon milk” was investigated with a scanning electron microscope (EVO-40HV, CarlZeiss, Germany) and silicon-drift x-ray detector X-MAX 80 мм2 . By ICP-MS method a comparative analysis of element composition of groundwater (drip, fracture), water from an internal stream in the cave Proshchal’naya and surface water of the river Sagdy-Selenka were carried out. Results. Maximum concentrations of calcium, iron and manganese was installed in the spring, between drip and fracture water and magnesium – in flowing waters (inland watercourse caves and Sagdy-Selanka R.). It was determined that visually plastic and homogeneous mass of speleothem “moon milk” is heterogeneous and contains various microstructures. Tubular microstructures were represented by richer elemental compo sition (C, O, Ca, Fe, Mn, Si, Al, and S) compared with club-shaped formations (C, O, Ca, and Na). The binding matrix in the composition of the “moon milk” were reticular structures similar to actinomycente mycelium and bacterial films. Findings. The results of studies conducted in a monsoon climate may be interesting for researchers which study karst processes in other climatic zones.

Author’s guide.