Research subject. The Polar Urals seismic transect area. Aim. To develop and consider a new gravitational computer model of the Polar Urals seismic transect, containing 29 layers and 225,388 cells. Methods. Geological, gravity and magnetic, and seismic data on the Polar Urals seismic transect (A.V. Rybalka et al.); the authors’ modeling method. Results. A new geological and geophysical model was developed. This model refines the existing ideas on the geological structure of the Polar Urals and the basement (Pre-Jurassic basement) of the Western part of the West-Siberian plate along the Polar Urals seismic transect to the depth of 15 km. Our studies have confirmed the high quality of works on the Polar Urals seismic transect headed by A.V. Rybalka. The developed model gives a more detailed representation of the structure of the Earth crust along the transect. The geological map of the basement of the Pre-Urals part of the West-Siberian plate was refined. Thus, according the geomagnetic map, we included numerous arrays of serpentinite; in granite-gneiss, we allocated different density areas (2.67 + 0.06, 2.67 + 0.02, 2.67 + 0.09 g/cm³); in the North part of the map, the model consist of four  group of the rock of different density 2.67 + 0.12, 2.67 + 0.05, 2.67 + 0.06 and 2.67 + 0.08 g/cm3; this formation to the Source-East of the transect is modeled by rocks with density 2.67 + 0.19, 2.67 + 0.06, 2.67 + 0.14, 2.67 + 0.06, 2.67 + 0.04 g/cm³. We also introduced granite of the gabbro-granite formation mainly northward of the city of Salekhard. Cenotypal effusive Triassic rocks (mainly basalt) join to them from North-West and Source-East. In the Source-East corner of the map we introduced gabbro and unweathered ultrabasite. Conclusion. A 3D density model in the vicinity of the Polar Urals seismic transect using an anomalous magnetic map was developed. The geological map of the region was clarified.

Research subject. The Voimakan deposit of dolomite type nephrite. Aim. Determination of the mineral composition and development of a model for the formation of nephrite. Materials and Methods. 12 samples of nephrite and 5 samples of host rocks were studied. A binocular, a gemological lantern, a magnifying glass, and a petrographic microscope were used. The mineral composition was studied using a scanning electron microscope with an energy dispersive quantitative microanalysis system. Results. Nephrite is light salad, salad, gray-salad and brown (honey). It forms segregations in calcite-tremolite skarn bodies at the contact of dolomite marble and amphibolite transformed into epidote-tremolite skarn. Nephrite minerals are classified as parageneses: relict (minerals of dolomite, amphibolite and skarns): dolomite, magnetite, uraninite, fluorapatite, zircon, epidote I; metasomatic before nephrite: diopside, quartz I, okermanite, olivine; metasomatic nephrite: calcite I, tremolite; regressive metasomatic: quartz II, serpentine, talc, chlorite, epidote II; secondary: anglesite, vanadinite, wulfenite, hollandite (?), sylvin, uranophane, native bronze, copper, silver. Conclusion. Nephrite meets the requirements for gemstone raw materials. Intensive replacement with chlorite and, especially, talc has been developed, which significantly worsens the quality of raw materials. Diopsidite with nephrite lenses, interlayers can be used for carving multicolored products or inlays. A model of nethrite formation is presented with the initial formation of diopside on dolomite, its replacement by tremolite or calcite-tremolite aggregate; the early prismatic tremolite is replaced by a tangled fibrous cryptocrystalline tremolite. Skarn calcite can also be replaced by tremolite to form nephrite. With the continuation of the regressive process, tremolite is replaced by chlorite or talc in association with calcite.

Research subject. The Syum-Keu ultrabasic massif, located in the Polar Urals. Aim. Identification and disassembly of deformation events near the junction of different-age structures of the Urals, Pay-Khoy, and the northwestern part of Western Siberia. Materials and Methods. Geological interpretation of data on the geometric characteristics of fold structures, paleostress indicators, anisotropy of magnetic susceptibility, and ⁴⁰Ar/³⁹Ar dating of muscovite. Results. The study of the structural characteristics of rock complexes in the Syum-Keu ultrabasic massif and its framing confirmed the presence of several stages in their deformation: (1) a stage of plastic deformation (early collisional stage) and (2) two stages of brittle deformation (late collisional stage). During the early collisional stage, thrusting with a shear component took place, which is manifested in shallow folding hinges and orientations of the main axes of the anisotropy of magnetic susceptibility ellipsoid. The late collisional stage reveals early NE-SW strike-slip compressional stresses and late NW-SE strike-slip stresses corresponding to strike-slip and strike-slip displacements. The results of ⁴⁰Ar/³⁹Ar dating of granitoids indicate the Turnean age of metamorphic transformations. Conclusions. The conducted study of mesostructural elements revealed two types of deformations: early plastic deformations, attributed to the early collisional stage and reflecting regional thrusting, and late brittle deformations, attributed to the late collisional stage and reflecting thrust and thrust movements. The study of the orientation of the ellipsoid anisotropy axes of magnetic susceptibility of rocks in the western and eastern margins of the Syum-Keu massif showed thrusting and strike-slip kinematic characteristics of the complexes, which are typical of the early collisional stage and the formation of the Ural cover structure in accordance with the Hansen model. The results of ⁴⁰Ar/³⁹Ar dating may indicate metamorphic transformations of rocks in connection with the onset of collisional processes in the Polar Urals, presumably of the Turnean age.

Research subject. Carbonate rocks in the frame of the Suunduk granite-gneiss massif of the East Ural uplift (Southern Urals). Aim. Determination of possible petrological and geochemical zonation in carbonate rocks of the metamorphic frame of the granite-gneiss massif. Identification of structural regularities of distribution and the character of relationships between carbonate rocks of different types. Materials and Methods. Expedition works were carried out using the methods of field structural geology and mineralogy. Samples of carbonate rocks were selected along the profile transverse to the strike of rocks. The contents of petrogenic elements were determined by X-ray fluorescence analysis using CPM-35 and EDX-8000 spectrometers; rare and trace elements were determined by ICP-MS using an inductively coupled plasma ELAN 9000 mass spectrometer. Results. Carbonate rocks are represented by calcite marbles, Mg-calcite marbles, dolomite marbles, calcite-dolomite marbles, and organogenic marmorized limestones (C_1–2). Zonality in the carbonate framing of the southern part of the massif was identified, apart from metamorphic zonality: marbles and marmorized limestones in the distance. At the early collision stage, a terrigenous-carbonate sequence was formed. At the end of C₂, due to regional metamorphism and formation of a granite-gneiss dome structure, in the areas of movement of metamorphogenic fluids, limestones underwent Mg-metasomatosis with the formation of pre-metamorphic dolomites with relics of fauna of C_1–2 age. As a result of progressive dynamothermal metamorphism, under stress conditions, metasomatic dolomites in places experienced dedolomitization, with the formation of calcite marble with a polygonal-grained structure; this marble was also formed on limestones. Under stress, calcite marble was squeezed out along weakened zones in the direction of pressure drop, i.e. upward. This process was associated with plastic and quasi-plastic deformations, metamorphic recrystallization, metasomatic alterations. Mg-calcite marble with accessory red corundum, phlogopite, Cr-tourmaline, and Cr-muscovite was formed in the areas of movement of metamorphogenic fluids. At the early regressive stage, Mg-metasomatosis reappeared in the fluid movement areas with the formation of dolomite-calcite marble with accessory graphite, tremolite, Cr-tourmaline, and pyrite. The lack of a pronounced zonality of marbles in the frame of the granite-gneiss massif can be explained by the duration and variety of marmorization processes. Conclusion. The granite-gneiss massif was the center of zonal metamorphism. At the progressive and regressive stages of metamorphism, the earlier- middle-carboniferous limestones in the frame of the massif underwent metamorphic and metasomatic transformations with the formation of marbles of various compositions; there were plastic and quasi-plastic deformations, rheomorphic displacements of calcite marble. There is no obvious zonality in the marbles.

Research subject. REE-containing minerals in metamorphic pre-Cambrian rocks of the northern part of the Lyapinskii anticlinorium of the Subpolar Urals. Aim. To establish typochemical features and conditions for the formation of rare-earth minerals in the studied rocks. Materials and methods. Chemical compositions and photographs of minerals were obtained using a JSM-6400 scanning electron microscope with a Link energy spectrometer and a Tescan Vega 3 LMH with an Instruments X-Max energy-dispersive attachment. The content of rock-forming oxides was determined by the gravimetric chemical method. The contents of rare and rare-earth elements were determined using an Agilent 7700x inductively coupled plasma mass spectrometer. Results. Rare earth carbonates and titanoniobates were identified in the pre-Cambrian rocks of the Subpolar Urals. In the mica garnet-bearing crystalline schists of the Nyartinskii complex, ankylite-(Ce) and hydroxylbastnäsite-(Ce) were identified for the first time, and hydroxylbastnäsite-(La) was identified in the actinolite-bearing quartz-albite-epidote-chlorite schists of the Puyva Formation. In the metarhyolites of the Sablegorskii Formation, the typochemical features of bastnäsite-(Ce), kainosite-(Y), and аeschynite-(Y) were studied. Ankylite-(Ce), hydroxylbastnaesite-(Ce), and hydroxylbastnaesite-(La) from Lower Proterozoic and Upper Riphean metamorphic rocks were probably formed during metamorphogenic-hydrothermal processes in the presence of minerals containing rare-earth elements and with the participation of carbon dioxide solutions. A scheme for the formation of rare-earth minerals was proposed for the metarhyolites of the Upper Riphean-Vendian Sablegorskii Formation. Aeschynite-(Y) was probably formed as a result of the transformation of rhyolites, due to the presence in the residual melt of increased concentrations of some rare metals, i.e., Zr, Nb, Y, and REE. As a result of metamorphogenic-hydrothermal processes, bastnäsite-(Ce) replaces allanite-(Ce). Kainosite-(Y) in metarhyolites is the latest mineral, formed due to the recrystallization of allanite-(Ce) and bastnäsite-(Ce) during the decomposition of аeschynite-(Y). Conclusions. The study of REE-containing minerals in Precambrian rocks of the Lyapin anticlinorium found that rare-earth titanoniobates were formed during the post-magmatic stage of metarhyolite transformation. The formation of rare-earth carbonates may be associated with metamorphic and hydrothermal processes.

Research subject. Zircon of granites in the western contact part of the Adui massif (Middle Urals). Aim. To obtain new U-Pb dating and to clarify the geochronological model of the Adui granite massif. Methods. U-Pb dating of zircon was established using a SHRIMP-II high-resolution secondary ion microprobe (VSEGEI Research Center, St. Petersburg). The major and trace elements were determined using SRM-18, SRM-25, and VRA-30 X-ray fluorescence spectrometers and an ELAN-9000 mass spectrometer with inductively coupled plasma. Results. In terms of chemical composition, the vein granites in the western contact zone belong to the rocks of the granite-leucogranite formation that make up the massif. Their hosting gneisses possess features similar to the granitoids of the gabbro-tonalite-granodiorite-granite formation. Zircons from orthogneisses were found to have a simple structure and a close Th/U ratio (0.6) with wide variations in uranium and thorium contents. Their concordant age ranges from 290–270 million years. Such a wide age range may be due to the loss of lead during metamorphism. The zircon of granites is different. It consists of cores, often clastic in appearance, overgrown with a rim of high-uranium zircon. Zircon grain cores from early (pegmatoid) granites are similar to those from host orthogneiss and can be interpreted as captured from them. The cores of zircon grains in late granites are characterized by a rather low Th/U ratio (0.1) and wide variations in U contents; their dates form a single age cluster with an average concordant age of 270 Ma. The rims, which are characterized by high U concentrations and low Th/U ratios, mark the period of granite formation in the range of 265–250 million years. Conclusions. The interpretation of new and previously published age data consists in identifying a prolong stage of metamorphism and migmatization of the host rocks in the range from 290 to 270 million years, preceding granite formation. The completion of granite formation with the formation of the main phases of the Adui massif corresponded to a time interval of 265–250 million years.

Research subject. Sandstones in the Listvenny and Marcheta Formations of the Zasur’ya Series, Gorny Altai. Aim. Reconstruction of the parent rocks and geodynamic position of the sedimentation basin of sandstones of the Zasur’ya Series. Materials and Methods. The stratigraphic position of greywackes was studied. Petrographic descriptions were carried out using whole-rock compositions obtained by X-ray fluorescence (XFR) analysis. The obtained data were analyzed; classification diagrams were compiled. Results. The geological position of the sandstones of the Listvenny Fm. (Molchanikha Locality) and Marcheta Fm. (Marcheta Locality) shows their sediments as part of an accretionary complex. Planar and vertical cross-sections for both localities were constructed. According to petrographic and geochemical data, the sandstones correspond to greywackes, i.e., first-cycle sedimentation rocks. The provenance of the Listvenny sandstones was dominated by intermediate and felsic rocks. The provenance of the Marcheta sandstones was dominated by mafic to intermediate igneous rocks. Conclusions. According to the studied geological and geochemical data, the greywackes of the Listvenny and Marcheta fms. were formed by destruction of an intra-oceanic arc. The sandstones of the Listvenny Fm. accumulated in a back-arc basin, and the sandstones of the Marcheta Fm. accumulated in a forearc basin.

Research subject. Vein carbonate-magnetite-serpentine rocks with nests of gem garnet (demantoid) among antigorite serpentinites of the Korkodinsky massif in the Middle Urals. Aim. To characterize the composition of native gold and physicochemical conditions of its formation in a previously undescribed type of gold mineralization in ultrabasic rocks. Materials and methods. Grains of native gold from carbonate (calcite)-serpentine (clinochrysotile) veins with demantoid and host serpentinites were examined by scanning electron microscopy (JSM-6390LV by Jeol) and X-ray microanalysis (Cameca SX 100 with five-wave spectrometer). Results. Significant differences in the morphology and chemical composition of native gold grains from serpentinite and carbonate-serpentine veins were revealed. In serpentinite, these differences are represented by Au–Cu intermetallides, i.e., AuCu3 auricupride and AuCu tetraauricupride. The intermetallide compositions are close to stoichiometric with a Cu excess of up to 0.1 p.u. Rare inclusions of electrum (37–44 wt % Ag, sample grade 555–617‰) are present in tetraauricupride; copper and nickel sulfides are present in auricupride. Sulfide inclusions are represented by accretions of digenite (Cu/S = 1.88) with pentlandite, as well as digenite with flame-like phenocrysts of bornite-digenite solid solution. In the peripheral parts of auricupride grains, hypergene rims of up to 100 µm in thickness were detected. Hypergene gold in reflected light is brown in color, having a porous, collomorphic or monolithic-cracked structure. This gold is characterized by low Cu contents (1.4–10.6 wt %), relative to the primary auricupride composition (50.7–52.3 wt % Cu), a deficit of total components ranging from 1.5 to 20.0 wt %, and the presence of an oxygen line on EDX spectra. The grains of native gold from the vein carbonate-serpentine mass are composed of Au–Ag solid solution particles, belonging to high-grade gold (913–961‰, 4–10 wt % Ag), less frequently to lower-grade gold (808–866‰, 13.0–19.4 wt % Ag). Mineral inclusions in silver gold were not found. Conclusions. Differences in the composition of native gold from vein mass and serpentinite reflect the variability of physical and chemical conditions of its deposition. The deposition of Au–Cu intermetallides occured from fluids with low oxygen and sulfur fugitivities: log fS₂ = –8…–20, log fO₂ = –26…–39, and Au-Ag solid solutions under higher values of sulfur fugitivities and more oxidized conditions. It is assumed that cuprous gold is associated with antigorite serpentinization, when the hyperbasite body was in the depth. During its rise to the surface and decompression, reducing conditions were replaced by oxidizing conditions. As a result, the fluid became carbonic acidic. In such conditions, carbonate-serpentine veins with demantoid and native silver gold were formed. The presence of auricupride hypergene replacement products of collomorphic, porous and fractured structure, as well as the presence of oxygen line in EDX spectra testify both to the processes of redistribution of micropores formed during copper removal and a possible formation of oxide or hydroxide forms of gold and copper.

Research subject. The possibility of creating an external biochronological scale in stratigraphy is discussed. Materials and methods. Factors that ensure the independence of the events selected for constructing a biochronological scale from the geological setting of their occurrence are analyzed. Results. A category of biochronological scales, which are constructed based on studying evolutionary changes in a certain part of the skeleton, homologous to members of a long-existing group of organisms, was distinguished. Such scales are proposed to be referred to as meronomical. The specifics of constructing meronomical scales based on the study of conodonts is discussed. The evolutionary sequence of fossil species ensures the continuity of the scale and its external indicating status, which implies the independence of the scale from the facial features of the sections compared with its help. The main features of divergence arising in the process of evolution in the competitive relationships of related species are discussed. The correspondence of the main features arising in the development of skeletal elements during the evolution of conodonts with the prediction based on the accepted model of an ensemble development of related species is shown. In particular, such features include an increase in the variability of platform elements and stabilization of the morphology of ramiform elements, as well as a directed change in Pa elements, which serves as the basis for constructing conodont meronomical scales. The evolutionary morphological trend of the Pa element, which arises in the process of competitive relations between related species, does not depend on the particular external abiotic conditions in which these relationships are carried out. Accordingly, the biochronological scale built on the basis of the evolutionary trend of the Pa element states can also be considered as external in relation to the measured geological events captured in specific sections. The facts of the brief existence and wide distribution of periodically occurring Pa element morphotypes are explained by the phenomenon of evolutionary oscillations. This phenomenon implies that, at certain time periods in spatially separated populations of related species, their gene pools change simultaneously and in a similar way. The process of a synchronous increase in the frequency of a certain trait covers isolated and semi-isolated populations of related species in an area stretching hundreds and thousands of kilometers and almost simultaneously. A similar picture can be observed in the morphological transformations of conodonts at certain stratigraphic boundaries. Although the reasons for such evolutionary oscillations are still unclear, the established fact of their synchronous manifestation in large areas excludes the dependence of related populations on the abiotic conditions of specific locations. This circumstance represents another condition that makes it possible to consider the historical morphogenesis of Pa elements observed in the process of the described ensemble evolution of related conodont species as independent of abiotic causes and determined only by internal factors. Conclusion. Biochronological scales, which are based on the stages of evolutionary changes in a certain part of the skeleton, homologous to members of a long-existing group of organisms, are largely protected from the influence of abiotic conditions and can be considered as external scales.

Research subject. Microfauna of the Mikitovian Formation, Lower Carboniferous, Severny Island, Novaya Zemlya Archipelago. Mikitovian Formation is confined to the Severonovozemelskaya structural-facies zone. The section of the Goryakov Peninsula is a parastratotype of the Mikitovskaya Formation, characterized by a more carbonate composition of sedimentary rocks in contrast to the stratotype located on the Schmidt Peninsula. Aim. To clarify the age and to determine the boundaries of stratigraphic units based on a detailed study of foraminiferal communities in the Upper Tournaisian–Lower Visean terrigenous-carbonate deposits of the Mikitovian Formation. Materials and methods. Micropaleontological and microfacial studies of the collection of thin sections from the parastratotype of the Mikitovian Formation. Results. A foraminiferal sequence was revealed: the Spinoendothyra costifera Zone of the Kizelian Horizon and Eotextularia diversa–Dainella chomatica Zone of the Kosvian Horizon of the upper Tournaisian and the Eoparastaffella simplex Zone of the Pesterkovian Horizon and Viseidiscus primaevus Zone of the Ilychian Horizons of the Lower Visean, generally corresponding to the foraminiferal zonality of the General Stratigraphic Scale (GSS) of Russia. There are genera and species of foraminifera, characteristic of the eastern and northeastern regions of Russia, along with taxa widely distributed in the Urals and the East European Platform in microfaunal assemblages. The identified subdivisions are correlated with the zones and horizons of the western slope of the Urals. The dependence of the composition of the revealed microfaunistic complexes on their facies confinement is considered. Conclusions. The substantiated stratigraphic subdivisions of the Late Tournaisian–Early Visean interval make it possible to clarify the previously proposed regional schemes of Novaya Zemlya and to distinguish zones and horizons of the West Ural Subregion and the GSS of Russia instead of beds with fauna.