Research subject. Volcanogenic formations of the northern part of the Tagil megazone.

Material and methods. Volcanites of the Tagil paleo-island arc system and its frames were studied, including basalts and andesibasalts of the following formations: Khomas’inskaya O_1-2, Shemurskaya O₃-S₁, Pavdinskaya S1, Imennovskaya S_1-2, Turinskaya S₂-D₁, Perevozskaya D₁, Krasnotur’inskaya D₁, Limkinskaya D_2-3, as well as dolerites of the Ivdel complex D₃. Silicate (XFA) analyses and determination of rare elements by ICP-MS method were performed. The obtained data was analyzed using discrimination and spider diagrams, as well as indicator geochemical parameters.

Results. The geochemical parameters reflecting the degree of depletion of the host rocks of magmatic chambers, as well as the influence of fluids released during the dehydration of rocks of subducted slabs, quite definitely demonstrate an increase in the role of subducted material in the composition of island-arc magmas. This allows the onset of the subduction process, sharp changes in the conditions of its functioning and the time of its completion to be determined.

Conclusions. The obtained geochemical data confirms the existing concepts about the onset of the subduction process at the end of the Middle – beginning of the Upper Ordovician, restructuring (jumping?) of the subduction zone in the Lower Devonian and completion in the Upper Devonian.

Research subject. Upper Precambrian metaterrigenous deposits of the northern part of the Lyapinsky anticlinorium in the Subpolar Urals.

Material and methods. From the metaterrigenous rocks of the Upper Precambrian section of different stratigraphic levels, monofractions of zircons were isolated and their optical and isotope-geochronological (U-Pb LA-SF-ICPMS) studies were performed.

Results. Age boundaries of the formation of the Puivinskaya, Khobeinskaya, and Moroinskaya Formations in the Subpolar Urals were specified. A comparison was carried out of age populations of detrital zircons from metaterrigenous deposits of the Subpolar Urals and terrigenous sequences of adjacent regions similar in age. The age boundaries and the proposed location of crystalline complexes, the probable provenance areas of terrigenous material, were established.

Conclusions. The lower age limit of the formation of the basal layers of the Upper Precambrian of the Subpolar Urals does not go beyond the Late Riphean. The north-eastern periphery of the East European Platform, including the Subpolar Urals, in the Late Precambrian belonged to the same continental margin, and the accumulation of the Middle-North Timan and Subpolar Ural Upper Riphean sediments occurred in the common sedimentation basin. The lower age boundary of the formation of the Puivinskaya Formation (about 1000 Ma) determines the probable formation time of the Timan passive margin.

Research subject. Carbonate formations raised from depths up 1986 to 2973 m in the off-axis zone of the rift valley of the North Atlantic Ocean in areas of active young volcanism. The ocean floor here is composed of basaltoids and serpentinized gabbro-peridotites fragmentarily overlain by carbonate pelagic sediments.

Aim. To confirm the organogenic nature of these carbonate formations and to reveal new features of deep-water carbonate structures of this type.

Materials and methods. The research objects comprised 100 samples of branched and cone-shaped/crater-like carbonate formations, the primary studies of which were carried out directly on the research vessel. Analytical methods included optical microscopy, electron microscopy, X-ray fluorescence spectroscopy, X-ray diffractometry, infrared spectroscopy, inductively coupled plasma mass spectrometry, and isotope mass spectrometry.

Results. Among the most important features of the studied formations were found to be a concentric-zonal structure, which forms around the axial channel, and a thin dark brown crust of carbonate-ferromanganese composition. The abundance of planktonic fauna fossils and the distribution of mineralized biofilms with bacteriomorphic structures and glycocalyx were found in the body of crusts of the studied formations. More than 50 trace elements were found, including 11 essential (vital), 18 physiogenicallly-active and 22 antibiotic elements. The ratios of group contents of essential and antibiotic elements vary from 0.67 in the upper part of the structures to 0.001 in their lower part and up to 0.0006 in the volcanogenic substrate of the carbonate buildups. The ratio of the concentrations of essential zinc to physiogenically-active copper behaves similarly. In calcite, the isotopic composition of carbon, δ¹³С_PDB = = –0.16 ± 1.03‰, corresponds to marine sedimentary carbonates; conversely, while oxygen exhibits anomalously isotopically heavy values, δ¹⁸O_SMOW = 34.44 ± 3.21‰. In ferromanganese carbonates, the corresponding values are –3…1 and 32– 35‰.

Conclusions. The studied carbonate formations are solid solutions based on calcite in their body and based on siderite-rhodochrosite binary series in the composition of brown crusts. Specific features of the chemism and minal compatibility of carbonate solid solutions reflect the conditions of microbially-stimulated mineral formation. The conducted isotopic studies discovered the phenomenon of a combination of carbon and oxygen, fundamentally different in genetic nature, in the studied formations. For the explanation of this fact, a scheme for isotopic exchange of oxygen between marine bicarbonate and sulfate with the active participation of sulfate-reducing bacteria was proposed.

Research subject. The pre-Baikal submontane trough is located in the eastern part of the Irkutsk Amphitheater of the Siberian Platform, stretching for 600 km in a north-easterly direction. The trough started to form in the Mesozoic on the Paleozoic folded base and continued in the Cenozoic. The trough is characterized by a complex structure of shafts and deflections complicated by ruptures.

Aim. To investigate the insufficiently studied ruptures of the platform cover, which are difficult to map due to minor displacements of their wings.

Materials and methods. The method of specialized mapping of crustal fault zones based on a analysis genetically related of ruptures families was used. A network of 18 points of geological and structural observations in rocks of different ages of the sedimentary cover was created.

Results. A rank structural-genetic analysis of fractures mapped in rocks of different ages and composition revealed specific features associated with the gradual development of the trough. The ruptures identified in the rocks of the pre-Cenozoic cover of the platform satisfy the parageneses of the compression zone, the dextral strike-slip zone and the extension zone of the north-eastern strike. Deformations in Cenozoic sediments belong to the parageneses of dextral strike-slip zone and the extension zone. These parageneses consist of strike-slip and normal faults.

Conclusions. The Cenozoic Pre-Baikal submontane trough was formed under strike-slip and extension conditions. The compression stage is highlighted in the Pre-Cenozoic base.

Research subject. Cenozoic stratified sedimentary formations exposed by well 517 in the Uro area.

Aim. To study a section of spatially combined deposits from the Selenga-Vitim Downwarp and Baikal Rift Zone.

Methods. Lithological and stratigraphic analysis, lithogeochemical, paleontological studies.

Results. Oligocene deposits of the Kularikta Formation from the Selenga-Vitim Downwarp found for the first time, unconformably overlain by deposits of the Baikal-type basins of the Baikal Rift Zone (Miocene-Lower Pliocene Tankhoi Formation, Upper Pliocene-Eopleistocene Anosov Formation, and Quaternary polyfacies stratum). Four palynocomplexes are characteristic of the section: PC I of the Early Oligocene shows mixed forests of spruce, pine, hemlock with an admixture of alder, birch, and broad-leaved deciduous trees with an insignificant participation of evergreens that existed in a warm temperate climate; PC II of the Late Oligocene reflects expansion of areas of coniferous vegetation in the transition to a moderate climate; PC III of the Early Miocene demonstrates mesophilic coniferous forests and a significant role of broad-leaved tree species in warmer and more humid climatic conditions; PC IV of the Late Miocene–Early Pliocene displays vegetation close to taiga with rare relics of coniferous and deciduous plants under conditions of increasing cooling with a decrease in total moisture supply. A lack of pollen grains in the transitional deposits from the Kularikta to the Tankhoi Formation of the late Oligocene–early Miocene corresponds to conditions of a paleoclimatic pessimum. A member of lacustrine sediments with diatoms was found in the Tankhoi Formation, 50 species of diatoms are identified, among which the planktonic species Alveolophora antiqua is absolutely dominant in a paleowater body of significant depths and a large volume of water mass.

Conclusion. The Uro section combines the Oligocene deposits of the Selenga-Vitim Downwarp and Miocene-Quaternary deposits of the Baikal Rift Zone.

Research subject. Upper Tournaisian clayey-siliceous-carbonate deposits of the Malaya Usa section (Polar Urals).

Material and methods. The composition and structure of the deposits (50 samples, 51 thin sections) of the section were considered to determine the conditions of sedimentation; 13 samples were chemically disintegrated in 7–10% solution of acetic acid, and thin sections were studied for biostratigraphic analysis (conodonts, ostracods, and foraminifers); the carbon and oxygen isotopic composition of carbonate deposits (49 samples) were analyzed. A three-stage screening test of samples for isotopic-studies was carried out.

Results. The Malaya Usa section comprises mainly micritic limestones with fossils silicified to various degree (wackstone to packstone). The features and composition of the sediments indicate sedimentation in low dynamic conditions below the wave base. Biostratigraphic analysis is based on the identification of foraminifers, as well as a few conodonts and ostracods. Foraminifers characterize the Eotextularia diversa–Dainella chomatica Zone, which is approximately comparable to the Upper typicus–anchoralis–latus conodont zonal interval and Entomoprimitia malinovkaensis‑Marginia tschigovae ostracode zones of the top of the Tournaisian. The isotope-geochemical data obtained from the section demonstrate a general lightening trend in the isotopic composition of δ13Ccarb up the section. This trend, along with the biostratigraphic data, mades it possible to compare the δ13Ccarb sequence of the Malaya Usa section with sequences from a number of geographically separated sections of the world (Belgium, South China, USA), which are considered as the Tournaisian isotope carbon event (TICE).

Conclusions. The deposits of the studied section were probably formed under the conditions of a very gentle slope (ramp), where the material accumulated at the foot as a filling sequence in the southern part of the Korotaikha intrashelf paleodepression. Using the Malaya Usa section as an example, it is shown that not only the peak positive deviations of the TICE in the upper part of the isosticha Zone and in the lower part of the typicus Zone, but also the isotopic structure of the upper Tournaisian has a significant correlation potential. The use of the isotope-geochemical method as an auxiliary application to biostratigraphy made it possible to improve the age determination of the section from the interval of the Upper typicus–anchoralis–latus conodont zonal interval to the Upper typicus Zone of the standard conodont zonation.

Research subject. The possible influence of the SiO₂ environment as the most common component of the mantle on the deep abiogenic synthesis of hydrocarbons in the CaCO₃–FeO–H₂O and Fe₃C–H₂O systems under thermobaric conditions corresponding to those in the upper mantle is investigated.

Materials and methods. Experiments were carried out using a high-pressure unit in Toroid-type chambers across the thermobaric range of 2.0–4.0 GPa and 220–750°C. CaCO₃ and Fe₃C were used as carbon donors, H₂O was used as a hydrogen donor, and SiO2 was used as an environment. The synthesized products were analyzed by gas chromatography and X-ray diffraction.

Results. Across the entire temperature and pressure range used, mixtures of light alkanes with the predominance of methane were obtained. The composition of the hydrocarbon systems synthesized in the presence of SiO₂ was similar to that obtained at the same thermobaric parameters without SiO₂, depending exclusively on the temperature and pressure of synthesis. The conducted X-ray diffraction analysis of solid products demonstrated transformation of quartz into coesite at 400°C and 750°C.

Conclusions. According to the conducted investigation, the qualitative and quantitative composition of hydrocarbon systems formed during the abiogenic synthesis of hydrocarbons in the presence of SiO₂ corresponds to the results of similar experiments without SiO₂. However, the total yield of the hydrocarbon systems in the SiO₂ environment decreases. The dependence of the composition of the synthesized hydrocarbon systems on the thermobaric conditions of synthesis remains in the SiO₂ environment.

Research subject. The horizons of ferruginous sedimentary rocks in the massive sulfide deposits of the Urals.

Aim. To estimate the Ti behavior upon halmyrolytic transformation and lithogenesis of calcareous hyaloclastites and carbonatesulfide-hyaloclastite sediments.

Materials and methods. Microtextures of authigenic aggregates of Ti minerals (anatase, rutile, titanite) in jasperites and gossanites of various Urals massive sulfide deposits were studied. The minerals were identified using microscopic and electron microscopic methods, as well as electron back-scattered diffraction.

Results. Upon partial halmyrolysis of calcareous hyaloclastites, Ti was removed with the formation of authigenic anatase rims around hematitized hyaloclasts. The full transformation of hyaloclastites to hematite-quartz jasperites resulted in decomposition of authigenic Ti minerals. Authigenic rutile and titanite formed in gossanites (hematite-quartz and hematite-chlorite products of submarine oxidation of calcareous sulfide-hyaloclastite sediments). The occurrence of abundant bacteriomorphic structures in corroded hyaloclasts indicates a significant role of bacteria in halmyrolysis.

Conclusions. Titanium for the formation of Ti minerals in ferruginous sediments was sourced from hyaloclastites. The halmyrolysis of calcareous hyaloclastite sediments and related formation of jasperites occurred under alkaline conditions favorable for the transportation of Ti in the form of hydroxycarbonate complexes. The formation of rutile instead of anatase was associated with lower pH values (<5) due to oxidation of pyrite in sulfide-bearing hyaloclastite sediments. Titanite formed as a result of further alteration of Ti-bearing phases. Our results solve the fundamental problem of Ti mobility during halmyrolysis of hyaloclastites, which contradicts its commonly accepted immobility in hydrothermal processes.

Research subject. Quartz veins of the Svetlorechenskoye, Karayan, Gora Khrustalnaya and Tolstikha quartz deposits in the Southern Urals.

Methods. An optical study of quartz was performed using an Olympus BX51 optical microscope. A fluid inclusion study was performed using a thermostage TMS-600 (Linkam) equipped with the LinkSys V-2.39 software and an Olympus BX51 optical microscope (South Urals State University, Miass). The fluid composition in the inclusions was estimated from eutectic temperatures. Fluid salinity was calculated based on the melting temperatures of crystalline pha ses. Registration of infrared spectra was carried out using an infrared Fourier spectrometer Nicolet-6700 Thermo Scientific (SU FRC MG UB RAS, Miass). The spectra were processed using the OMNIC Thermo Nicolet software package and the Peakfit program. The extinction coefficients for calculating the concentration of molecular water and OH-groups were used from.

Results. The veins are composed of coarse-grained milky-white quartz. The fluid inclusion data shows that the quartz veins were deposited from similar in composition NaCl-H₂O fluids with salinities of 3–9 wt % NaCl eq. and at temperatures ranging from 100 to 280°C. Quartz in the Tolstikha deposit was deposited at the highest temperatures. According to IR spectroscopy data, quartz in the studied deposits is characterized by high contents of molecular water and average concentrations of Al-OH groups. According to the content of OH-groups, quartz in the Tolstikha deposit approaches industrial granulated quartz used in the production of high-purity quartz concentrates.

Conclusions. Quartz veins in the studied deposits formed at temperatures ranging from 100 to 280°C. The salinity of inclusions in quartz ranged from 10 to 3.5 wt % NaCl eq. Mineral-forming fluids were of Na-chloride or Na-K-chloride composition, which indicates quartz crystallization during the post-diagenetic (metamorphic) transformation of rocks. Quartz in the studied deposits is characterized by a specific ratio of water and Al-OH, which is associated with the conditions of deposit formation and incompleteness of quartz metamorphism processes therein.

Aim. To carry out a retrospective forecast of the eight strongest earthquakes (with a magnitude greater than 8) of the 21st century using the Load/Upload Response Ratio (LURR) method.

Methods. Calculations were performed according to the authors’ original data processing technique, which had been successfully tested while studying the seismicity of Sakhalin Island. A significant advantage of this methodology consists in using fixed (basic) parameters of mathematical processing and sampling of calculated earthquakes (geometry of the calculation area and sequestration by magnitude). This enables researchers to conduct not only retrospective studies, but also real-time forecasting. In the present paper, a seismic catalog of the United States Geological Survey (USGS) was used.

Results. For four of the considered earthquakes, precursors in the form of anomalies of the LURR parameter were identified. These anomalies had manifested themselves in periods from six months to two years before the earthquake, which is consistent with our results for Sakhalin. At the same time, no other anomalies (false alarms) were recorded in three cases. For the other four earthquakes, no anomalies were recorded at all. It is noted that the level of seismic activity (in the operating range of magnitudes) in these cases allows the smoothing window to be reduced. In some cases, the calculation for a window twice as small (180 days) revealed pre cursors, at the same time as contributing to the appearance of additional, false anomalies.

Conclusions. It was confirmed that the authors’ methodology for data preparation and calculation parameters selection, as well as the LURR method, apparently have limited possibilities for extrapolating to various seismically active regions of the planet. There may be different reasons, which have not been considered in the present paper due to the uncertainty associated with the capabilities of the USGS network.