Volume 484, Nº 2 (2019)

The results of U–Th–Pb geochronological study indicate that the youngest peaks on the relative probability curves of the age obtained for the Un’ya-Bom terrane correspond to ages of 207 and 212 Ma. These values were obtained for zircons from the meta-aleurolite samples from the Kurnal and Amkan formations, respectively. Similar age estimates for the youngest peaks were also obtained in the case of detrital zircons from the metasedimentary rocks of the Tukuringra terrane in the eastern part of the Mongol–Okhotsk fold belt, which indicates that, within the belt, Lower Mesozoic flyshoid complexes are much more widespread than was assumed. Based on the geochronological and Sm–Nd isotopic data obtained, it was shown that the material was carried to the sedimentation basin mainly from the continental massifs of the Amur superterrane.

Data on the Early Jurassic volcanic rocks of the Kobyumé graben system, which formed at the Verkhoyansk passive margin of the Siberian Craton, are presented. The volcanic complex contains products of basaltic eruptions that occurred under conditions of a shallow sea. The basalts have elevated TiO₂ contents (>1.8 wt%), and variations of their composition were controlled by fractionation processes. By their geochemical characteristics, the volcanic rocks are transitional between ocean island basalts and enriched basalts of mid-oceanic ridges. Taking into account the remote location of the Kobyumé graben region from the convergent boundaries of lithospheric plates and from the nearest areas of contemporaneous magmatism, the data obtained support the conclusion that the Kobyumé tectono-magmatic areal is a result of a small mantle plume effect onto the passive margin of the Siberian continent.

Typical features of platinum group minerals (PGMs) and the results of ¹⁹⁰Pt–⁴He dating of the Fe–Pt solid solutions are presented for complex gold–platinum–diamond placers with unidentified sources of the Anabar River basin. For the first time, the ¹⁹⁰Pt–⁴He isotopic system is used for determination of the possible age of the primary source of a PGM placer from the example of ferroan platinum with a disordered structure along with isoferroan platinum. The PGMs of these placers mostly include ferroan platinum and isoferroan platinum and rare Ru–Ir–Os alloys. The calculated bulk composition of the silicate inclusion of Ir platinum corresponds to the rocks of the ijolite–melteigite series. The ¹⁹⁰Pt–⁴He age of the Fe–Pt solid solution grains is 261 ± 13 Ma. Thus, our data indicate the relation between placer PGMs of the Anabar River basin and Permian–Triassic complexes of alkaline–ultramafic rocks.

The Sr isotope characteristic of carbonate rocks in the Central Azov Group has been reported (0.70322–0.70352), the Nd model age of silicate sediments has been calculated (2.34–2.31 Ga), and the U–Pb age of trondhjemites (2052 ± 5 Ma) breaking through carbonates was determined. According to the data obtained, the marine sedimentary cover of the Azov block making up the Early Precambrian Sarmatia Continent was formed in the Early Paleoproterozoic 2.23–2.34 Ga ago.

The results of studies indicate that the age of the protoliths of garnet-bearing biotite–sericite–muscovite schists of the Inim Block is <991 Ma, and they are derived from rocks of the Neo-, Meso-, and Paleoproterozoic (as well as Archean) crust. This suggests that the Inim Block is exotic relatively to the Argun Superterrane due to the formation of the protolith of its metasedimentary rocks largely from erosion products of the Early Precambrian continental crust, the presence of which within the Argun Superterrane is not proven. It is not excluded that the Inim Block is a fragment of the Dzhugdzhur–Stanovoi Superterrane implanted in the structure of the Argun Superterrane as a result of Mesozoic tectonic events.

The experience of applying the laser ablation technique to study the sulfur isotopic compositions of pyrite and arsenopyrite samples from gold deposits of the Baikal–Patom highland is discussed. The experimental procedure is described. All studied samples were found to display δ³⁴S and δ³³S values in strict compliance with the law of mass-dependent sulfur isotope fractionation. Regular lightening of the sulfur isotope composition in the course of crystal growth for pyrites from the Sukhoi Log deposit and the isotopic homogeneity of pyrite and pyrrhotite from the Golets Vysochaishii deposit were established. The conclusion that the sulfur isotopic homogeneity of sulfides in the ores occurs probably owing to metamorphism within the Mama–Oron belt was made.

New results of U–Pb zircon and Nd–isotope analyses of the Goryachinskiy Pluton adakite granites have been obtained. The pluton is exposed along the Baikal coast in the section where a section of sheared tectonic sheets of the Baikal–Muya Belt wedges out. The determined Early Cambrian (545 ± 6 Ma) age of the granitoids is unusual in the Northern Baikal region. These new geological and isotopic data are interpreted as an indication of the formation of the granitoids studied at the final stage of the Late Baikal strike–slip tectonics, which caused the pulse of the adakite magmatism within the Baikal–Muya belt.

The melt in the alumosilicate (granite) melt–molten fluoride salt system is experimentally studied at Т = 800–1200°С and Р = 1–2 kbar. The data on the phase composition of silicate–salt systems and the character of the phase distribution of ore components are presented. The coefficients of the distribution of rare-earth elements (REEs) between the granite melt and the fluoride phase at 900–1200°С and Р = 1–2 kbar are obtained. It is shown that the REEs enrich the fluoride phase relative to the silicate melt. The elements of the (V, Nb, Ta) and (Ti, Zr, Hf) groups almost always prefer a silicate melt to a fluoride melt.

Experimental data are presented to show that the spatial and temporal variability of the composition of river waters cannot be explained solely by the influence of sources and effluents of the substances and that there are additional significant factors that support or even initiate the dispersion of the concentration of pollutants here. This variation is reflected in the resources and the economic characteristics of the rivers; so identification of its reason is important. Thus, the hydrodynamic structure of the water flow is studied by analyzing the complete system of equations of fluid motion mechanics. The completed work allowed us to show that the elements of this structure are waves, vortices, and highly gradient layers (ligaments), presumably creating the described dispersion effect. Further investigation of the relationship of the precise hydrodynamic and hydrochemical structures of river waters will contribute to better understanding of the water-environmental processes, ensuring the perfection of water management methods.

The geometry of supposed coupling zones in the Kamchatka subduction zone is determined by the earthquake size distribution based on ealier revealed relationship between its shape and rate of inelastic deformations. In the areas of higher aseismic slip, a break of linearity in earthquake size distribution is observed owing to the deficit of large earthquakes. Zones of higher coupling between the oceanic and continental plates are characterized by an excess of large earthquakes and an inverse bend in the earthquake size distribution. The mapping results of the bend value agree with the coupling zones distinguished from satellite geodetic data and inversion of marigrams.

A comprehensive analysis of waveforms of seismic and infrasonic vibrations from the earthquake that occurred on December 5, 2014, in the water area of Lake Hovsgol was performed. The analysis showed that the infrasonic signal recorded at the Tory station (Geophysical Observatory of the Institute of Solar-Terrestrial Physics, Russian Academy of Sciences) was formed by the sources of three generation types: local, secondary, and epicentral. The obtained results gave support to the model of epicentral infrasonic signal generation by flexural waves from an elastic ice membrane on the surface of Lake Hovsgol.

This paper reports the results of the third Russian–Vietnamese expedition (V.I. Il'ichev Pacific Oceanological Institute, Far East Branch, Russian Academy of Sciences and the Institute of Marine Geology and Geophysics, Vietnam Academy of Science and Technology) in the Gulf of Tonkin, South China Sea (April 2016). The studies revealed new specific features of the distribution and origin of gasgeochemical fields in sediments within the rift zone of the Red River along a 150-km profile. Four zones with high-amplitude anomalies of hydrocarbon gases, helium, hydrogen, carbon dioxide, and carbon monoxide were revealed. The distribution of the anomalies reflects the tectonic structure of the area and points to the presence of several lithospheric sources of gases including gases of deep origin. The studies were carried out within the scope of the Joint Vietnamese–Russian Laboratory for Marine Geoscience (V.I. Il'ichev Pacific Oceanological Institute, Far East Branch, Russian Academy of Sciences and the Institute of Marine Geology and Geophysics, Vietnam Academy of Science and Technology).

The features of vortical suppression of tsunami waves by an impermeable underwater barrier have been studied. The height of the barrier is close to the optimum corresponding to the maximum effect of vortical suppression of the wave energy.

Large-scale atmosphere–ocean interaction in the Atlantic sector of the Arctic Ocean is analyzed. New studies demonstrate that the variability of Atlantic water inflow into Nordic seas is driven largely by the leading mode of year-to-year variations in the ocean–atmosphere system—the North Atlantic oscillation (NAO). A new vision of the effect of the NAO on the hydrophysical characteristics of the Norwegian and Barents seas is offered.