Vol 482, No 1 (2018)

Analysis of the morphology of the recent uplifts on Precambrian cratons and geological–geophysical data on the structure of the crust and mantle indicate that these structures were formed due to expansion of the crustal rocks as a result of retrograde metamorphism. This occurred due to the contribution of large volumes of deep fluids to the complexes of the Early Proterozoic rocks, which underwent high-grade metamorphism in the lower crust. Later, these complexes were moved to the shallower depths after denudation of thick overlap sequences from the craton’s surfaces. The calculation of the volumetric expansion effects using P–T diagrams for the main types of metamorphic rocks shows that this mechanism could have prompted the uplifts of the Precambrian crust in recent time with amplitudes from 100–200 to 1000–1500 m.

New paleomagnetic data on Devonian and Lower Carboniferous rocks of the Magnitogorsk Zone (Southern Urals) are presented. The paleomagnetic pole calculated for the Lower–Middle Devonian is quite close to the coeval pole of the Baltica Paleocontinent (Laurussia), which indicates that the Magnitogorsk island arc was probably located close to the continent, but not being accreted with it. Paleomagnetic data obtained for Lower Carboniferous rocks may indicate that the Magnitogorsk island arc was turned in the Early Carboniferous and collided with the continent of Laurussia forming a single continent.

Fundamentally new data on the structure of the Nizhne-Koshelevskoe vapor-dominated geothermal deposit (South Kamchatka) were obtained. An isometric area of intensely argillized rocks saturated with a vapor–gas mixture with the shape of an irregular cup occurring up to a depth of 250–300 m was distinguished in the central part of the deposit beneath the major zone of hydrotherm discharge. This area is controlled by a heat source through a subvertical channel of increased fracture–porous permeability for a vapor–gas fluid with a thickness of 300–350 m and a depth of >5 km. The elements of the paleohydrothermal system, such as relatively rock blocks composed of propylite and secondary quartzite with epithermal ore mineralization, were distinguished at the core of the deposit. The heat was transferred by the crustal flux of reduced hydrocarbon fluid.

The heterogeneous assemblage of zircons was identified in metamorphic schists of the Karabash site of the West Siberian Plate. Based on the U–Pb (SHRIMP II) isotope data, zircon varies in age from the Archean–Paleoproterozoic boundary to the early Permian. The Precambrian age data obtained for the study area reflect the erosion of the Precambrian complexes in the framework of West Siberian Plate (with subsequent redeposition of the ancient detrital material within the West Siberian megabasin). Our results make it possible to clarify the history of the formation and evolution of metamorphic rocks in the basement of the West Siberian Plate.

The geochemical study of the suspended matter in the waters of the Amazon River and its tributaries revealed that the chemical composition of this material ranges widely; however, generally, it is similar to the average composition of the suspended matter in the rivers and clayey sedimentary rocks around the world. Against this background, an essential regional Hg enrichment due to the anthropogenic factor is distinguished. The suspensions from the so-called clear waters from the tributaries of the Amazon River—Xingu and Trombetas—demonstrate the local enrichment in Pb, Sn, Zn, and organic carbon indicating the ore mineralization of the drainage basin, and points to the presence of metal-organic complexes.

The Sr isotope composition in glendonites from two sections of the Middle Jurassic of Northern Siberia has been determined for the first time. Glendonite was formed by the replacement of icite by calcite during diagenesis. The ⁸⁷Sr/⁸⁶Sr in most of the samples of glendonites (0.70687–0.70715) is insignificantly lower than this ratio in the Late Bathonian–Early Bajocian ocean. This may indicate a contribution from the Callovian seawater in the formation of individual calcite generations or the influence of methanogenic fluid of deep origin.

New data on the mineral composition of the Severny Kolchim meteorite, found in Perm Region in 1965, are presented. It has been found that that the meteorite matter is composed of olivine (chrysolite), orthopyroxene (bronzite), clinopyroxene (diopside), plagioclase (oligoclase, bytownite), glass, chromite, magnetite, ilmenite, rutile, metals Fe and Ni (kamasite, taenite, tetrataenite), copper, sulfides (troilite, pentlandite, covellite), chlorapatite, and merrillite. Diopside, tetrataenite, chlorapatite, and merrillite were identified in the Severny Kolchim meteorite for the first time. The chemical compositions are given for all these minerals. The meteorite itself is a nonequilibrium ordinary chondrite stone belonging to petrological type H3.

The experimental results of natural pyrochlore behavior in KF solutions in the presence of quartz at 550–850°C and 50–100 MPa are presented. It is shown that silicate matter (quartz) exerts a significant effect on pyrochlore solubility in aqueous solutions of fluorides of alkaline metals under hydrothermal conditions. This study of the fluid inclusions has revealed the occurrence of reactions of high-temperature hydrolysis of KF under the experimental conditions: KF + H₂O = KOH + HF; in which case, the interaction with quartz SiO₂ + 2KOH = K₂SiO₃ + H₂O is followed by the formation of a silicate glass phase (an aqueous solution–melt). This phase of alkaline glass is a Nb concentrator (Nb₂O₅ up to 16 wt %). The coefficient of Nb distribution between the glass and the fluid is ≈500 (in favor of the glass). It is determined that the phase of the silicate solution–melt can serve as an effective concentrator of the ore component (Nb) at the last lowtemperature stages of crystallization of rare-metal granites.

The first chromatography–mass spectroscopy data on volatiles in diamonds synthesized in the Fe–S–C system with 5 wt % S at 1400–1450°C and 5.0–5.5 GPa indicate the evolution of volatile composition during the diamond growth and, correspondingly, the variation in redox conditions of the reaction cell. A significant role is played by various hydrocarbons (HCs) and their derivatives, the content of which can reach 87%. Our data on possible abiogenic synthesis of HCs (components of natural gas and oil) can result in global recalculations (including climate) related to the global C cycle.

We have performed physical modeling of stick-slip on a large fault in the elastic-viscous-plastic model. It was found that, after each full activation, slips on the fault took place on its particular segments and evolved with time in a regular manner. This evolution is divided into the regressive and progressive phases. In the former phase, against the background of stress relaxation, the segment structure of the fault gradually disappears owing to the directed partitioning of larger segments into smaller ones, with some of them attaining a passive state. With the onset of the progressive phase, the decrease in stresses changes to increase. As stresses increase, some active segments reach a critical density and then decrease owing to the growth of smaller segments and their merging to form larger ones. The mean and total lengths of the recurrence graph, as well as its angle (β-value), increase as this process evolves.

This paper reports the estimated scales of optically dense haze over Eurasia for the period from July 15 to July 31, 2016, including the Siberian smoky haze (with a smoke area of 16.3 million km²) over Siberia and European Russia, and also many countries of Europe, Kazakhstan, and other countries of Asia, the human-induced smog over the North Chinese Plain (about 2 million km²), dusty haze in the Takla-Makan Desert (about 0.8 million km²), and haze over India and Pakistan (approximately 1 million km²).

On the basis of the Laplasian theory of capillarity, laws of continuous media mechanics, and concepts of physical-chemical mechanics of heterogeneous substances, the mechanism of emulsion formation during immiscible fluid flow in rocks is given. It is shown that this mechanism does not depend on the choice of the porous medium model in certain limits, but is determined by stresses acting on the meniscus and by the presence of slow-moving fluid films on the pore surface. The obtained expression for the minimal radius of capillaries where emulsion can form, combined with relevant experimental results, suggests that setting of the pressure gradient can either trigger or prevent emulsification.

Original scientific approaches to the assessment of spatial and temporal variability of biota of Lake Onego, which may be used as a basis for its biomonitoring, are proposed for the first time. Reliably differing natural phenological phases of the seasonal cycle of plankton of Lake Onego have been revealed. The terms, duration, and interannual variability of phases are the criteria of reaction of the planktonic system to climatic changes. A series of models for assessment of the functioning stability of the ecosystem was developed on the basis of the regression method of minimization of orthogonal distances. Biotic indexes elaborated on the basis of the benthos structure were used for zoning of the bottom of Lake Onego. Three zones—of anthropogenic impact, intensive development of amphipods, and effect of geochemical anomalies—are specified. The proposed approaches may be applied in monitoring the status of large lakes in the boreal zone.

The velocity and structure of the Lomonosov Equatorial Undercurrent of the Atlantic Ocean are determined based on the data measured with a shipborne acoustic profiler from 2014 to 2017. The seasonal variability of this flow is estimated, and the cases of its outcropping to the surface in the spring of the Northern Hemisphere are revealed.

The features of the spatial structure of coastal water caused by the impact of a nonstationary deep source of waste under stratified conditions is studied using a numerical hydrothermal model. The task is solved for the case of contaminated water outfall in Golubaya Bay of the city of Sevastopol. It is found that the activity of the source is accompanied by a jet and a stream of contaminated water. The pycnocline layer is mostly polluted with the contaminated area reaching 0.3–0.5 km². The increase in the vertical shift of the velocity of background current leads to the increase in the existing period of contaminated zones and displacement of the stream of waste water toward the free surface (the stream becomes more localized vertically). The fields of contamination, temperature, and salinity of water have a complex spatial structure.

The design features of an oceanological video-monitoring system created for operational research of coastal infrasonic wave processes are described. The results obtained confirm great opportunities for its use in fundamental and applied works in various seasons. The processing of the obtained experimental data has revealed the dynamics of the wave processes starting from wind waves to diurnal tides.