Home – Home – Jornals – Advanced Search

A dike of rock similar in composition to carbonatites has been found in the Aikhal diamondiferous pipe of the Alakit-Markha field of the Yakutian kimberlite province (YaKP). The fine-grained rock of essentially carbonate composition (dolomite and calcite) rich in thin-platy phlogopite contains minerals typical of carbonatites: monazite, baddeleyite, and pyrochlore. In the high content and distribution of incompatible elements the rock differs significantly from kimberlites and is transitional from kimberlites to carbonatites. The content of incompatible elements in this rock is 3-5 times lower than that in carbonatite breccias of the pipes in the Staraya Rechka kimberlite field of the YaKP (Nomokhtookh site). The compositions of accessory trace-element minerals from the Aikhal dike rock and the Nomokhtookh carbonatite breccias are compared. An assumption is made that the high contents of incompatible elements in the carbonatite-like rock, which caused the crystallization of accessory minerals, are due to the differentiation of kimberlite melt/fluid. The high Sr isotope ratios indicate that the rock altered during hydrothermal and metasomatic processes. The obtained data on the composition of the carbonatite-like rock cannot serve as an argument for the genetic relationship between the Aikhal kimberlites and typical carbonatites. The genetic relationship between kimberlites and carbonatites in the northern fields of the YaKP remains an open issue.

Based on new geochronological data on gabbroid and plagiogranitoid associations (Tavan Hayrhan, East Bayan Tsagaan, Bayan Tsagaan Uul, Tungalag, Three Hills, and Shutkhuin massifs) located among the Vendian island-arc volcanic complexes of the Lake Zone of Western Mongolia, an independent stage of Vendian island-arc intrusive magmatism (560-542 Ma) is substantiated. Geochronological ages determined for xenogenic zircon from Vendian gabbroids and granitoids (716-559 Ma) indicate a wide time interval of their formation and different natures of the sources. Several types of such sources are assumed. The source of the first type is rocks of the late Riphean oceanic crust of the Paleoasian Ocean, on which the Vendian island arc of the Lake Zone formed later. This is evidenced by the presence of xenogenic zircon with ages of ~716, 658-642, and 613-611 Ma. The source of the second (probably main) type is rocks of the Vendian island arc crust of the Lake Zone. This is indicated by the presence of xenogenic zircon with ages of 583-559 Ma, observed in all studied Vendian intrusive associations.

The Akhunovo-Petropavlovsk area of the Late Paleozoic granite magmatism is located in the northeast of the Magnitogorsk megazone (MMZ) in the South Urals. It is a series of successively intruded rocks (Petropavlovsk, Akhunovo, Karagai, and Uiskii Bor intrusions) differing not only in composition, the depth of formation, and ore content but also in the relationship with magmatic and fluid sources and in magma generation mechanisms. This area differs significantly in the number and composition of intrusive complexes from the igneous rocks and ore associations in the central and western parts of the MMZ. The granite magmatism pulses alternated with the collisional shearing/spreading and rifting stages. The Petropavlovsk mesoabyssal granite intrusion (347.0 ± 8.6 Ma) formed at the early stage of the area evolution. Its rocks are similar in composition to a suprasubductional series (melting products of a mantle source enrichednot only in water fluid but also in Cl). Later (310-306 Ma), at the collision-compression stage, crustal intrusion of the Akhunovo-Karagai granodiorite-granite complex took place. The intruded rocks are similar to the Middle Urals continental-margin gabbro-tonalite-granodiorite-granite plutons (320-290 Ma) bearing large gold-sulfide-quartz deposits (Berezovskoe etc.). At the final stage of the area evolution, during the transition from continental-margin regime to hard collision between the East European and Kazakhstan continents (late Carboniferous) and the intense shearing/spreading deformations, the Uiskii Bor granosyenite-granite intrusion (304.0 ± 4.8 Ma) rich in K and HFSE formed. Granite intrusions of this type have been revealed in the MMZ for the first time. Thus, the granitoid complexes of the Akhunovo-Petropavlovsk area formed under changes in geodynamic settings and are characterized by different compositions, depths of occurrence, and genesis. This permits us to consider the area a typical continental-margin center of the long-term mantle-crust interaction, where magma generation proceeded at different mantle and crust levels, with the participation of both suprasubductional and enriched plume-related rift sources.

The flow in the far turbulent wake behind a body of revolution is studied with the use of a three-parameter turbulence model, which includes differential equations of the turbulent energy balance, transport equation for the turbulent energy dissipation rate, and turbulent shear stress equation. Local equilibrium algebraic truncation of the transport equation for the turbulent shear stress yields the known Kolmogorov-Prandtl equation. Under a certain constraint on the values of the empirical constants and for the law of time scale growth consistent with the mathematical model, this equation is a differential constraint of the model or an invariant manifold in the phase space of the corresponding dynamic system. The equivalence of the local equilibrium approximation and the condition of the zero value of the Poisson bracket for the normalized turbulent diffusion coefficient and defect of the longitudinal component of velocity is demonstrated. Results of numerical experiments are reported; they are found to be in good agreement with theoretical predictions.

Laser ignition (λ = 1064 nm, τ_i = 120 ms) of the coal samples of different marks from the Kuznetsk coal basin was studied. Three consecutive stages of ignition were detected for all marks of coal. These stages are characterized by the threshold radiation energy densities H_cr⁽¹⁾, H_cr⁽²⁾, H_cr⁽³⁾ which are characteristic for each coal marks. It was established that the first stage involves surface heating and ignition of micro protrusions on coal particles. The duration of this stage does not exceed the time of the laser pulse. At the second stage, volatile matter are observed to evolve and ignite. The duration of combustion depends on the density of radiation energy. Ignition of the nonvolatile residue occurs at the third stage, upon reaching H_cr⁽³⁾; burning time is 40-150 ms. It was demonstrated that the threshold value at the first stage varies only slightly for all coal marks. For bituminous coal, the second threshold decreases with an increase in coalification degree, while the third threshold increases. The second and the third thresholds for lignite are comparable with the values of H_cr⁽²⁾ and H_cr⁽³⁾ for low metamorphic bituminous coals. Experimental results allow us to conclude that ignition occurs at the first and the third stages according to the heterogeneous mechanism, while at the second stage it occurs according to a homogeneous mechanism.

The prerequisites and modeling of possible outburst floods in the valley of the Bodomdara River (Tajikistan) are considered using detailed field data. According to the route survey results, Lake Bodomdara Upper is a supraglacial lake, which assumes possibility of its outburst leading to a cascade outburst flood. The depression of Lake Bodomdara Lower is relatively stable, and its outburst is possible without cascade flooding at anomalously high temperatures, upon snowmelt combined with extreme rainfall. Two probable scenarios are considered: (I) the outburst of Lake Bodomdara Lower (its volume comprised 328 000 m³ according to the bathymetric survey of 2020) and (II) the cascade outburst flood of Lake Bodomdara Upper (700 000 m³). Digital elevation model (DEM) ALOS PALSAR (12.5 m) and DEM based on images from an unmanned aerial vehicle for the Bodmodara River alluvial fan were used for predicting flood consequences. The outburst flood hydrographs for scenarios I and II were obtained using the lake outburst model developed by Yu.B. Vinogradov and an empirical formula, respectively. The material increment was estimated in the transport-shift model of mudflow formation. The resulting hydrograph was applied for zoning the Bodomdara and Shahdara river valleys with a total length of 75 km based on the FLO-2D model. According to the modeling, the maximum water discharge at the top of the alluvial cone of the Bodomdara River will reach 143 m³/s under scenario I and 348 m³/s under scenario II.

Many elements of the natural environment are areal objects that change their position and shape at all scales of variability. For sea ice, such elements can be fast ice, drifting ice, polynyas, ice massifs, boundaries of multi-year ice. In other earth sciences, these are the boundaries of glaciers, permafrost, snow cover, forest zone, various isolines of meteorological and oceanological fields (isotherms, isobars, etc.). To analyze such objects, approximations in the form of a grid area (rasterization) or a system of sections are usually used. In this article, we suggest a direct analysis of these objects based on operations with vector polygons. An efficient algorithm for calculating the probability (frequency of occurrence) of an unlimited number of polygons has been developed and tested. A criterion for selecting one of the real edges of a polygon as an analogue of the isoline of probability of intersections of polygons is proposed. The developed method has been tested using data on the fast ice of the Kara Sea taken from the digital ice charts developed by the Arctic and Antarctic Research Institute for 1998-2020. As a result, the maps of fast ice probability for the cold season of each year and for a given time of the year for the entire considered period have been obtained. Based on these data, the operational characteristics of fast ice have been estimated, and a tendency for a decrease in the area of fast ice during the considered period has been revealed. For the beginning of May (period of the maximum development of fast ice), analogues from factual observations characterizing extreme, median, and quartile probability isolines of fast ice occurrence have been found.

The results of studies of the methane content in the active layer and upper permafrost horizon in the areas of the Marre-Sale station (western Yamal Peninsula) and the Pechora River mouth are presented. Data on the methane content in Quaternary permafrost and ground ice of different geneses and data on methane emission from the surface of typical tundra in Marre-Sale are analyzed. The highest methane content in sediments of both the active layer and the upper permafrost is characteristic of boggy floodplains and waterlogged depressions on the surface of the marine terrace. In well-drained landscapes, methane is virtually absent in sediments of the active layer. In the upper permafrost, its content 5-6 times higher than in the overlying active layer. A large amount of methane (on average, about 2 mL/kg) is contained in loamy clay marine sediments at the base of the Marre-Sale section, as well as in the massive ice. The distribution of methane in permafrost and ground ice is close to a lognormal distribution. Significant methane flux (up to 10.7 mg/(m² ·h ) has been determined for highly moistened surfaces occupying about 45-50 % of the area of a typical tundra.

Conditions of the origin, existence, and melting of the superimposed ice are considered for Bellingshausen Ice Dome on Fildes Peninsula of King George (Waterloo) Island near Antarctic Peninsula. Every year, accumulation of superimposed ice on the ice dome reaches about 15 cm. In years with positive mass balance on the ice dome, the thickness of superimposed ice increases. The maximum measured thickness of perennial superimposed ice on the ice dome is equal 145-150 cm reaching 300 cm in some places. Significance of the superimposed ice in the ice mass balance of Bellingshausen Ice Dome in different years during the observation period from 2007 to 2021 is estimated. It is argued that regime field observations are necessary for finding seasonal boundary of the superimposed ice as the altitude of the equilibrium line.

Doctor of Geographical Sciences, chief researcher of the Laboratory of General Geocryology of the Melnikov Permafrost Institute, Siberian Branch of the Russian Academy of Sciences, Aleksey Aleksandrovich Galanin passed away on September 8, 2022. A well-known specialist in geomorphology, evolutionary geography, and paleogeographic reconstruction of periglacial landscapes of the northeast of Russia in Pleistocene and Holocene, Aleksey Galanin will be remembered as a talented researcher with lively mind, enthusiasm, and passion for science, a warm-hearted and wonderful person.