Home – Home – Jornals – Advanced Search

Chemical, radioisotopic, and palynological studies of the bottom sediments of mesotrophic Lake Arakhlei have been carried out for paleoclimatic reconstructions and estimation of the sedimentation rate.

The paper is focused on recent displacement rates in the Altai-Sayan region, obtained by hydroleveling, leveling, and satellite geodesy. Effective elastic moduli and viscosity parameters of the crust are used in the modeling of coseismic and tectonic processes. The elastic moduli are determined from measurements of periodic vertical displacements during seasonal loadings of the Sayano-Shushenskaya hydropower plant. We present the results of the modeling of coseismic displacements during the earthquakes of 10 February 2011 (M = 6.1) and 27 December 2011 (M = 6.7) in Tuva and West Sayan. The results of GPS determinations for postseismic displacements in the Chuya earthquake zone (Gorny Altai, 27 September 2003, M = 7.5) are analyzed; models for the geologic medium are selected; and its effective viscosity is estimated. The tectonic component of the recent crustal displacements in the Altai-Sayan region is defined.

A 450 km long composite crustal section of the Urals folded system at 67º N and 60–90° E has been compiled from seismic data on the Polar Urals transect and the results of targeted studies. The main elements of the subsurface structure at more southerly latitudes are preserved for this cross section. The general deep–seated structure is divided into the western and eastern branches. The western one has a northwestern trend and corresponds to the West Urals megazone. The eastern one, with a northeastern trend, includes the Central Urals and East Urals megazones.

A thermomagnetic analysis has been performed for 737 picroilmenite samples from the cores of eight boreholes in the N–S–striking drilling profile of the Zarnitsa kimberlite pipe in the Daldyn kimberlite field, Yakutia. Based on the shapes of thermomagnetic curves and the Curie points, 29 samples were chosen for detailed microprobe studies of chemical composition and elucidation of the dependence of their thermomagnetic parameters on the content of the hematite end-member in the picroilmenites. The thermomagnetic curves of most of the studied picroilmenite samples are approximated by a two-component model for the hematite end–member distribution: the main and supplementary distribution. The average hematite end-member content in the main distribution coincides with the probe microanalysis data and is always lower than the average content in the supplementary distribution. The relative hematite end–member contents in the main and supplementary distributions within the picroilmenite grains are indicators of the dynamics of the mineral formation in different parts of the Zarnitsa pipe. The data obtained testify to the multistage formation of the pipe under unstable thermodynamic conditions, which explains the intricate distribution pattern of picroilmenite.

The paper describes the effects of the passage of the Chelyabinsk meteoroid (exploded on 15 February 2013 over the Chelyabinsk Region), which were established from geophysical data from West Siberian stations. The trajectory and speed of the meteoric body from the start of the glow to the breakup were recorded by surveillance cameras and dashcams. Records from broadband seismic stations were used to determine the exact time of the explosion (03:20:34 UTC) from the arrival times of the surface wave produced by this event. The explosion energy was estimated from the surface-wave amplitudes at ~100 ktons on the assumption that the wave originated from a point source similar to a high–altitude thermonuclear explosion. A database of records from seismic stations obtained during the meteoroid passage has been compiled.

We consider the primary nature and sources of the protoliths of metamorphic rocks of the Kurai block located in the large Teletskoe-Kurai system of deep faults separating the Gorny Altai and West Sayan structures. It has been established that the protoliths of the Kurai block metapelites were deposits of transitional crust: They lack typical rocks of mature continental crust (arkoses, litharenites) and have reduced (relative to the upper continental crust) contents of lithophile elements and elevated contents of transitional elements. The average Nd model age of the protoliths of the metapelites of the Kurai complex corresponds to the Middle Riphean (1.4–1.6 Ga). The metabasites of the Kurai complex are similar in petrologic composition to metamorphic products of oceanic basalts. It is shown that the formation of metamorphic associations of the Kurai block was caused by tectonometamorphic transformations of a compositionally heterogeneous rock unit (basalts, aluminous and volcanomict sediments), which were, most likely, a fragment of Middle Cambrian–Early Ordovician turbidite basin with an oceanic basement.

Distribution of water among the main rock-forming nominally anhydrous minerals of mantle xenoliths of peridotitic and eclogitic parageneses from the Udachnaya kimberlite pipe, Yakutia, has been studied by IR spectroscopy. The spectra of all minerals exhibit vibrations attributed to hydroxyl structural defects. The content of H₂O (ppm) in minerals of peridotites is as follows: 23–75 in olivine, 52–317 in orthopyroxene, 29–126 in clinopyroxene, and 0–95 in garnet. In eclogites, garnet contains up to 833 ppm H₂O, and clinopyroxene, up to 1898 ppm (~0.19 wt.%). The obtained data and the results of previous studies of minerals of mantle xenoliths show wide variations in H₂O contents both within different kimberlite provinces and within the Udachnaya kimberlite pipe. Judging from the volume ratios of mineral phases in the studied xenoliths, the water content varies over narrow ranges of values, 38–126 ppm. At the same time, the water content in the studied eclogite xenoliths is much higher and varies widely, 391–1112 ppm.

Gravity models of the crust and upper mantle to a depth of 100 km are analyzed to study structural relationships of tectonic and tectonophysical media of different rigidities with the distribution of shallow ore deposits above the Aldan–Zeya plume. The spatial correlation of ore clusters and districts with high crustal viscosity inhomogeneities at depths of 10, 20, and 35 km shows distinct stepwise behavior. On the other hand, media of decreased viscosity are observed in the lower crust (at depths of 25–30 km), subcrustal (40–50 km) layers, and asthenosphere (at a depth below 70 km). They are related to chambers of the complete or partial melting (heat sources) of magmatic and ore occurrences near the Earth’s surface. Lateral metallogenic zoning in the spatial distribution of the ore deposits is due to the spread and redistribution of magmas and ore-forming fluids, shielded by rigid plates in the lower crust. A naturally determined series of ore parageneses is observed from center to flanks of the plume: Au, Mo → Au, Ag, Pb, Zn → Au, Pb, Zn → Au, W → Au, Sb → W, Sn → Sn. The mutual position of the tectonic-magmatic structures of different ranks within the plume head obeys hierarchical and fractal laws.

The paper is focused on the regularities and character of the response of the regional landscapes of the Angara–Lena Plateau to variations in the global climate system during the Holocene. They were revealed by integrated studies of four peat bogs of the plateau — an important area for the understanding of the environmental dynamics in the entire Baikal region. Age models for the records obtained were provided by 16 radiocarbon dates. A spatiotemporal correlation of spore-pollen characteristics with the trend of δ¹⁸O records from global stratotypes was used to find out the possible causes of changes in the landscape conditions and climate of the Angara-Lena Plateau in the context of past changes in the global climate system. The plateau environment showed a dramatically varying response to global climate variations in the Middle–Late Holocene. Moreover, the observed intervals of reorganization in the regional environment took place in a quasi–millennial regime, in accordance with global climate rearrangement. However, not all the studied regions of the Angara–Lena Plateau made a synchronous or analogous response to global environment change. This emphasizes the complicated character of regional climate manifestations in the Holocene and necessitates the use of paleogeographical data from a wider range of territories.

We present results of research into the Holocene sediments of Lake Kiran, one of the small saline lakes with carbonate sedimentation in western Transbaikalia. The sediments were studied by X-ray diffraction (XRD), IR spectroscopy, analysis of stable ¹⁸O and ¹³C isotopes, laser granulometry, element analysis (SRXFA), etc. By the mathematical modeling of complex XRD patterns of lacustrine sediments, Mg-calcites with different Mg contents and excess-Ca dolomites have been determined in the assemblage of endogenic carbonate minerals. The obtained carbonate record gives an insight into the stratigraphic distribution of endogenic carbonates of the calcite-dolomite series, in which the number and proportion of phases with different Mg contents are determined by the Mg/Ca ratio, salinity, and total alkalinity of the lake water in the past. The abundance of excess-Ca dolomites in the sediments indicates that the lake is of shallow playa type. The mineral composition and crystallochemical structure of carbonates are in high correlation with the data of lithological analysis, results of determination of stable isotopes (δ¹⁸O and δ¹³C), and distribution of some geochemical indicators of sedimentation conditions. Several stages of the lake evolution depending on the regional climatic changes have been recognized. It has been established that the most arid environments in southern Buryatia were in the Subatlantic. Despite the highly arid climate in the region in the period under study (from 7 ka to the present), it underwent fluctuations toward humidification, in particular, at the Atlantic stage (the time of the lake formation) and in the recent decades, up to the present.