Home – Home – Jornals – Advanced Search

Analysis and summary of publications on southern East Sayan, eastern Tuva, and northern Mongolia have shown that the late Pleistocene glaciation covered a large area and had a complicated dynamics of glacier advance and retreat. Starting with MIS 5, the Todza Basin and, partly, the Oka Plateau, Azas Volcanic Plateau, Mondy Basin, and river valleys in southern East Sayan were periodically covered with ice. The thickness of ice in the eastern Todza basin was 700 m, on the Azas Volcanic Plateau it reached 300–600 m, and in the val-leys of southern East Sayan it is estimated as 700–800 m. The thickness of ice in the Mondy Basin was 300–350 m. Geological and geomorphological studies and isotope surface exposure dating (10Be method) of boul-ders from terminal moraine complexes have provided evidence for extensive MIS 2 glacier advance in the Mondy Basin and in the Sentsa, Jombolok, and Sailag river valleys (southern East Sayan). The average age of exposure for three groups of samples is 14, 16, and 22 ka.

Isolated lenses of diamictites laying discordantly over the Late Riphean (Cryogenian) Kirgitei Forma-tion were found in the immediate vicinity of the Vendian Taseeva Group stratotype in the Taseeva River val-ley and assigned to the Shishina Member a few meters in visible thickness. The Shishina diamictites are, likely, of glacial origin as they (i) lie at the base of the Vendian section, (ii) consist of unsorted dolomitic clasts from fine gravel to more than 0.5 m boulders suspended in a mud matrix, and (iii) show glacial striation on clasts. The glacial origin is further supported by the morphology of stones, which resemble a smoothing iron or a bullet, with a swelly top, a flat bottom, and a steeply cut rear and form clusters produced by disinte-gration of larger boulders. The stones bear signatures of cleavage, cracks, grooves, and striation on the faces, while the matrix looks undeformed. The Shishina Member has no genetic relation with the underlying Kirgitei Formation but rather correlates sedimentologically with the Ulyakha Member tillites at the base of the Ven-dian Marnya Formation (Oselok Group) in the Sayan foothills. The Shishina Member stones may derive from the Late Riphean (Cryogenian) Dzhura Formation exposed 4 km downstream of the site along the Taseeva. They occur near the base of the Aleshinsky Formation (lowermost unit of the Taseeva Group) of cross-bedded glaciofluvial sandstone, gravelstone, conglomerate, and sandy gravel mixtite transported from east to west (from the Siberian Craton interior to its margins) and deposited in channel bars or as gravel lags. The lower member of the Aleshinsky Formation comprises two associations of clasts: (i) coarse quartzose sand and gravel and (ii) fine and medium quartz and lithoclastic sand. Rocks in the former are well rounded, with traces of wind erosion, while the latter association is composed of mechanically eroded angular material transported to short distances from a metamorphic and metasedimentary source on the Craton margin. The Aleshinsky clastics have their composition and grain size patterns similar to those of the glaciofluvial Plity, Nersya, and Kedrovy members of the Marnya Formation in the Sayan area. According to sedimentological evidence, the Shishina diamictites are tillites identical to the Ulyakha moraine at the base of the Sayan Oselok Group and may be a missing link in the Taseeva Group stratigraphy.

The composition of stable carbon and oxygen isotopes in the section of an isolated carbonate platform is analyzed. Traces of several global and subglobal transgressions and regressions have been found in the limestone strata. Some of these phenomena were associated with the Upper Kellwasser (at the Frasnian–Famennian boundary) and multiphase Hangenberg (at the Devonian–Carboniferous boundary) Events. Never-theless, there were no considerable sea level fluctuations in the platform water area. There is no evidence for subaerial erosion. The bottom water during sedimentation was mostly in oxic conditions.

We present results of study of mineral assemblages and PT-conditions of metamorphism of mafic gar-net–two-pyroxene and two-pyroxene granulites in the Early Precambrian metamorphic complex of the An-gara–Kan terrane as well as the U–Pb age and trace-element and Lu–Hf isotope compositions of zircon from these rocks and the zircon/garnet REE distribution coefficients. The temperatures of metamorphism of two-pyroxene granulites are estimated as 800–870 to ~900 ºC. Mafic garnet–two-pyroxene granulites contain gar-net coronas formed at 750–860 ºC and 8–9.5 kbar. The formation of the garnet coronas proceeded probably at the retrograde stage during cooling and was controlled by the rock composition. The age (1.92–1.94 Ga) of zircon cores, which retain the REE pattern typical of magmatic zircon, can be taken as the minimum age of protolith for the mafic granulites. The metamorphic zircon generation in the mafic granulites is represented by multifaceted or soccerball crystals and rims depleted in Y, MREE, and HREE compared to the cores. The age of metamorphic zircon in the garnet–two-pyroxene (~1.77 Ga) and two-pyroxene granulites (~1.85 and 1.78 Ga) indicates two episodes of high-temperature metamorphism. The presence of one generation (1.77 Ga) of metamorphic zircon in the garnet–two-pyroxene granulites and, on the contrary, the predominance of 1.85 Ga zircon in the two-pyroxene granulites with single garnet grains suggest that the formation of the garnet coro-nas proceeded at the second stage of metamorphism. The agreement between the zircon/garnet HREE distribu-tion coefficients and the experimentally determined values at 800 ºC suggests the simultaneous formation of ~1.77 Ga metamorphic zircon and garnet. Zircon formation by dissolution/reprecipitation or recrystallization in a closed system without exchange with the rock matrix is confirmed by the close ranges of 176Hf/177Hf val-ues for the core and rims. The positive εHf values (up to +6.2) for the zircon cores suggest that the protoliths of mafic granulites were derived from depleted-mantle source. The first stage of metamorphism of the mafic granulites and paragneisses of the Kan complex (1.85–1.89 Ga) ended with the formation of collisional grani-toids (1.84 Ga). The second stage (~1.77 Ga) corresponds to the intrusion of the second phase of subalkalic leucogranites of the Taraka pluton and charnockites (1.73–1.75 Ga).

Omphacite is a typomorphic mineral of eclogites, which is inappropriate to mineral assemblages of per-idotites. Nevertheless, findings of this mineral in inclusions in peridotitic diamonds can be considered as indi-rect evidence for the existence of this paradoxical mineral assemblage. In this paper we present experimental results on the interaction between carbonate-bearing amphibolite and olivine that model processes operated at the crust–mantle boundary in subduction zones. The experiments demonstrate growth of omphacite at the in-terface between acid melt and peridotite media at 2.9 GPa and 850–900 ºC; the omphacite coexists either with garnet and orthopyroxene or with phlogopite. The synthetic omphacite is exclusively of reactive-magmatic origin and does not form in metasomatic way. Findings of omphacite inclusions in peridotitic diamonds and in some pyroxenites from kimberlites are discussed in scope of the obtained experimental data.

Upper-mantle xenoliths in Cenozoic basalts of northwestern Spitsbergen are rocks of peridotite (spinel lherzolites) and pyroxenite (amphibole-containing garnet and garnet-free clinopyroxenites, garnet clinopyroxenites, and garnet and garnet-free websterites) series. The upper mantle section in the depth range 50-100 km is composed of spinel peridotites; at depths of 80-100 km pyroxenites (probably, dikes or sills) appear. The equilibrium conditions of parageneses are as follows: in the peridotites - 730-1180 ºC, 13-27 kbar, and oxygen fugacity of -1.5 to +0.3 log.un.; in the pyroxenites - 1100-1310 ºC, 22-33 kbar. The pyroxenite minerals have been found to contain exsolved structures, such as orthopyroxene lamellae in clinopyroxene and, vice versa, clinopyroxene lamella in orthopyroxene. The formation temperatures of unexsolved phases in orthopyroxene and clinopyroxene are nearly 100-150 ºC higher than the temperatures of the lamellae-matrix equilibrium and the parageneses in the rock. The normal distribution of cations in the spinel structure and the equilibrium distribution of Fe2+ among the M1 and M2 sublattices in the orthopyroxenes point to the high rate of xenolith ascent from the rock crystallization zone to the surface. All studied Spitsbergen rock-forming minerals from mantle xenoliths contain volatiles in their structure: OH-, crystal hydrate water H2Ocryst, and molecules with characteristic CH and CO groups. The first two components are predominant, and the total content of water (OH- + H2Ocryst) increases in the series olivine → garnet → orthopyroxene → clinopyroxene. The presence of these volatiles in the nominally anhydrous minerals (NAM) crystallized at high temperatures and pressures in the peridotites and pyroxenites testifies to the high strength of the volatile-mineral bond. The possibility of preservation of volatiles is confirmed by the results of comprehensive thermal and mass-spectral analyses of olivines and clinopyroxene, whose structures retain these components up to 1300 ºC. The composition of hypothetic C-O-H fluid in equilibrium (in the presence of free carbon) with the underlying mantle rocks varies from aqueous (>80 % H2O) to aqueous-carbonic (~60 % H2O). The fluid becomes essentially aqueous when the oxygen activity in the system decreases. However, there is no strict dependence of the redox conditions on the depth of formation of xenoliths.

Results of observation of generation of aerosol particles and drops in mixtures of saturated water vapor with air and molecular gases are described in the paper. The kinetics of the aerosol and drop generation was studied in the absence and under impact of monokinetic beam of electrons on the gas mixture with supersaturated water vapor, formed in the process of the controllable pressure unloading of the prepared gas mixture from a spherical chamber of 1.4 m in diameter to vacuum reservoir of 40 m³ in volume. The kinetics of generation of aerosol particles and drops was recorded by the method of laser beam (drop) small-angle scattering and with the help of aerosol spectrometer (particle). Experimental results show significant dependence of generation of drops and particles on the impact of ionizing radiation. Three-dimensional computer simulation of the process of supersaturated water vapor condensation on ions by methods of Boltzmann lattice equations (LBE) and molecular dynamics (MD) describes qualitatively the obtained experimental results.

In April, 2011, at Northern Hemisphere midlatitudes, a long-term anomalous decrease of the total ozone content was recorded over a number of regions, attributed to echoes of large-scale Arctic ozone anomaly, observed in March. In this paper, we showed that stratospheric ozone destruction over Tomsk during that period was caused by eruption of Indonesian volcano Merapi in November 2010. NOAA HYSPLIT model was used to analyze the motion of air masses in the lower stratosphere on the way from coordinates of volcanic ejection from the moment of eruption until late April. It was found that air masses, containing volcanic aerosol, came to the Northern Hemisphere midlatitudes in late March 2011, in agreement with high aerosol content recorded in the stratosphere over Tomsk during that period. Based on analysis of temperature and ozone anomalies in the stratosphere over Tomsk, we showed that they manifested themselves by the volcanic soot present in aerosol composition.

In the current work, the result of an investigation of temperature effect of smoke aerosol in the summer season over the central part of Yakutia during the period 2004−2014 are presented. The data of ground-based and satellite measurements and also of climate models NCEP/NCAR and ERA-Interim, which are based on regular meteorological observations and aerological and satellite informations are used. It is first showed that a disturbance of atmosphere by aerosol particles which is caused by heat sources of forest area lead to a decrease of solar radiation flow, and, in the presence of a negative phase of upward longwave radiation, a surface air temperature drop is observed.

A set of photoacoustic spectrometers in order to study the weak aerosol and molecular absorption of laser pulses by atmospheric air in UV, Visible and near infrared spectral regions is designed. The common element of spectrometers is a photoacoustic detector with a temporal resolution of signals and a built-in acoustic hub consisting of two parabolic mirrors. The detector is characterized by a high sensitivity (minimum measured value of the absorption coefficient reaches ~ 10^–9 cm^–1 at a laser beam radius of 1.5 mm and a laser pulse energy of 50 mJ) and by lack of background signals associated with the absorption of radiation at the inner surface of the photoacoustic cell. Some results of measurements of non-selective molecular and aerosol absorption in gases and air, including non-linear absorption of high-power femtosecond laser pulses are presented.