Home – Home – Jornals – Advanced Search

Based on geological data and the geochemical and isotopic (Sr, Nd) parameters of the Devonian volcanic associations of the Minusa basin, the main regularities of volcanism development are considered, the composition of magmatic sources is studied, and the geodynamic mechanisms of their involvement in rifting are reconstructed. The early stage of formation of the Minusa basin was characterized by intense volcanism, which resulted in differentiated and, more seldom, bimodal volcanic complexes composed of pyroclastic rocks and dolerite sills. At the late stage, only terrigenous deposits accumulated in the basin. It has been established that the basites are similar in composition and are intermediate in geochemical characteristics between intraplate rocks (OIB) and continent-marginal ones (IAB). The basites, like OIB, have high contents of all lithophile elements, which is typical of enriched mantle sources, and, like IAB, show negative anomalies of Nb, Ta, Ti, and, to a smaller extent, Rb, Th, Zr, and Hf, selective enrichment in Pb and Ba (and, sometimes, Sr), and a weak REE differentiation (7 < (La/Yb) N < 17). In contrast to the basins in other segments of the Devonian Altai–Sayan rift area, the igneous-rock associations in the Minusa basin are characterized by a worse expressed geochemical inhomogeneity of rocks and lack of high-Ti (>2 wt.% TiO2) basites. The Sr and Nd isotope compositions of the Minusa basites deviate from the mantle rock series toward the compositions with high radiogenic-strontium and low REE contents. This points to the melting of a mantle substratum (PREMA-type) and carbonate-rich sedimentary rocks, which were probably assimilated by basaltic magma. The correlations between the contents of trace incompatible elements in rocks with SiO2 = 53–77 wt.% testify to the assimilation of crustal substrata by parental basaltic melts and the subsequent differentiation of contaminated magmas (AFC model). We propose a model for the formation of primary melts with the simultaneous participation of magmatic sources of two types: plume and fluid-saturated suprasubductional, localized beneath the active continental margin.

The chemical composition of bottom sediments in the Chukchi and, partly, East Siberian Seas was studied. In the south and west of the Chukchi Sea, a zone has been detected with the accumulation of sediments rich in organic carbon, an increased background content and anomalies of sulfophile metals (Mo, Zn, Hg, Ag, Au), iron group metals (V, Ni, Co), and some PGE (Ru, Pt). This zone is confined to the neotectonic active system of rift troughs extending fr om Bering Strait and the eastern Chukchi Peninsula to the continental slope, wh ere it is bounded by the Cenozoic Charlie rift basin of the Canadian hollow. The geochemical features of the carbon-enriched sediments evidence that they formed under oxygen-deficient conditions and, sometimes, in suboxic and anoxic environments near endogenic water and gas sources. The high carbon and metal contents suggest that the fine-grained sediments in the rift troughs of the Chukchi Sea are a possible analog of some types of ancient highly carbonaceous sediments belonging to black shales.

In geologic objects of different characters and scales, the fractal properties of topography are related to the intensity of endogenic energy flows and the composition of geologic complexes. A good correlation between the topographic differentiation of the Khibiny pluton and the variables of different levels of its structural and compositional organization (mineral and chemical compositions of the rocks and minerals, rock texture, etc.) suggests that topography formation is an element of the self-organization of the Khibiny pluton. Analysis of the fractal dimensionality of topography in the Khibiny pluton, Primorye, and detailed areas in Transbaikalia revealed a coincidence of its maxima with the position of ore clusters, fields, and deposits, i.e., areas with the contents of elements significantly higher than their clarkes. All the above data suggest that the fractal properties of topography can be used as a prospecting criterion.

The Middle Oxfordian to lowermost Upper Kimmeridgian ammonite faunas from northern Central Siberia (Nordvik, Chernokhrebentnaya, and Levaya Boyarka sections) are discussed, giving the basis for distinguishing the ammonite zones based on cardioceratid ammonites of the genus Amoeboceras (Boreal zonation), and, within the Kimmeridgian Stage, for distinguishing zones based on the aulacostephanid ammonites (Subboreal zonation). The succession of Boreal ammonites is essentially the same as in other areas of the Arctic and NW Europe, but the Subboreal ammonites differ somewhat from those known from NW Europe and Greenland. The Siberian aulacostephanid zones – the Involuta Zone and the Evoluta Zone — are correlated with the Baylei Zone (without its lowermost portion) and the Cymodoce Zone/lowermost part of the Mutabilis Zone (the Askepta Subzone) from NW Europe. The uniform character of the Boreal ammonite faunas in the Arctic makes possible a discussion on their phylogeny during the Late Oxfordian and Kimmeridgian: The succession of particular groups of Amoeboceras species referred to successive subgenera is revealed by the occurrence of well-differentiated assemblages of typical normal-sized macro- and microconchs, intermittently marked by the occurrence of assemblages of paedomorphic “small-sized microconchs” appearing at some levels preceding marked evolutionary modifications. Some comments on the paleontology of separate groups of ammonites are also given. These include a discussion on the occurrence of Middle Oxfordian ammonites of the genus Cardioceras in the Nordvik section in relation to the critical review of our previous paper. The discussion shows that the oldest deposits in the section belong to the Middle Oxfordian, which results in the necessity for some changes in the foraminiferal zonal scheme of Nikitenko et al. The ammonites of the Pictonia involuta group are distinguished as the new subgenus Mesezhnikovia Wierzbowski and Rogov.

Results of the investigation of reasons causing the destruction of molybdenum containers used for sintering the pellets of fuel uranium dioxide are reported. An effect of niobium ion implantation changing the microstructure and mechanical properties of molybdenum was investigated. It was demonstrated that niobium prevents the formation of carbide, nitride and oxide phases on the boundaries of molybdenum grains, causes the rate of metal grain growth in the course of recrystallization to decrease and stabilizes mechanical properties thus increasing the operational reliability by 30–60 %.

UDC 669.28:54

A new efficient broad spectrum agent comparable in efficiency with chemical fungicides was developed on the basis of the aqueous solution of the salts of fir extract with bisamine, with the addition of the salt of 2,4-dichlorophenoxyacetic acid with bisamine and the Usnea lichen extract. The agent suppresses the development of fungal diseases and increases the yield of spring wheat and potato.

UDC 547.99+632.934.1

A method is proposed for the sulfation of microcrystalline cellulose in the system N,N-dimethylformamide/chlorosulphonic acid with preliminary treatment of cellulose with ultrasound in an organic solvent. It is demonstrated that the treatment with ultrasound results in an increase in the reactivity of cellulose in the sulfation reaction as well as in occurring the sulfation in homogeneous medium. The action of ultrasound on microcrystalline cellulose is accompanied by a decrease in the polymerization level of the cellulose material and does not affect its crystallinity index. Water-soluble cellulose sulphates with the substitution level up to 1.5 were obtained using the method proposed.

UDC 541.64

The surface of oxides Mn₃O₄, Mn₂O₃ and MnO₂ subjected to mechanical activation with the help of high-intensity grinding was studied by means of X-ray photoelectron spectroscopy. It was discovered that the surface layers of all the three oxides were transformed during mechanical activation into Mn₂O₃ possessing increased chemical stability against environmental action. The results are due to the thermal effect and the catalytic action of extrinsic iron in the surface layer of Mn_mO_n particles.

UDC 546.713'712–31'713–31'714–31:544.3.032.2:543.428.4

The possibility of single-stage synthesis of isoprene from 1,3,5-trioxane and trimethylcarbinol in the presence of heterogeneous catalyst – strongly acidic macroporous cation-exchange resin – was established. The composition of the reaction mixture was determined by means of gas-liquid chromatography. Along with isoprene, unreacted trimethylcarbinol was detected, as well as by-products: unsaturated isoamylenic alcohols and 4,4-dimethyldioxane-1,3 – precursors of isoprene; the formation of an additional amount of isoprene during the decomposition of these compounds is possible. Optimal process conditions were chosen, providing the degree of trioxane conversion up to 99 %, selectivity of the process with respect to isoprene 65 %, and the yield of isoprene per transformed trioxane 64 %. In comparison with the existing two-stage methods of isoprene synthesis from the aqueous solution of formaldehyde and isobutylene, the proposed method allows one to decrease energy consumption and diminish the amount of waste water due to the “soft” technological conditions of the process.

UDC 54.05:542:547.315.2:504.064.043:620.9

Sorption of platinum chloro complexes from solutions with the help of oxidized carbon sorbents was studied. An effect of the oxygenated surface functional groups of oxidized carbon sorbents on their sorption capacity was studied using IR spectroscopy, pH-metry, titrimetry. Sorption isotherms for H₂PtCl₆ and Н₂PtCl₄ were obtained. It was established that the capacity of the sorbent with respect to H₂PtCl₆ increased by a factor of 2.4.

UDC 544.723: 546.26: 546.92