Volume 480, Nº 2 (2018)

The results of LA–ICP–MS U–Pb analyses of detrital zircons from the Precambrian deposits of Luga–Ladoga monocline are discussed. The age spectra of the zircons separated from the Riphean to Upper Vendian sandstones from the Shotkusa-1 well demonstrate dominance of the Paleo- and Mesoproterozoic grains while the Archaean zircons are subordinate. The Riphean debris sources were local swells of the Northern Ladoga basement. The sequence interval presumably corresponding to the Vasilieostrov Formation (Upper Vendian) has yielded not only Paleo- and Mesoproterozoic zircon ages, but Neoproterozoic as well, implying a Timanide provenance: these zircons (527 ± 9 and 516 ± 13 Ma) allow deposition of a significant part of the Shotkusa-1 sequence at the very beginning of the Cambrian.

It is revealing a clear tendency of the fields layered in producing belt of oil-pays, extending in the limit of the sea depth from 400 m to 3000 m at the continental slope and possibly 4000 m at the continental rise.

The tectogenesis of the Atlantic Ocean segments is complicated by the axial difference in spreading half-velocities, which causes additional shear displacements between the lithospheric blocks along the transform faults. The intensity of these processes and density of the fault zones iis related to the presence of “cold” sublithospheric lenses along the MAR at a depth of 500 km.

The first data on study of individual fluid inclusions in the Zhilnoye deposit have been obtained. It has been found that the gold-bearing quartz veins of the deposit were formed by heterogeneous hydrothermal fluids with low salt concentrations (0.2–3.6 wt% equiv. NaCl under intermediate temperature conditions of 246–350°C). The fluid pressure was 80–160 bar corresponding to 0.3–0.6 km depths of formation under hydrostatic conditions. The parameters of the mineral-forming fluids of the Zhilnoye deposit correspond to typical parameters of the fluids of epithermal deposits.

The long-term data (1950–2017) on the chemical composition of the water from the source of the Angara River, which is the only run-off from Lake Baikal, a large and clean fresh water reservoir, are presented. The absence of water contamination despite the anthropogenic influence is shown. The similarity and constancy of the current composition of the waters in the lake and the Angara River are recorded. It is recommended to continue geochemical studies of this unique world heritage site.

Gallium-containing chlorite, mica, and magnetite (up to 14, 13, and 5–7 wt % of Ga) along with Ga hydroxides (oxyhydroxides?) were found for the first time in massive sulfide deposit in the Urals. The minerals identified within the cement of chalcopyrite–sphalerite breccias of the Shemur copper–zinc–massive sulfide deposit (Northern Urals) are associated with Ga-enriched sphalerite, chalcopyrite, and, less commonly, pyrite (33–364, 67–363, and 4–230 g/t, respectively).

The results of study of the Nd and Sr isotope compositions of the Nb ore minerals (pyrochlore and aeschynite groups) and rocks from the Ilmenogorsk–Vishnevogorsk and Buldym carbonatite complexes of the Ural Fold Belt are presented. It has been established that pyrochlores of the early stages of ore formation and the IVC miaskite-carbonatite rocks have a single substance source corresponding to a mantle moderately depleted source according to isotope parameters. The crustal components, along with mantle, participate in the processes of ore formation within the Buldym complex.

One unsolved problem of Archean metallogeny of the Russian part of the Fennoscandian Shield is related to the period of formation of orogenic gold deposits, the age of which was previously considered Early Proterozoic. Comprehensive studies identified the complex evolution of ores from the Novye Peski deposit and the first Neoarchean Sm–Nd isochron isotopic age (2583 ± 16 Ma) of the formation of orogenic gold of the Karelian Craton. A significant positive ε_Nd(t) value of +4.7 of gold-bearing metasomatites probably points to the link between the ore-forming fluid and the deep mantle source.

The results of studying an aggregate of graphite-and-diamond crystal in tourmaline 5 μm of the Kokchetav massif by the method of transmission electron microscopy are presented. The detail studies of the interface between the crystals of graphite and diamond have revealed the absence of disordered graphite that is detail partially graphitized diamond. Intense deformation changes in the graphite crystal occurred after it was captured by tourmaline at the regression stage, which led to considerable kinking of the graphite crystal along the a-axis. Thus, the coexistence of graphite and diamond crystals cannot be unambiguously interpreted as a product of partial diamond graphitization. Graphite could have crystallized syngenetic with a diamond crystal or at the retrograde stage in the graphite stability field.

The first results are presented for the synthesis of diamond at 6.5 GPa and 1600°C during migration of molten iron through a silicate matrix, which is composed of olivine crystals with interstitial graphite. The experiment shows that diamonds in the Earth’s mantle and the terrestrial planets could have formed during differentiation. Diamond crystals, which were formed during iron segregation of the Earth’s differentiation, could be centers for further crystallization of mantle diamonds.

We have analyzed the geodynamic evolution of the lithosphere and upper mantle of the Amerasian basin based on the stress-strain state simulation. It is shown that the asthenospheric spreading in the return upflow region of the mantle convection, results in formation of two local uplifts, which can be interpreted as Lomonosov Ridge and Mendeleev/Alfa Ridge. The further long-term action of the mantle convection leads to formation of Makarov and Podvodnikov Basins.

Based on complex analysis of the results of instrumental observations during strong atmospheric disturbances, it is shown that hurricanes and squalls are accompanied not only by high wind velocities, but also by high-amplitude microbaric variations, variations in amplitudes of the microseismic background, and the vertical component of the electric field. It is established that 1–4 hours before the onset, squalls and hurricanes are characterized by increased amplitudes of microbaric variations in the range of periods of 2–6 min, as well as by low-frequency variations in the electric field and variations in the microseismic background, which together with the meteorological parameters can be considered as a complex prognostic criterion of an impending hurricane (squall).

A fundamentally new conclusion that zones of high seismic activity are controlled by electroconducting (fluid-saturated) fragments rather than by the entire deep fault is drawn. It is shown that the areal abundance of earthquake foci in geoelectric blocks of the Earth’s crust within Sakhalin and Vietnam containing electroconducting formations is mostly controlled by their roof occurring at a depth of ≤15 km.

The isotope-oxygen composition of ice wedges, ground ice, ice of the intrusive-segregated seasonal mound, and segregated ice of Eastern Chukotka near Koolen Lake, the settlement of Lavrentiya on the Chul’kheveem River, the settlement of Lorino, and the city of Anadyr on the Onemen Bay coast was studied. The comparison of isotopic diagrams showed that the variations in δ¹⁸O of the Holocene ice wedges of Eastern Chukotka did not exceed 2‰, which indicates the insignificant variability of climatic winter conditions in the late Holocene. The long-term mean-January temperature values varied less than 3°C according to calculations from the equations of interrelation between air temperature and the isotopic composition of the wedges.

The aim of this work was to analyze the observation data on the dynamics of the species composition of ice flora and fauna in the polar region of the Arctic Ocean. The analysis was based on the materials obtained by the Pan-Arctic ice camp expedition in April 2007–2011 and 2015 [1]. We indicated the dynamics of the species composition of flora by diatoms living in the ice, and of fauna by amphipods and copepods with habitats allocated to the bottom ice surface. The dynamics of the species composition of biota is analyzed in this work without specification of its natural or anthropogenic factors.

For the first time, the reconstruction of variations in the duration over several hundred years was conducted on the basis of models developed by comparing hydrometeorological observations and detailed scanning of the chemical composition of bottom sediments accumulated during the corresponding period. The gauge models for the reconstruction of air temperature and ice cover of the water area for three sites in the northern part of the Chukchi Sea have been developed. During the reconstruction, an insignificant increase in the duration of the ice-free period during the Little Ice Age was established, which does not coincide with the changes in the temperature regime that took place. It is concluded that the dynamics of the inflow of warm Pacific waters through the Bering Strait had the predominant influence on the ice regime of the Chukchi Sea.

The results of studies in the paleochannel of the Volga River, which was discovered earlier on the northwestern slope of the Derbent Basin, Caspian Sea, are presented. Seismoacoustic profiling in the paleochannel, combined with placement of submerged buoy stations equipped with current gauges, water temperature gauges, and sediment traps showed that the channel is not silted and cold heavy water is transported along it to the deep sea part of the sea, avoiding the general water transit along the western coast of the Central Caspian Sea. The preliminary calculations show that water discharge through the channel to the near-bottom part of the sea can be about 8–10 km³/yr.