Vol 476, No 1 (2017)

U–Pb SHRIMP dating of zircons from metamorphic rocks of the crystalline basement of the Omolon-Taigonos area (northeastern margins of Asia) has been used to determine the periods of early endogenic activity of the crust. These periods correlate to the time of formation of the magmatic rock protolith (3.2–3.3 Ga), the stage of regional metamorphism (2.6–2.8 Ga), and the superimposed granitization. The resulting data can be used to reconstruct the history of development of the crust in the Precambrian.

Spinel peridotite, metamorphosed in high-pressure conditions, was first described within the Western part of the Central Asian Orogenic Belt. The spinel peridotite has the characteristics of Mg–Cr ultramafites indicating the mantle origin of its protolith. The preliminary estimation of the metamorphism peak for the model system MgO–Al₂O₃—SiO₂–Cr₂O₃ (MASCr) is 10–19 kbar at 680–800°C.

We have studied Pb isotopic systems of K-feldspar, pyrite, and pyrrhotine from gabbroids and ore of the Velimyaki Early Proterozoic massif in the northern Ladoga region in the southeastern part of the Fennoscandian Shield. The isochronous Pb–Pb age of sulfides has been determined as ∼450 Ma, which corresponds to intersection of the regression line with the lead accumulation curve with μ = 10.4–10.8; the model Pb age of sulfides is close to isochronous under the condition that the composition of lead evolved from a geochemical reservoir with an age of 1.9 Ga. The isotopic parameters of the lead in sulfides and K-feldspar indicate their formation in upper crust conditions (μ = ²³⁸U/²⁰⁴Pb > 10). From the obtained data, it follows that the isotopic composition of lead in K-feldspar corresponds to a Proterozoic age (1890 Ma) of magmatic crystallization of the rocks in the massif, and strongly radiogenic lead sulfides testify, with the greatest probability, to the later (Caledonian) formation of sulfide ores.

This communication considers the ideas about the geological structure of the southwestern Mendeleev Rise belonging to the East Arctic rises of the Arctic Ocean. These ideas have resulted from analyzing the data obtained from bathymetric surveys, visual observations, and bottom coring using the technical tools of a research submarine. We distinguished the lower sequence of quartzite sandstones and dolomites, which has a visible thickness of about 230 m and occurs in the lowermost visible section, at depths between 1500 and 1270 m. This sequence is superimposed with stratigraphic and angular unconformity by the upper sequence of limestones and sandstones having a visible thickness of 40 m. The lower sequence is pierced by subvolcanic rocks of basaltic to andesitic composition, and in the lowermost part of the slope, a tuffaceous sequence having a visible thickness of 50 m adjoins it.

Two new sulfide fields (Yubileinoe, 20°09′ N, and Surprise, 20°45.4′ N) were discovered between 20°01′ and 20°54′ N within the Russian Application Area of the Mid-Atlantic Ridge (MAR). The Yubileinoe field is located at a depth of 2300–2550 m in the near-top area of the first rift ridge, which is a boundary of the western wall of the rift valley. This new field and the Zenith-Victory field, which was previously discovered in the eastern wall, occur symmetrically relative to the rift valley of this MAR segment. The Surprise field at a depth of 2800–2850 m is situated in the eastern wall of the rift valley, on the slope of the volcanic uplift. After the discovery of these inactive sulfide fields, the number of hydrothermal fields within the Russian Application Area reached ten.

The metamorphic complexes in the northern part of the Olkhon terrane (Zunduk megazone), Central Asian Fold Belt, are studied. It is found that the age of gneiss–granites, which correspond to granites of type I formed within the active continental margin, is 800 ± 11 Ma, whereas the age of the protolith of epidote–muscovite–feldspar–quartz schist, which formed by metamorphic reworking of island-arc volcanic rocks, is 650–630 Ma. New results and those published earlier show that the structure of the Olkhon terrane contains traces of at least three stages of different ages when suprasubduction processes were manifested. The earliest episode (∼850‒800 Ma) occurred within the Panthalassa, and the subsequent ones (∼650‒620 and ∼500 Ma) occurred in the Paleoasian Ocean. New data give us grounds to consider protoliths of the studied rocks from the northern flank of the Olkhon metamorphic terrane as products of convergence-related processes that took place within the limits of the paleooceans in the Late Precambrian, rather than in the Pleoproterozoic as was supposed earlier.

For the first time in Russia, a Hadean zircon grain with an age of 3.94 Ga (ID-TIMS) has been discovered in high-aluminous garnet granulites of the Aldan Shield among the U–Pb zircons with an age from 1.92 Ga. In this connection, the problems of its parental source, the petrogenesis of granulites that captured this zircon, and the mechanism of occurrence of these deep rocks in the upper horizons of the crust have been solved. The comparison of the geochemistry of garnet granulites and the middle crust has shown that the granulites are enriched in the entire range of rare-earth elements (except for the Eu minimum), as well as in Al₂O₃, U, and Th and are depleted in the most mobile elements (Na, Ca, Sr). In the upper part of the allitic weathering zone of the middle crust, which formed under conditions of arid climate, this zircon grain was originated from the weathered granites from the middle crust. In the latter case, they were empleced discretely in the upper granite–gneiss crust under high pressure conditions (the rutile age is 1.83–1.82 Ga). The zircon with an age of 3.94 Ga is comparable to the Hadean zircons from orthogneisses of the Acasta region (Canadian Shield, 4.03–3.94 Ga).

U–Pb LA ICP–MS dating of zircon from rocks of the Nekrasov gabbro–granitoid complex within the eastern margin of the Middle Urals was performed. The average U–Pb age calculated from three concordant measurements (326 ± 8 Ma) shows that their intrusion occurred at the Serpukhov Stage of the Early Carboniferous. According to the ideas on periodization of magmatic processes within the eastern sector of the Middle Urals, the formation of this complex corresponds to the final episodes of the continental marginal (supersubduction) magmatism.

The results of X-ray structural, electron-microscopic, and X-ray spectral microprobe studies of Al-based metal solid solutions that underwent nuclear disintegration and that were discovered in nature for the first time are presented. Based on the similarity to technical counterparts, it is suggested to recognize the previously unknown alloys as natural duralumin.

Based on analysis of new data on the geodynamical nature, ages of formation, and magmatic sources of contrasting rocks from the tectonic mélange of the Yenisei shear zone, the chronological sequence related to early stages in the evolution of the Paleoasian Ocean was established. The data obtained specify the legend and stratigraphic scheme of the Yenisei Group and peculiarities in the evolution of the Sayany–Yenisei accretionary belt at the final stage of its Neoproterozoic history.

This report considers features of the geochemical composition of obsidian from beach sediments of Krasnoe Lake along the lower course of the Anadyr River, as well as from lava–pyroclastic rocks constituting the lake coastal outcrops and the surrounding branches of Rarytkin Ridge. The two geochemical types of obsidian, for the first time distinguished and researched, correspond in their chemical composition to lavas and ignimbrite-like tuffs of rhyolites from the Rarytkin area. The distinguished types represent the final stage of acidic volcanism in the West Kamchatkan–Koryak volcanic belt. It was assumed that the accumulation of obsidian in coastal pebble beds was caused by the erosion of extrusive domes and pyroclastic flows. The geochemical studies of obsidian artifacts from archeological sites of the regions of the Sea of Okhotsk, the Kolyma River, and the Chukchi Peninsula along with the correlation of geological and archeological samples show that Krasnoe Lake was an important source of “archeological” obsidian in Northeastern Siberia.

A new method of analytic continuation of gravitational and magnetic fields, which is based on the theory of continued fractions, is proposed. The method allows calculation of the geophysical fields of various origins by their measurements on the surface at depths above and below the sources of anomalies, as well as direct determination of the depth and forms of these sources without a priori information. The calculation results are given in examples of theoretical models, which prove the efficiency of the method.

The paper describes the indispensable functional relationship between large-scale hydrocarbon trap saturation and limited space overflow-injection hydrogeological processes outside the regional action of elision and artesian mechanisms. We propose a set of qualitative criteria and quantitative indicators of oil and gas potential, making it possible to minimize the risks of geological exploration and production and create individual forecast zones and priority areas of oil and gas accumulation.

The role played by the Earth’s rotation is very important in problems of physics of the atmosphere and ocean. The importance of inertia forces is traditionally estimated by the value of the Rossby number: if this parameter is small, the Coriolis force considerably affects the character of movements. In the case of convection in the Earth’s mantle and movements of lithospheric plates, the Rossby number is quite small; therefore, the effect of the Coriolis force is reflected in the character of movements of the lithospheric plates. Analysis of statistical data on subduction zones verifies this suggestion.

It was established that along with permafrost degradation, the processes of permafrost aggradation occur in the modern low accumulative surfaces of Kara Sea. The cycle of observation over the permafrost thermal regime was performed. The mean annual temperatire of the permafrost varies from – 3.5 to – 4.8°C; the thermal flux into the permafrost can reach 8 W/m². The methane genesis process is realized only in the seasonally thawed layer. It was found that temperature – 4.0°C is threshold for the bacterial methane production.

It was shown that an improved quasi-rhythm method can make it possible to predict the annual side inflows into the hydrological sections of the Volga-Kama Hydropower Plants (HPP) Cascade with a one-year lead time with high quality and good forecast verification.

Using an archival database from the Institute of Natural and Technical Systems, the low-frequency variability of oxygen dissolved in the deep-water and northwestern parts of the Black Sea for the period of 1955–2004 is analyzed. The upper mixed layer (UML) is characterized by quasi-periodic variability in the dissolved oxygen concentration in the interdecadal scale. Deeper, a long-term decrease in the oxygen concentration is recorded.