Vol 483, No 1 (2018)

The Olekma magmatic belt of the Selenga–Stanovoi Superterrane within the Central Asian mobile belt is traced for a distance of more than 700 km. As a result of U–Pb geochronological studies, it was established that granitoids of the Olekma Complex have the Paleozoic age (355 ± 2 and 358 ± 2 Ma) in the eastern and central part of the belt, whereas consolidation of granitoids with a similar composition in the western segment occurred in the Early Mesozoic (237 ± 1 Ma). The formation of Mesozoic granitoids of the Olekma Complex occurred under the conditions of lithospheric extension, whereas Late Paleozoic granitoids were most likely formed during the collision of the Selenga–Stanovoi Superterrane and structures of the Baikal mountain area.

U–Pb geochronological studies of detrital zircons from the Late Precambrian coarse sequence of the Ulutau massif are studied. The concordant ages of detrital zircons from the Satan Fm. composing the lower part of the Ulutau Series are formed by Neoproterozoic (740–888 Ma) and Paleoproterozoic (1989–2600 Ma) populations with the main peaks at 810 and 840 Ma, while less expressed peaks at 2017, 2036, and 2073 Ma. The concordant ages of detrital zircons from the upper part of the studied series, represented by coarse terrigenous rocks of glacial genesis (Baikonur Fm.), are predominantly within the intervals of 650–708, 721–729, and 754–889 Ma with peaks at 674, 721, 763, 772, 791, 821, and 840 Ma. The data obtained indicate that the lower age limit of coarse rocks from the Ulutau Series is about 670 Ma; these rocks formed mainly due to erosion of Neoproterozoic igneous complexes of the basement, which are widespread in the adjacent Maityube zone, with an insignificant role played by older basement rocks of the Ulutau massif.

The results of the first paleomagnetic study of a late Neoproterozoic magmatic complex on the Siberian paleocontinent (Siberia) using U–Pb geochronological data are presented. The igneous rocks of the Zimoveyniy massif (block) of the South Yenisei Ridge formed in an active continental margin setting and recorded the initial thermoremanent magnetization. Our calculations let us determine with reasonable certitude that in the late Ediacaran Siberia was located in the subequatorial latitudes.

This paper presents a new model of the distinct formation of groundwater of the aquifer system of the Northern Near-Caspian Region. The absence of sedimentary water displacement in plane is shown. An increase in mineralization and a wide range of characteristics of the composition and properties of rocks and waters are explained by processes of the mass-exchange in the water-rock system under conditions of low groundwater flow. The complex of the factors and conditions responsible for the integrity or displacement of sedimentary waters is determined, and it is suggested that it should be used to study the current and ancient sedimentary basins.

This article describes the peculiarities of hydrocarbon generation at great depths in the Earth’s crust. It is shown that all the conditions necessary for generation of oil and gas are kept at great depths in the crust in the zones of high pressures and temperatures. However, generation of hydrocarbons in such settings significantly differs from the processes of oil and gas formation at shallow depths. A complex system of mutual thermobaric factors and distribution of the oil and gas potential at great depths was revealed: the start of generation and the phase distribution of hydrocarbons in the section are largely affected by settling of abnormally high pore pressure, as well as by paleotemperatures that could differ considerably from the present-day ones depending on the age of deposits. It is shown that different thicknesses of catagenetic zones are related to the kinetic rate of oil and gas generation, which depends on the type of kerogen, the gradient of temperature change, pressure, lithology, and hydrogeological conditions of the host rocks, the sedimentation rate, and other factors.

U/Pb-isotope dating of detrital zircons from conglomerates of the reference section of the Demerdzhi Formation on the western slope of Mount Southern Demerdzhi was carried out. A cluster of the five youngest, reliably dated zircons with an average age of 154.1 ± 0.73 Ma was revealed, which indicates that the formation of conglomerates overlying the studied layer began to form not earlier than in the Late Kimmeridgian. The dating obtained forces us to reconsider the age of the Demerdzhi Formation, which was previously specified as Oxfordian–Early Kimmeridgian. New data on the age of thecoarse-grained sedimentary rocks of the Crimean Mountains advance concepts about Late Jurassic Cimmerian tectonic activity on the northern Tethys margin.

Experimental studies were performed in the Fe₃C–SiO₂–(Mg,Ca)CO₃ system (6.3 GPа, 1100–1500°C, 20–40 h). It is established that the carbide–oxide–carbonate interaction leads to the formation of ferrosilite, fayalite, graphite, and cohenite (1100 and 1200°С), as well as a Fe–C melt (1300°С). It is determined that the main processes in the system are decarbonation, redox-reactions of cohenite and a CO₂-fluid, extraction of carbon from carbide, and crystallization of metastable graphite (± diamond growth), as well as the formation of ferriferous silicates. The interaction studied can be considered as a simplified model of the processes that occur during the subduction of oxidized crustal material to reduced mantle rocks.

This study presents new chemical and isotope data for Ru–Os sulfides and coexisting platinum-group minerals (PGMs) within primary assemblage derived from the Verkh-Neivinsky dunite-harzburgite massif. PGMs were studied using electron microprobe analysis, laser ablation and multiple collector-inductively coupled plasma-mass spectrometry. The obtained results are consistent with: (i) high-temperature formation of Ru–Os sulfides and coexisting Os-bearing alloys, (ii) presence of two contrasting sources in the ore formation (i.e., subchondritic and suprachondritic), (iii) resemblance of the initial Os-isotope composition in coexisting laurite and Os-bearing alloy, (iv) significant Os-isotope variations in individual PGMs from the primary assemblage, and (v) potential of using model ¹⁸⁷Os/¹⁸⁸Os ages of PGMs for geodynamic paleoreconstructions.

This paper presents the results of U–Pb isotope–geochronological study on zircons from subalkali gabbros and granodiorites of the Dogaldyn intrusive massif located in the Karalon–Mamakan zone of the Baikal–Muya belt. The ages of 254 ± 2 and 256 ± 1 Ma yielded for rocks of the two main intrusion phases do not differ significantly from each other and correspond to the Late Permian period. The Nd-isotope and geochemical data indicate the relationship between the primary melts of intraplate rocks from the Dogaldyn Massif and various sources, including plume–mantle and ancient crustal ones. The manifestations of Late Permian intraplate magmatic activity in the Baikal–Muya belt could have been induced by the Iberian superplume framed by the Siberian trap province.

This paper considers the geochemical evolution of igneous and metasomatic rocks in the Baga-Gazryn Massif on the basis of new precision analytical data. The Baga-Gazryn rocks are characterized by enrichment in F, which is concentrated in Li–F mica, topaz, and fluorite. Along with F, zwitters and microclinites are enriched in Li, Rb, Cs, and ore elements Sn, W, Zn. High-charge elements (Zr, Hf, Nb, Ta, and Ti) and also Th and U are not very different in the Baga-Gazryn granites of various phases and metasomatic rocks.

The bulk composition of the silicate Moon (crust + mantle, BSM) is determined on the basis of inversion of gravitational and seismic data. It is shown that the mantle refractory oxides form two different groups depending on the thermal state. By the bulk Al₂O₃ content of ~3.0–4.6 wt %, the cold BSM models span the range of Al₂O₃ content of the silicate Earth (Bulk Silicate Earth, BSE), whereas the hot BSM models are significantly enriched in the Al₂O₃ content of ~5.1–7.3 wt % (Al₂O₃ content of ~1.2–1.7 × BSE) relative to BSE. In contrast, apart from the distribution of temperature, both BSM models are characterized by almost constant values of bulk FeO contents (~12.2–13.2 wt %) and MG# values (80.0–81.5), which are strongly distinct from those for BSE (~8 wt % FeO and 89 MG#). The results show that, for the geophysically possible distribution of temperatures, the silicate fraction of the Moon is enriched in FeO and depleted in MgO relative to BSE.

On the basis of combined analysis of data on a geological survey on a scale of 1 : 200 000 (1959–1960) and exploration works (1980–1990), it was found that the zones of higher radioactivity and related rich La–Ce ores are localized along linear faults 10–15 km long parallel to the axis of the Udzha Anticline. The HREE mineralization of the Y–Yb group is concentrated in sandstones and gravelstones of the Vendian Tomtor Formation, which unconformably overlap the Udzha Anticline on its wings. This indicates that the volatile flow has a deep (transmagmatic) origin rather than separation from magma. A carbonatite body with sulfide veinlets and dissemination is described with respect to a zone of high contents of La–Ce ores. The complex character of the Tomtor ores is explained by the juxtaposition of mineralization phases of various ages and composition: Nb and Sc–Th mineralization paragenetically related to the central ring structure of the intrusion and to the external rischorrite zone, respectively.

Parametric phenomena (amplification of vibrations and the appearance of combinational frequencies) emerging in rocks during seismoelectric transformations are studied experimentally under field conditions. The geological medium in which periodic seismic vibrations are excited attains the properties of the parametric electrical oscillation system. Under certain conditions, there is a possibility of emergence of parametric resonance owing to transformation of elastic energy to energy of alternating electrical field produced in the solid earth. It was also proven experimentally that the electrical response to elastic vibrations can appear not only as a result of seismoelectric effects of the second type, but also due to the existence of parametric seismoelectric effects of the first type.

The glacial and slope morphosculpture and correlated deposits of the Late Pleistocene and Holocene in the northeastern part of the Kilgan Mountains (Okhotsk–Kolyma region) were studied. The general three-element structure of loose cover in the glacial valley of Engteri Creek was established: moraine occurs in the lower part; proluvial deposits, in the middle; and covering deluvial deposits, on top. The sequence of postglacial evolution of slope processes was revealed. In the Atlantic (7245–5895 years ago), proluvial flows were the most active: they reached far beyond the slopes and covered moraine. Later, in the Subboreal, surface erosion intensified. The sedimentation rates in Dzhul’etta Lake were calculated. The glacial peak revealed in bottom sediments falls into the period of 19 410–13 880 years ago, with the smallest sedimentation rate, 6.3 cm/1000 years, which is lower compared to the underlying and overlying layers by a factor of two to three.