Том 484, № 1 (2019)

The variety of sizes and morphology of grains and chemical composition of native Au, and the diversity of mineral productive associations in the new ore occurrences of the Western and Central Taimyr (the Minina–Bolshevik miogeocline and the Shrenk–Faddeevskaya accretionary mineragenic zones) indicate the complex multicomponent composition of ore-forming systems and different physicochemical conditions of the formation of gold ore mineralization. The native Au characteristics and specific features of the geological structure of the objects point to the significant gold ore potential of the Central Sector of the Russian Arctic.

It is proposed that unstable temperature conditions in the Late Wuchiapingian and Early Changhsingian (Late Permian) changed in the Boreal Superrealm to less contrasting climatic conditions in the Late Changhsingian and Early Induan (the formation time of trap formation of the Siberian Platform), with a stable trend of increasing temperature in the Early Triassic. The problem of the absence of signs of mass extinction of marine organisms at the Permian–Triassic boundary in the Boreal Superrealm is discussed.

The results of U–Pb-isotopic dating of detrital zircons from sandstones of the Proterozoic Pogor’uy Formation, occurring to the north and south of the East Angara block of Yenisei Ridge, are presented. The sandstones of the northern part of the East Angara block are dominated by Archean and Paleoproterozoic populations of detrital zircons, while the samples from the southern part of the East Angara block have been revealed up to 25% of Mesoproterozoic age grains. The detrital zircon ages allow limiting the maximum sedimentary age of the Pogor’uy Fm. and the entire interval of its formation to 1.2–0.9 Ga. The paleogeographic features of the Pogor’uy Fm. deposition in the context of the existing opinions on the location of Siberia within the Rodinia supercontinent were examined.

This paper analyzes the rose diagrams of the directions of 439 faults of the Variscian province, 476 faults of the Caledonian province, and 603 presently active faults of Tien Shan. It is shown that more than half of the faults of the Caledonian province of Tien Shan are a result of Late Paleozoic orogenesis, which spanned its entire territory. Our data indicate that seismic events of Tien Shan have resulted in no formation of new disjunctive dislocation in many cases exhibiting displacements along Paleozoic faults. This information should be taken into account during selection of building areas.

Geochronological (LA–ICP–MS) U–Th–Pb studies of detrital zircon of the Late Cenozoic sand deposits on Ol’khon Island have been performed. It has been shown that their main source is represented by Early Paleozoic igneous and metamorphic complexes of the Ol’khon Terrane of the Central-Asian Mobile belt and Late Carboniferous–Early Permian granitoids of the Angara–Vitim batholite. Sands from the source were transported over a distance of no less than 100 km. It is supposed that it was effectuated by strong air flows, over the ice on the Lake Baikal in particular.

The results of U–Pb dating of detrital zircons extracted from rocks of the Ai Formation are presented. A provenance-signal of a local source with an age of about 2.07 Ga has been documented, and the effect of the Ordovician magmatic episode on the sedimentary sequence has been revealed.

The concentrations of seven heavy metals (HMs) in tissues of bivalve mollusks of the families Unionidae (genera Ensidens, Scabies, Kunashiria) and Cyrenidae (genus Corbicula) and from four natural lakes located on the eastern slope of Sikhote Alin (Primorskii krai, Russian Far East) the Mekong River delta (Vietnam) were determined. It was established that the HM concentrations in the bivalve mollusks studied, inhabiting unpolluted water reservoirs, are specific for every family and do not depend on the geographical positions of the lakes. They decrease in the following order: Mn > Fe > Zn > Cu > Ni > Cd > Pb for Unionidae, and Fe > Zn > Cu > Mn > Ni ≥ Cd > Pb for Cyrenidae (Corbicula). It is likely that deviations from the revealed sequence are due to anthropogenic pollution of lakes with some metals or the occurrence of a natural geological anomaly.

Kyanite gneiss from the “New Barchinsky” locality (Kokchetav Massif) was studied in detail. This rock is characterized by zonal distribution of the C and SiO₂ polymorphs in kyanite porphyroblasts: (1) cores with graphite and quartz inclusions; (2) clean overgrowth zone with inclusions of cuboctahedral diamond crystals. The Raman mapping of SiO₂ polymorphs originally showed the presence of an association of disordered graphite + coesite “prohibited” in HT diamond-bearing rocks. Graphitization of diamond is the only likely mechanism of the disordered graphite formation in HT diamond-bearing rocks. However, the absence of disordered graphite in association with diamond in kyanite porphyroblasts from kyanite gneiss from the “New Barchinsky” locality eliminates the process of diamond graphitization at the retrograde stage. Most likely, crystallization of disordered graphite occurred at the retrograde stage from the UHP C–O–H fluid.

A comparison of the lithological–geochemical parameters for the deposits of the Dalnetaiga series of the Bodaibo synclinorium (the Buzhuikhta and Khomolkho formations) and the Olokit structural-formational zone (the Itykit and Ondok formations), hosting polymetallic deposits (Kholodnin, Ioko-Rybach’e), along with the obtained geochronological LA-ICP-MS U–Pb age estimates of the Ondok Formation (~600 Ma), indicates their similar stratigraphic position in the Neoproterozoic in Southern Siberia. At the first stage of formation of polymetallic and gold-ore objects, the siderochalcophylic trend is considered to have appeared synchronously in the two structural zones, which could have been caused by the hydrothermal activity in the back-arc basin of the Olokit structure.

Data on the U–Pb (SIMS SHRIMP-II) age (3628 ± 38 and 2845 ± 65 Ma) of zircon from the inclusion of mafic granulite in gneiss–enderbites of the Bug complex in Ukraine are obtained. A zircon age of 3628 ± 38 Ma for the first time has allowed us to identify the occurrence of basic magmatism at the Paleo- and Eoarchean boundary in the Bug region. The age of 2845 ± 65 Ma dates the imposed metamorphism manifested everywhere in the Bug region that led to considerable amphibolization and partial melting of the rock.

The mechanisms of paleodeformations during the time of fluid inflow into the accumulation area of gold ore concentrations were studied for two deposits. It was found that the mechanisms corresponded to seismic mechanisms of the DC- and NDC-types. The key effect of the deformation mechanisms as such on the migration of fluids consists in the formation of different structural and hydrodynamic organization of the ore-forming system depending on the parameters of fluid conditions, as well as in controlling the fluid flow within the accumulation area of ore concentrations.

A mechanism of generation of abnormally high accelerations (>1g, with the maximum of ~3g), recorded during the 2011 Tohoku earthquake (M_w = 9.0), is proposed. Based on the records of vertical groups, soil behavior in near-fault zones is studied to reveal an atypical model: shear moduli increased under string motions, demonstrating strengthening of the soil, then decreased. This phenomenon can be explained under the supposition that soils suffered some additional effect. The shapes of accelerograms show a decrease in the duration and an increase in the intensity of strong motions with distance from the source, possibly indicating superposition of seismic waves and formation of a shock wave by a rapidly moving source (a tip of the crack propagating in the source).

Continental runoff, inflowing to Arctic waters, is estimated by the use of isotope and hydrophysical tracers. This is quite a complicated task, because desalinated waters freeze. The existing model of three-component mixing [1] deals only with the input of melted sea ice, thus limiting its utility in zones where ice is intensely formed. A new mixing-modification model is proposed. The effect of the model is illustrated by data from the Laptev Sea shelf, which is affected by the Lena River runoff. Modification of these waters is manifested by an excessive increase in salinity in relation to the oxygen isotope composition, which is determined by the mixing of waters of the Lena River with waters of the Arctic basin. The model considers the water modification owing to the formation and removal of ice.