Том 486, № 2 (2019)

This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the Tokur terrane. It has been established that the grains of detrital zircons from the meta sedimentary rocks of the Tokur and Ekimchan formations have a similar age distribution, which indicates the similar (or equal) age of these formations. The youngest zircons in these rocks has a U–Pb age of 326–323 Ma, which determines the lower age limit of the protolith of the rocks. The upper age limit of the formations corresponds to 254–251 Ma, which is the age of the Late Permian granitoids intruded into these formations. The main sources of zircon in the meta sedimentary rocks of the Tokur terrane are the igneous and metamorphic massifs of the southeast framing of the North Asian Craton. The Tokur terrane can be considered as a fragment of the Paleozoic accretionary complex, formed near the southeastern margin of the North Asian Craton.

This paper considers the compositions of ferromanganese crusts and nodules (FMCNs) growing on bedrock of Mendeleev Rise, collected in 2016 using a research submarine. The concentrations of Fe, Mn, Co, Ni, Zn, Cu, Cr, and Pb are measured in the collected FMCNs. Analysis of the variations in the contents of ore elements in the studied FMCNs shows that these changes are determined by the following factors: (1) the relative heights of submarine relief (higher relief is characterized by higher concentrations of Co and Ni); (2) substrate character (if it is a tuff, then its alteration provides additional Mn and Zn enrichment of FMCNs); (3) participation of bottom ooze (in the case of extensive contact of substrate fragments with ooze under the influence of pore waters, FMCNs become enriched in elements such as Mn, Co, and Ni); (4) chemical properties of elements (Mn hydroxides concentrate Co and Ni, whereas Fe hydroxides host Cu and Zn).

Rocks of Early Precambrian age have been established in many polymetamorphic complexes of the Urals. However, there is no doubt that only two polymetamorphic complexes (Taratash and Aleksandrovsk), located on the western slope of the Urals, belong to the Archean–Paleoproterozoic sequence. They are surrounded by Lower Riphean weakly metamorphosed deposits. The reliable age data obtained for these deposits make it clear that the age of their metamorphism is Early Precambrian. Thus, there are different interpretations of the Early Precambrian dates obtained for other polymetamorphic complexes of the Urals (predominantly, Late Precambrian and Paleozoic ages). Therefore, their link with the Lower Precambrian sequence has been disputed by many researchers. Based on the results of mass U–Pb dating of metamorphic zircons from the gneisses of the Nyarta polymetamorphic complex of the Subpolar Urals and taking into account the age dates available, the Paleoproterozoic age of the earliest stage of metamorphism (2127 ± 31 Ma) was substantiated for the first time. This gives us grounds to say that the Nyarta complex, as well as the Taratash and Aleksandrovsk complexes of the Southern Urals, belong to the Lower Precambrian formations involved in the structure of the Uralides.

New finds of brown bear (Ursus arctos L., 1758) fossil remains from the territory of Yakutia, namely, skulls and mandibular bones, have been investigated. The new finds are exceptionally large: most dimensions of these specimens exceed those of the present-day brown bears of Yakutia and even the maximal parameters of the largest individuals of the present-day Eurasian subspecies U. a. beringianus and U. a. piscator. Analysis of various data showed that giant brown bears had inhabited northern Yakutia during the Karginian interstadial in the Late Pleistocene.

Three groups of diamond crystals that differ in morphology, photoluminescence, infrared absorption, and thermal history were discovered in the Lomonosov deposit. The first group crystals are mostly octahedrons with minor signs of dissolution and a large share of nitrogen in the form of B defects. The crystals of the second type are strongly resorbed dodecahedroids with a small share of B defects. The third group consists of crystals with low-temperature С defects; they are cuboids that are often without traces of resorption, and tetrahexahedroids. These patterns indicate the polygenicity of the diamond in the Lomonosov deposit.

The results of studies of the chemical structure of organic matter in Devonian and Jurassic carbonized wood using IR, ESR, and GC–MS techniques along with elemental analysis are presented. It is shown that the examined samples consist of metamorphism products of natural lignin, which confirms the hypothesis of the key role of lignin in coal formation.

Diamond crystals from the Istok (25 crystals) and Mayat (49 crystals) placers were studied using the EPR, IR, and luminescence methods. The total content of impurity nitrogen in forms of A, B, and C (P1) centers ranges from 50 to 1200 ppm. According to the EPR spectroscopy, the presence of nitrogen C (P1), N₃V and nitrogen-titanium OK1, N3, NU1 impurity centers was established in the investigated crystals. For 18 crystals from the Istok placer, the N3 nitrogen-titanium center was observed in the EPR spectra, but in the luminescence spectra there was no 440.3 nm system, which was previously attributed to the manifestation of the N3 defect. It is more likely that the nitrogen-titanium N3 EPR center corresponds to the electron-vibrational system 635.7 nm, which is observed in the luminescence spectra of these crystals. Crystals from the Istok placer contain the OK1, N3, and NU1 centers, but luminescence attributed to the oxygen-containing centers is absent in the region of 610–670 nm. For the Mayat placer crystals, the reverse situation was observed. The luminescence ascribed to the oxygen-containing centers was detected for 17 crystals, but there were no OK1, N3, and NU1 centers according to the EPR and luminescence. This result contradicts the arguments of a number of authors about the oxygen nature of these defects. For 5 crystals from the Mayat placer, the nickel impurity was registered. This indicates the presence of ultrabasic paragenesis diamond crystals in this placer.

The chemical compositions of garnets from a megacryst association of the Mir kimberlite pipe have been studied. By petrogenic elements, the garnet megacrysts can be classified as high-Ti and low-Cr pyrope. The megacryst TiO₂ contents of the Mir pipe correlate inversely with the MgO and Cr₂O₃ contents. Modeling of the composition of garnets through a fractional crystallization process showed that the most suitable composition of the melts parental for the garnets of the megacryst association is picrite. The composition of garnets crystallized from the kimberlite does not correspond to the composition of the natural garnets from the Mir pipe. The kimberlites contain less Ti, Zr, Y, and HREEs, but are more enriched with strongly incompatible elements (LREEs, Th, U, Nb, Ta, and Ba) than the model composition of the melt suitable for crystallization of the garnet megacrysts.

A model of the behavior of sulfur isotopes in modern hydrothermal isotope systems is suggested. It is accepted that the thermogenic sulfate reduction in the zone of interaction with rocks of the oceanic floor proceeds in a system closed in relation to the fluid. This results in Rayleigh exhaustion in relation to the ³²S isotope. In addition, this model accounts for simultaneous extraction of sulfur from the host rocks; its concentration in the total content of reduced sulfur in the fluid ranges from 0.15 to 0.06 for the submarine systems related to tholeiitic basalt and peridotite, respectively. Application of the model explains the well-known contradictions observed in the study of the sulfur isotope composition of sulfides from the deep-sea structures of the World Ocean.

Physical–chemical simulation of the conditions of hydrocarbon formation at the Erema–Chona oil accumulation (Lena–Tunguska petroleum province) revealed that methane and organic matter accumulates at the basin bottom at the stage of sedimentogenesis (T = 35°C, P = 0.1 MPa). At the stage of diagenesis (T = 60°C, P = 5–10 MPa) (60–100 m depth), during the formation of oil-source rocks, films and drops of oil appear and pentane C₅H₁₂ forms. At the stage of catagenesis, at 250 m depth, hexene C₆H₁₄ forms; at 2000 m, heptene C₇H₁₆; at 3100 m, octane C₈H₁₂; and at 3800 m (T = 90°C, P = 110 MPa), nonane C₉H₂₀. In the period of apocatagenesis and metamorphism at 13–15 km depth (T = 105°C, P = 450 MPa), dodecane C₁₀H₂₂ forms, whereas at T = 200°C undecane C₁₁Н₂₄ appears. With temperature and pressure increased up to 250°C and 490 MPa, respectively, at about 15 km depth, a large group of hydrocarbons forms: liquid ones include the range from dodecane C₁₂H₂₆ to pentadecane C₁₅H₃₂, while solid ones range from hexadecane C₁₆H₃₄ to octadecane C₁₈H₃₈. Finally, when the pressure reaches 850 MPa, at 25 km depth, isoprenoids ranging from nonadecane C₁₉H₄₀ to tetracosane C₂₄H₅₀ appear, as well as other hydrocarbons. Proceeding from the modeling results, it is obvious that hydrocarbon formation at depths down to 25 km cannot be explained solely by any hypothesis of organic or inorganic oil generation. A new sedimentary–migration–igneous hypothesis of oil formation is proposed. Its basic idea is that methane from the bottom of water basins and organic matter act as sources of hydrocarbons down to 3800–4000 m depth, replaced by deep mantle methane at 13–15 and 25 km depth.

The results of experiments on the synthesis of exotic titanates (priderite and yimengite) simulating metasomatic conditions of alteration of the mantle minerals (chromite and ilmenite) are reported. Ba-free Cr-bearing priderite was synthesized for the first time. Experiments showed the possibility of crystallization of this mineral as a product of the reaction of high-Cr spinel and rutile with hydrous–carbonate fluid (melt) under the conditions of the upper mantle. In particular, the experimental data obtained provide an interpretation of the relationships between K‒Cr priderite and carbonate–silicate inclusions in chromites from garnet peridotite of the Bohemian massif. Experimental study of the reaction of chromite and ilmenite with potassic hydrous–carbonate fluid (melt) shows the presence of both titanate phases (priderite and yimengite), the mineral indicators of mantle metasomatism. This provides direct evidence for the formation of yimengite and K‒Cr priderite, as well as other titanates, due to mantle metasomatism of the upper mantle peridotite under the conditions of the highest activities of potassium.

Metarhyiolites are found along with metapelites and metabasites in sedimentary–volcanic sections of Archean greenstone belts of the Kursk block of the Eastern Sarmatia. The age of igneous protoliths of metarhyolites is about 3.12 Ga. A positive value of εNd(3122) = +0.9 for metarhyolite and a model age of TNd(DM) = 3.30 Ga, as well as the age of the inherited zircon grain (3250 Ma), testify to the contribution of a more ancient crustal component in the formation of rhyolite magmas. In terms of the geochemical characteristics, metarhyolites are quite similar to tonalites and trondhjemites of the TTG association of about 3 Ga in age within the framework greenstone belts of the Kursk block. These data confirm the hypothesis of the common geological history of the eastern part of the Ukrainian Shield and the Kursk block during the Mesoarchean.

Multiannual observations (2009–2017) by means of autonomous seiche recorders have been conducted for marine seiches with one second discreteness in the boot basin for harbor fleet of the settlement of Okhotskoe (Sakhalin Island) at the depth of ~2 m beneath ice. The spectral analysis of the data showed the presence of several significant peaks at periods from 2 to 15 s for the moments of strong swell at the sea. These peaks are caused by wave processes, which are generated by nonlinear transformation of the under-ice rippling. Numerical modeling of the reaction of the dynamic system (water area described by Duffing equation) is carried out depending on the parameters of the experimental observations. It is shown (including the Poincaré map) that the amplitude of the external influence greatly affects the transition of the system to chaos.

The eastern boundary of the Siberian Craton was formed as a result of rifting that split the continent late in the Middle Paleozoic. The paleomagnetic data derived from the Middle Paleozoic kimberlites and basites that were formed in the zone of the dynamic effect of the Vilyui paleorift attest to the clockwise rotation of the Aldan terrane relative to the Angara–Anabar terrane during the post-Late Devonian time. The amount of rotation of the terranes increases gradually eastward and reaches 22° on the eastern flank of the Chara–Sinsk dyke belt.

The metal composition of water and bottom sediments of the southern tributaries of Lake Baikal has been studied, and the water migration coefficients have been calculated. A regional zoning scheme is compiled according to the ability to supply a given composition of waters. Significant differentiation of the Baikal waters and its main tributaries by mineralization, the predominant macro-, and trace elements is found. The comparison of coefficients of aquatic migration based on metal composition of waters and sediments shows that the coefficient values calculated for macro elements are close in the southern and main tributaries, and the values calculated for microelements differ sharply. The reason is the presence of sources of solutes (rocks and deep groundwater) with a composition uncharacteristic for the respective landscapes. The contribution of southern tributaries to the macro element composition of the water of Lake Baikal is 7–15%, and the contribution to the micro element composition cannot be assessed due to their much higher concentrations in river waters. The reason for these differences is the migration of trace elements in the form of organic matter, which, due to the extended time of water exchange in Baikal, precipitates or destroys, contributing to the removal of trace elements from the solution.

The background of the conditions causing the formation of corallite crusts, constituted by the fine-fibrous spherulites, is considered. The corallite crusts are the specific form of karstic relief forming in cold climate in an area of perennial cryotic rocks distribution. The scientific interpretation of corallite crusts condensation genesis, being practically absent in scientific literature, is given.

Based on archival data of the Institute of Natural and Technical Systems for the period from 1956 to 2010, the large-scale structure, seasonal variability, and long-term trends of pH variations in the upper 150-m layer of the deep-water part of the Black Sea were analyzed. The spatial climatic inhomogeneities of pH in the surface layer of the open part of the Black Sea are about 0.06 pH units; the magnitude of the average seasonal cycle is 0.05 pH units. In the deep-water part of the sea, low values of pH are observed in the vicinity of the centers of cyclonic gyres, where more acidic waters move upward. A long-term increase in the acidity of waters of the surface layer is observed. Thetrend of pH in this layer is generally conditioned by the increase in the CO₂ content in the lower troposphere and absorption of part of the excess CO₂ by sea water. The increase in the acidity manifests itself in the decrease in pH (at a level of –0.06 pH units per 50 years) in waters of the surface layer. This is close to the estimations for other regions of the World Ocean. However, the intermediate waters are characterized by a negative pH trend, the absolute value of which exceeds more than fivefold the pH trend on the surface. A likely reason for the intense decrease in pH here is the intensification long-term vertical circulation in the intermediate layer of the Black Sea waters, resulting in the ascension of more acidic waters with a typical velocity of ~1 m per year. This can lead to more intense acidification of surface waters in the sea over the next 10 years.