Vol 488, No 1 (2019)

A mineralogical-geochemical study of globular phyllosilicates (GPS) of the glauconite-illite series of the Dolgokta Formation from the stratigraphic well Chunkinskaya Well 282 was conducted, and their Rb–Sr age was determined. The suitability of the mineral for geochronological studies was estimated based on the Mössbauer spectroscopy data and the model of cation distribution in the octahedral sheet of GPS. The mineralogical and crystallochemical characteristics indicate epigenetic defects in the glauconite crystal structure; therefore, its Rb–Sr isochronous age (1300 ± 7 Ma) is “rejuvenated” and reflects a partial recrystallization event. The ⁸⁷Sr/⁸⁶Sr ratio in dolomites of the Dolgokta and Kuyumba formations varies from 0.70602 to 0.72230 and thereby confirms the epigenetic recrystallization of rocks. The model Rb–Sr age of glauconite, which was estimated taking the enrichment in radiogenic ⁸⁷Sr into account, is within 1340–1400 Ma. The age estimate defines the upper limit of the stratigraphic distribution of the Mesoproterozoic fossil Tappania that was found in the Yurubchen and Dolgokta formations of the Baikit Anteclise.

A zonal igneous areal appeared at the western end of the Mongol–Okhotsk Belt in the Early Mesozoic. Its central part is comprised of the Khentei–Daurian giant batholith, which is framed on its north and west by riftlike structures with manifestations of bimodal and alkaline granite magmatism. Geochronological studies of the Choyr and Gal-Shara massifs of peralkaline granites, belonging to the North Gobi (southern) border of the batholith, are carried out. The ages of the former and latter are 215 and 213 Ma, respectively. It is shown that associations involving alkaline igneous rocks are fairly well developed in the North Gobi zone and controlled by NE-trending faults and grabens. Thus, it is established that the zonal magmatic area was formed under a specific regime. In its central part, which corresponds to the zone of the Mongol–Okhotsk suture, anatexis and batholith-formation processes took place, while the periphery was involved in rifting. The data obtained indicate the closure of the western part of the Mongol–Okhotsk trough before the formation of the zonal magmatic areal. The structure of the magmatic areal was determined by the mechanisms of the plume–lithosphere interaction between the collisional suture (anatectic melting zone) and its less tectonically strained framing (rifting zones).

Based on the first results of massive U–Pb dating of detrital zircons from the basal deposits of the Upper Precambrian section in the Subpolar Urals, their age is determined, and the lower age limit for the deposition of the Timan continental margin of the Baltic is substantiated with consideration of the data obtained earlier.

The geochronological and geochemical parameters of the Raduga muscovite–fluorite–euclase–beryl deposit, located within the Kizir–Kazyr zone of rare-metal magmatism, were determined. In contrast to other deposits and ore occurrences located in this zone and represented by alkaline granites enriched in rare-metal mineralization, the formation of the Raduga deposit is associated with the metasomatic transformations of carbonate rocks. The age of this deposit, estimated by ⁴⁰Ar/³⁹Ar dating of muscovite fromberyllium fluorite–muscovite greisens, is 469.3 ± 4.5 Ma. It corresponds to the age of the ore-bearing alkaline granites. The dykes developed within the deposit are similar in composition to those within rare-metal alkaline–granite massifs, one of which is located a few kilometers from the deposit. The character of the Be–Li ore mineralization in the Raduga deposit is in good agreement with the geochemical specialization of the Early Paleozoic Kizir–Kazyr metallogenic zone. The revealed features of the relationship between the Raduga deposit and rare-metal deposits confined to alkaline granites suggest a variety of mechanisms involved in the formation of rare-metal deposits of the Kizir–Kazyr metallogenic zone. Thus, it allows us to expand the approaches for prediction and exploration of rare-metal deposits in the region.

The ⁴⁰Ar–³⁹Ar dating of mica from schists and blastomylonites, sampled within the limits of a fault that separates the Eastern zone of the Middle Urals, sinking beneath the sedimentary cover of the West Siberian Plate, from the structures located to the west of this plate, in the exposed part of the Urals, has shown that the final phase of deformations was represented by sinistral strike-slip faults trending submeridionally with an age of 251 Ma. The deformations studied virtually exactly coincide in time with the formation of submeridionally oriented grabens in the basement of the West Siberian Plate.

This data on the age of metamorphism of rocks of the Yelabuga zone and the geochronological data on detrital zircon from paragneisses of the same zone are presented, and their correlation with the ages of rocks from the Middle Volga megablock is made. The rocks of the Yelabuga zone and Middle Volga megablock have similar geochemical characteristics and degrees of metamorphism, but demonstrate the following differences: Paleoproterozoic metamorphism was clearly expressed in the studied rocks of the Yelabuga zone, which contrasts to rocks of the Middle Volga megablock, where no metamorphism of this age is manifested. The study of the U–Pb isotopic system in external zones of zircon crystals from the Yelabuga deformation zone suggests that rocks underwent two stages of metamorphism, 1.99 and 1.95 Ga ago.

The Neoarchean subalkaline magmatism of the Keivy structure is manifested by the emplacement of the latite–monzonite–granite (LMG) volcano-plutonic association. The measured ¹⁴³Nd/¹⁴⁴Nd ratio in rocks is 0.511061–0.511365; the values of model ages fall within the interval of 3.14–3.21 Ga with εNd₍₂₆₇₀₎ varying from 2.2 to –1.3. The initial ¹⁷⁶Hf/¹⁷⁷Hf ratios in zircon are within the range of 0.280950–0.281069, and composition data points make up a field in the region of the evolutionary trend of the chondritic uniform reservoir. As based on isotope and geochemical data, the protoliths of all rocks are assumed to be basic. In terms of the εHf(T) value, the data points of the zircon composition fall within the domain of the crust with ¹⁷⁶Lu/¹⁷⁷Hf = 0.015 and an age of 3.0–3.3 Ga. This suggests that the parental melts were probably formed predominantly from material that spent a long time in the crust. The parental melts of the LMG association presumably formed as a result of the melting of metasomatically altered basic rocks during the intrusion into the lower crust of basaltic plutons, which were parental for the rocks of the dyke suite and gabbrolabradorite intrusions in the upper crust.

The isotopic composition of the natural waters of Eastern Transbaikal is studied. It is established that the water of the soda lakes is more enriched in oxygen-18 than in deuterium. It is shown that the enrichment of the salt-lake waters in heavy isotopes occurs not only due to the evaporation process, but also due to water–rock interaction. The participation of the aluminosilicate hydrolysis reactions in the fractionation of oxygen is confirmed by the direct dependence of the magnitude of the oxygen shift on pH, the value of which depends on the degree of such interaction.

This study presents the first data set of sulfur isotope compositions of primary Ru–Os sulfides, represented by laurite (RuS₂) – erlichmanite (OsS₂) series, within a primary platinum-group mineral (PGM) assemblage derived from the Verkh-Neivinsky dunite-harzburgite massif, a typical example of the mantle ophiolite association at the Middle Urals. The S-isotope signatures of Ru–Os sulfides studied are consistent with derivation of the ore material from a mantle source.

The U, Th, and ⁴He contents of meliphanite correspond to an age of metamorphism (1800 Ma) indicating good preservation of radiogenic ⁴He in mineral but contradicting the experience of U–Th–⁴He dating. For the analysis of this result, we studied preservation of ³He, which was found to be very low (~2%). The ^3,4He isotopes occur in radiation tracks, the intersection of which with cleavage planes provide for their migration from the mineral. Thus, ⁴He originated from U and Th decay should be completely lost. Meliphanite entraps He, which probably occurs in specific volumes of its crystal structure. Extraction of He isotopes from meliphanite upon vacuum heating supports this conclusion. Application of only one U–Th–⁴He system for dating (as often applied in thermochronology) may yield erroneous results. Identification of the origin of He in minerals requires using both isotopes (³He and ⁴He).

Estimates of the contribution of anthropogenic and natural greenhouse gases to the atmosphere from the territory of Russia to global climate change under different scenarios of anthropogenic emissions in the 21st century are obtained. It is shown that the consideration of the changes in climate conditions can strongly affect the indicators of impacts of different greenhouse gas emissions on the climate system, especially over long time horizons. In making decisions, it is necessary to take into account that, with respect to the planning horizon, the role of natural flows of greenhouse gases into the atmosphere from the terrestrial ecosystems can change. Currently, in the Russian regions, CO₂ uptake by terrestrial ecosystems decelerate global warming, and their CH₄ release into the atmosphere accelerate it. In this case, the general effect of natural fluxes of these greenhouse gases from the Russian regions under modern conditions foster deceleration of warming. The role of this effect decelerating warming will grow in the first half of the 21st century, and after reaching the maximum, which depends on the scenario of anthropogenic emissions, it will decrease by the end of the century under all scenarios of anthropogenic impacts considered due to the growth of natural emissions of CH₄ and a decrease in the absorption of CO₂ by the terrestrial ecosystems.

The saltating particle aleurite mode has been discovered in the wind–sand flux over a desertified area. The approximation of the measured saltating particle distribution was found using two lognormal distribution functions. In the wind–sand flux, the countable concentrations of aleurite and sand particles depend differently on the wind velocity in the atmospheric surface layer.

Based on “Catalog of earthquakes in the Baikal Region” (52700 earthquakes of representative energy classes K_P > 8, 1964–2013) at the angular sector of azimuthal analysis being q = 10° (±5 from azimuth α), quasilinear chains of earthquakes (M = 2143) were distinguished. As a result, the basic laws of the space–time and energy distribution of these chains in the lithosphere of the Baikal Rift Zone (BRZ) were established. The maximal quantity of chains was distinguished among weak earthquakes: a number of chains decreases as K_P grows following the law of frequency logM = f(K_P) is sloped at –0.48. Azimuths 50°–60° and 240°–260° correspond to the orientation of main seismogenic faults and the epicentral field in the BRZ. In space-time distribution of chains are observed maximum corresponding to high density epicenters and earthquake flow rates. In order to study seismicity migration, the index of migrating seismicity activity (ISMA), which is characterized at a given level of significance the seismicity migration/pseudomigration ratio has been used. The maps of the ISMA distribution over the territory and graphs of ISMA annual variations were constructed. The results obtained indicate a direct relationship between migrating seismicity in the BRZ and the locations and activations of rifting attractor structures (RAS).

A continuous peat bog section from a barely accessible mid-mountain area in the northwestern Baikal region has been obtained for the first time. The materials were studied by methods such as pollen–spore analysis, analysis of plant cell remains, and radiocarbon dating (calibrated data). The smallest peat accumulation rates in East Siberia during the Holocene are revealed. In accordance with the calculated peat accumulation rates, the time resolution is 100 years in the lower part of the section, it is while up to 800 years in the upper one. Six local palynozones and five botanic zones have been distinguished using factor analysis. The vegetation cover changes and environmental moisture conditions for the last 7670 years are reconstructed. The altitude of the forest line is specified for the first time in a quarter of a century.

The geography of emerging and reemerging natural-focal diseases on the territory of Russia is considered. The data on the distribution and features of epidemic manifestation of eight model infections (ixodid tick-borne borreliosis, tick-borne encephalitis, hemorrhagic fever with renal syndrome, tularemia, leptospirosis, West Nile fever, Crimean hemorrhagic fever, and Astrakhan rickettsiosis fever) from different groups of emerging diseases are presented. The risk of exposure to these infections among the population in the European part of Russia is assessed, and they are mapped within the natural borders (biomes).

The vertical isotopic profile of the ice core of a Messoyakha-1 bulgunniakh (pingo)—was obtained. The pingo is situated at 68°30′32″ N, 79°59′53″ E, in the southern part of the Gydan Peninsula within the Middle Messoyakha swell. No significant variations were registered in the isotopic composition of the pingo ice core: δ¹⁸О varied from –14.98 to –16.60‰ and δ²Н varied from –117.9 to –122.8 ‰. This small range of values probably resulted from intense heaving and rather rapid formation of the pingo. Based on the features of the pingo, it can be assumed that initially there was a lake of 0.5 km length and 0.3 km width at this site. Then, the water drained into a nearby river, the lake began to dry out, and the khasyrey (alas), which occupies most of the former lake area, was formed. The pingo itself arose during the freezing of the alas under its gradual drying out.

The results of the field experiments on the directional development of local biocenoses based on bottom biostations situated in the areas with a high anthropogenic load in the Northern and Middle Caspian are presented. The structural and functional characteristics of the local communities compared to background indicators are studied; the biodiversity and informativeness of the communities as objects of monitoring and bioindication are assessed. The prospects of using the methodology of directional development of biocenoses on artificial substrates for optimization and improvement of the marine environment in the areas of active development of hydrocarbon resources on the shelves of Russia are discussed.