Volume 470, Nº 2 (2016)
- Ano: 2016
- Artigos: 26
- URL: https://journals.rcsi.science/1028-334X/issue/view/11838
Geology
Regional anomalies of hydrocarbon fluid saturation as a new source of data on promising oil and gas deposits in the Caspian shelf
Resumo
This paper analyzes the ratio of local and regional anomalies of fluid saturation identified in the southern margins of the Eastern European Platform by remote fluid indexation. A characteristic feature of this area is the very low background values in the initial field, i.e., local anomalies reflecting the deposits. Regional anomalies are mainly related to oil and gas accumulation zones. In the Middle Caspian areas studied, the regional field of the fluid saturation index is the background for local anomalies. We made an attempt to justify the hydrocarbon migration and generation zones as anomaly-forming zones of the regional anomalies. The correlation of oil and gas accumulation zones with the regional field anomalies was noted.
Early Cretaceous sea level fluctuations in the eastern part of the East European Platform
Resumo
The quantitative sea-level curve in the eastern part of the East European Platform during the Early Cretaceous first compiled for this region is based on the results of analysis of the corresponding deposits and the bathymetric distribution of benthic foraminifers in their sections. This quantitative curve is correlated with the sea-level curve constructed for central areas of the East European Platform [9]. According to [9], the basin in the central part of the platform was as deep as 110 m, while in its eastern areas the depth amounted to 350 m. It is revealed that tectono-eustatic cycles defined previously in the central part of the platform and cycles (megasequences) in its eastern areas are asynchronous and are characterized by different orders. Such asynchrony is determined by the different tectonic trends in these regions during the Early Cretaceous.
Primary divisibility of the protolithosphere and current tectonic divisibility of lithospheric blocks: New reconstructions
Resumo
The layer forming the Earth’s solid cover is considered to be a uniformly cooling mantle body of low viscosity involved in the convection process. Its cooling is accompanied by the formation of Rayleigh–Benard cells transformed into primary blocks. Their dimensions and dynamics in the subsequent evolution of the Earth’s lithosphere were repeatedly disturbed by superglobal geodynamic cycles involving changes in the area and dynamics of the blocks, some of which were partially absorbed by the mantle, while others were generated for the first time up to the current state. The variably ranked lithosphere blocks transformed into linear dimensions were arranged in a logical series of lithosphere destruction: from convection of the cooling Earth and initial block divisibility of the protolithosphere to its recent plate tectonics and intensive variably ranked fragmentation and fracturing of the plates under the conditions of solid body fragmentation. Convection in the mantle is a genetic endogenic source of the first protolithosphere divisibility. Megablock and subsequent lithosphere divisibility are consistent with the process of crushing of a solid body.
Sources of Paleozoic granitic rocks and isotopic heterogeneity of the continental crust of the Aktau–Dzhungar microcontinent, Central Kazakhstan
Resumo
Several generations of Paleozoic granitic rocks are studied with Sm–Nd isotopic methods in the northwestern part of the Aktau–Dzhungar microcontinent of Central Kazakhstan (Atasu–Mointy divide). The initial Nd isotopic composition of the granitic rocks varies in a relatively narrow range from–0.1 to–3.5ε; the Nd model ages are also similar (1.11–1.46 Ga). These results indicate that the crustal source of all the Paleozoic granitic rocks of the region had similar composition and, probably, age. It is shown that the tNd(DM) values of the Paleozoic granites reflect different proportions between ancient and juvenile material in the crustal source.
The isotopic–geochronological age of trap formation rocks in the sedimentary section of the Baikit anteclise
Resumo
The Lower Cambrian Usol’e Formation in the Kamov arch of the Baikit anteclise includes stratiform intrusions confined to several levels. According to isotopic‒geochronological investigations, the age of stratiform intrusions composed of olivine dolerites is estimated to be 256.0 ± 3.2 Ma.
Igneous rocks of the West Sakhalin Terrane of Sakhalin Island
Resumo
It has been determined that the Rozhdestvenka Formation of the West Sakhalin Terrane composed of Late Mesozoic igneous rocks is a fragment of the accretionary prism of the Rebun–Kabato–Moneron–Samarga island-arc system. Volcanic eruptions, as well as destruction of the Rebun–Kabato–Moneron–Samarga island-arc and the East Sikhote-Alin volcano plutonic marginal continental belt, were the sources of pyroclastic and clastic material entering the sedimentary basin, where the Pobedinsk and Krasnoyarka suites of the West Sakhalin Terrane were formed.
Middle Paleozoic kimberlite magmatism in the northeastern Siberian craton
Resumo
The mineral chemistry and crystal morphology of kimberlite pyropes from the Billyakh River placer in the northeastern Siberian craton are characterised in terms of the placer history. The pyropes bear signatures of chemical weathering (dissolution), presumably in a Middle Paleozoic laterite profile, and therefore were originally hosted by Middle Paleozoic kimberlites. The broad occurrence of placer pyropes with lateritic dissolution signatures points to the presence of Middle Paleozoic diamond-bearing kimberlites in the study area.
Analysis of the productivity of gold deposits of Amur province
Resumo
By the amount of extracted placer and primary gold (~1300 t), Amur province is one of the major gold provinces of Russia. Its numerous placers yielded almost 1132 t Au in contrast to ~180 t from primary deposits. The central part of the province is most productive for placer and primary gold in comparison with the periphery. Native gold from placers has moderately high and high fineness, and its composition corresponds to that of gold from dominant gold–quartz and gold–quartz–sulfide deposits and occurrences. The preponderance of placer gold in gold production indicates significant prospects for discovery of new gold deposits.
Finds of economic platinum in ores from the South Khingan Mn deposit
Resumo
Platinum is revealed by the authors in the Mn ores from the South Khingan deposit of Malyi Khingan. Its quality (grain size, aggregates) and amount are of economic interest. Platinum has higher contents of Fe, Cu, Mn, Ni, Os, and other metals. The Pt potential is related to carbonaceous metasomatites, which replaced fluidolites.
Geochemistry
Geochemical features of the utilization of buried wastes of the Tyrnyauz Tungsten–Molybdenum Plant using acid leaching
Resumo
The decontamination of buried wastes of the Tyrnyauz Tungsten–Molybdenum Plant is complicated by the geochemical features of the waste composition: low sulfide and high carbonate content, polyelemental composition, and considerable amounts of technogenic admixtures (kerosene, oils, soda, and soluble glasses). These circumstances result in sufficient complication of the suggested technology of waste treatment, including the sulfuric-acid leaching and separate sorption recovery of hazardous and useful elements from the working solution.
REE distribution in zircon from reference rocks of the Arctic region: Evidence from study by the LA-ICP-MS method
Resumo
The results of the LA-ICP-MS analysis of the concentrations of REEs, U, Th, and Hf in zircon from Paleo- and Neoarchean reference rocks of the Kola region (garnet–amphibole gneiss, basic and acid granulites, and granite pegmatite) are reported. A new methodology of the study of accessory zircons has been validated and modified. The accuracy of the results is confirmed by analysis of standard zircons Temora 1 and 91 500 and by comparison with the data obtained in other laboratories.
Homogenization of carbonate-bearing microinclusions in diamond at P–T parameters of the upper mantle
Resumo
The staged high-pressure annealing of natural cubic diamonds with numerous melt microinclusions from the Internatsional’naya kimberlite pipe was studied experimentally. The results mainly show that the carbonate phases, the daughter phases in partially crystallized microinclusions in diamonds, may undergo phase transformations under the mantle P–T conditions. Most likely, partial melting and further dissolution of dolomite in the carbonate–silicate melt (homogenization of inclusions) occur in inclusions. The experimental data on the staged high-pressure annealing of diamonds with melt microinclusions allow us to estimate the temperature of their homogenization as 1400–1500°C. Thus, cubic diamonds from the Internatsional’naya pipe could have been formed under quite high temperatures corresponding to the lithosphere/asthenosphere boundary. However, it should be noted that the effect of selective capture of inclusions with partial loss of volatiles in relation to the composition of the crystallization medium is not excluded during the growth. This may increase the temperature of their homogenization significantly between 1400 and 1500°C.
Coesite inclusions in diamonds of Yakutia
Resumo
The results of the study of diamonds with inclusions of high-pressure modification of SiO2 (coesite) by Raman spectroscopy are reported. It is established that the octahedral crystal from the Zapolyarnaya pipe is characterized by the highest residual pressure (2.7 ± 0.07 GPa). An intermediate value of this parameter (2.1 ± 0.07 GPa) was obtained for a crystal of transitional habit from the Maiskaya pipe. The minimal Raman shift was registered for coesite in diamond from the Komsomol’skaya–Magnitnaya pipe and provided a calculated residual pressure of 1.8 ± 0.03 GPa. The residual pressures for crystals from the placer deposits of the Kuoika and Bol’shaya Kuonamka rivers are 2.7 ± 0.07 and 3.1 ± 0.1 GPa, respectively. Octahedral crystals were formed in the mantle at a higher pressure than rhombododecahedral diamonds.
Geodynamic background for large-scale mineralization in the southern environs of the Siberian Craton in the Proterozoic
Resumo
The geodynamic position of the productive Kevaktinskii and Dal’netaiginskii stratigraphic units with Au–U mineralization is considered within the Baikal–Patom highland. The Au–U specialization of rocks of the Kevaktinskaya Group results from its formation in the environments of the passive continental margin with introduction of the juvenile material related to riftogenesis and further collision, whereas the same specialization of the Dal’netaiginskaya Group is explained by exhalation activity in the back-arc spreading zone. The formation of most of the Au and U large-scale deposits within the southern environs of the Siberian Craton was controlled by Paleozoic oogenesis upon closure of the Paleoasian Ocean.
Uranium in the mineralized lakes of Altai Krai
Resumo
Data on the physicochemical properties (pH, Eh, salinity) and content of U and other trace elements (As, Li, B, Br, I, Sr) are provided for the mineralized lakes of the Kulundinskaya steppe of Altai Krai. The sodic lakes of the region are characterized by higher U238 contents (up to 4 mg/l). The U contents in the lake waters are positively correlated with the sum of carbonate and hydrocarbonate ions and the pH of waters and are negatively correlated with salinity. These data confirm the presence of an economic U-bearing zone of the ground reservoir oxidation located along the eastern slope of the Platovskoe uplift in the northwestern direction along the boundary with Kazakhstan.
Sedimentary complexes of the cover of the Dzabkhan continental block: Different sedimentary basins and source areas
Resumo
The geochemical and Sm–Nd isotope characteristics of Late Precambrian and Early Cambrian sandstones previously related to the sedimentary cover of the Dzabkhan continental block are reported. It is established that the Riphean and Vendian sedimentary rocks of the Ul’zitgol’skaya and Tsaganolomskaya Formations were accumulated within the Dzabkhan continental block as a result of recycling of the terrigenous deposits formed at the expense of destruction of basement rocks and younger granite. The formation of terrigenous rocks of the Bayangol’skaya Formation after a gap in sedimentation occurred in the sedimentary basin, where only the Late Riphean formations of the juvenile crust, probably of the Dzabkhan–Mandal block were the sources, without the contribution of the ancient crustal material. The Tsaganolomskaya and Bayangol’skaya Formations were formed in different sedimentary basins and cannot be related to the same complex.
Geochemistry of biotite from charnockitoids in the granite-forming series (Nimnyr Block of the Aldan Shield)
Resumo
The geochemical evolution of biotite (Bt) from garnet-bearing associations in the granite-forming series of the Nimnyr Block (Aldan Shield) is considered. The series includes the primary rock (gneiss or basic rock), autochthonous enderbite- or charnockite-gneiss (Lc1), migmatitic leucosome (Lc2, Lc4), and paraautochthonous charnockite (Lc3-ch1) and (Lc5-ch2 → grn). Bt in each series is characterized by an individual, significant difference in the concentrations of Ti, V, Cr; rarely Al, Fe, Mg, and Rb; and very rarely La, Ce, Nd, and Gd. The uniform trend of evolution of Bt compositions in the series was established for Al, KAl, (K + Na)/Al, rarely for Mg, Ti, and К. In contrast to the series with ch2, Bt becomes enriched in LREEs from autochthonous Lc1 to allochthonous Lc2 and Lc3. The different compositional variations of Bt in relation some minor elements is explained by the different composition of the material, which underwent melting, temperature variations (from 820 to 750°C), and changes in pH of the mineral-forming medium.
238U and 235U isotope fractionation upon oxidation of uranium-bearing rocks by fracture waters
Resumo
The variations in 238U/235U values accompanying mobilization of U by fracture waters from uranium-bearing rocks, in which U occurs as a fine impregnation of oxides and silicates, were studied by the high-precision (±0.07‰) MC–ICP–MS method. Transition of U into the aqueous phase in the oxidized state U(VI) is accompanied by its isotope fractionation with enrichment of dissolved U(VI) in the heavy isotope 238U up to 0.32‰ in relation to the composition of the solid phases. According to the sign, this effect is consistent with the tendency of the behavior of 238U and 235U upon interaction of river waters with rocks of the catchment areas [11] and with the effect observed during oxidation of uraninite by the oxygen-bearing NaHCO3 solution [12].
Geophysics
The Uryakh ore field (NE Transbaikalia): Formation of structural assemblages in the centroid-type seismic regime
Resumo
Syn-ore centroid type deformations that produced unusual structural assemblages are identified in the Uryakh ore field. The regularities of the deformation process comparable to a mechanism of the centroid-type seismic focus are established. The results of studying fluid inclusions suggest that the pressure—temperature parameters of the system correspond to conditions typical of the seismic regime. A model of formation of structural assemblages in a centroid-type dynamic regime with the participation of fluids is proposed for the first time.
Unified scaling law for earthquakes in Crimea and Northern Caucasus
Resumo
This study continues detailed investigations on the construction of regional charts of the parameters of the generalized Guttenberg–Richter Law, which takes into account the properties of the spatiotemporal seismic energy scaling. We analyzed the parameters of the law in the vicinity of the intersections of morphostructural lineaments in Crimea and Greater Caucasus. It was shown that ignoring the fractal character of the spatial distribution of earthquakes in the southern part of the Russian Federation can lead to significant underestimation of the seismic hazard in the largest cities of the region.
Observations of atmospheric methane and its stable isotope ratio (δ13C) over the Russian Arctic seas from ship cruises in the summer and autumn of 2015
Resumo
The results of experimental measurements of atmospheric methane concentrations and its isotopic composition in the Russian Arctic seas in the summer and autumn of 2015 are discussed. The Keeling plot method and inverse number simulation were used for revealing the factors responsible for elevated methane concentrations over the sea surface. Its maximum concentrations (up to 2050 ppb) were measured over the Kara and Laptev seas, as well as in the port area of Arkhangel’sk. It is shown that tundra and bog ecosystems of Siberia serve as the main sources of methane in the measurement zone (except for the area adjacent to large ports). As a whole, the share of methane from microbiological sources is as high as approximately 43% of the total methane concentrations along the ship route.
Precursors of dynamic failure on a tectonic fault
Resumo
A new method for controlling the dynamic shear stiffness of interblock contact during stick-slip is proposed. This method enables us to reveal changes in the mechanical properties of the contact long before the macroscopic slip will be recorded. In the experiments conducted, the time of precursor manifestation was about 1/3 of the duration of the “seismic cycle.”
Characteristic scale of heterogeneity of seismically active fault and its manifestation in scaling of earthquake source spectra
Resumo
Previously, similarity of source spectra of Kamchatka earthquakes with respect to the common corner frequency fc1 and the expressed deviations from similarity for the second fc2 and the third fc3 corner frequencies were revealed. The value of fc3 reflects the characteristic size Lis of fault surface; correspondingly, Lis ≈ vrTis, where vr is the rupture speed and Tis ≈ 1/fc3 is characteristic time. The estimates of fc3 are used for normalizing fc1 and fc2. In this way one obtains dimensionless rupture temporal parametres τ1 and τ2 and can further study the dependence τ2 (τ1). The growth of a rupture is considered as a process of aggregation of elementary fault spots of the size Lis. The dimensionless width of the random front of aggregation is on the order of τ2. The relationship τ2 (τ1) approximately follows power law with exponent β. The estimates of β derived from earthquake populations of Kamchatka, USA and Central Asia (β = 0.35–0.6) agree with values expected from the known Eden’s theory of random aggregation growth and from its generalizations.
Geography
δ18O and δD variations in Holocene massive ice in the Sabettayakha river mouth, northern Yamal Peninsula
Resumo
The conditions of formation of massive ice near the South Tambey gas-condensate field in northern Yamal Peninsula are studied. It is shown that massive ice bodies up to 4.5 m thick occur in the Holocene deposits of the high laida and the first terrace. Therefore, they cannot be the remains of glaciers; they are ground ice formations. All three types of massive ice have quite various isotopic compositions: the values of δD range from–107 to–199.7, and δ18O from–15.7 to–26.48‰. Such a significant differentiation in isotopic composition is a result of cryogenic fractionation in a freezing water-saturated sediment. The most negative isotope values are even lower in this Holocene massive ice than in the Late Pleistocene ice-wedge ice of Yamal Peninsula.
Oceanology
A condition for the existence of quasi-periodic nonlinear internal waves in the ocean shelf zone
Resumo
Free internal gravity waves, which are typical of the shelf ocean zone are studied. A necessary condition for the existence of nonlinear wave disturbances quasi-periodic in time in a continuously stratified sea with variable depth H is found in the quasistatic and the “hard cap” approximation with respect to dissipative factors and latitudinal variation in the Coriolis parameter. The obtained assessment is equivalent to the condition obtained within the framework of linear theory for the case of the f-plane and a constant depth H.