bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent trends of snow avalanche regime in the Central Caucasus (Elbrus region as an example)
Authors: Oleinikov A. D. , Volodicheva N. A.
Published: June 2019

The climate change during cold seasons of 1995–2017 in the Central Caucasus is estimated, and its influence on the avalanche regime is shown. Data on the avalanche releases in the Central Caucasus for the period 1968– 2017 together with observations of high-altitude meteorological stations were used for the analysis. The paper presents estimates of snowiness of the winters and their frequency of occurrence in the area under investigation. The winter snowiness was noted to decrease since the beginning of the 2000s. The last decade of the period was not snowy, especially its series of six winters having very small amounts of snow. It is shown that in the second half of the XX century the heaviest snowfalls took place mostly in Januaries, and they were followed by releases of avalanches with the volumes exceeding 1 million cubic metres. In the early 2000‑ies, intensive January snowfalls were observed later, i.e. during the winter-spring period. In the warmer months March and April, the destructive potential of avalanches was noticeably smaller. In the present time, the warming and decrease of winter snowiness resulted in significant diminution of the avalanche hazard in the region. At the same time, on the background of general warming the certain increase in inter-seasonal variability of air temperature was noted. These changes may be compared to the warming of 1910–1945 when during its warmest phase the Europe suffered with one of the harshest winters in 1941/42. The swing of the «temperature pendulum» indicates that a harsh winter with heavy snowfalls and avalanches with catastrophic consequences may occur on the background of winters with mild and moderate avalanche danger. This is one of probable scenarios in the development of avalanche activity in the Greater Caucasus in the context of the current climate change.
Simulating of snow cover formation by the model of interaction between the land surface and the atmosphere (SWAP)
Authors: Gusev E. M. , Nasonova O. N.
Published: June 2019

In framework of the project «The Earth system Models – Snow Models Intercomparison Project» (ESMSnowMIP), calculations of snow storages were carried out on ten experimental sites organized for longterm monitoring of the snow cover variability in various regions of the globe. The calculation method is based on the physical and mathematical description of heat and moisture exchange processes occurring within the system «ground water – soil – vegetation cover/snow cover – surface layer of the atmosphere», and it is implemented in the form of the model of interaction between the land surface and the atmosphere (SWAP). The model was developed at the Institute of water problems (IWP) of Russian Academy of Sciences. The model makes possible to calculate components of water and heat balances and different characteristics of the hydrological regime of terrestrial ecosystems and river basins having different spatial scales and located in different natural conditions. Good quality of reproduction of the snow storages variability on all considered sites is reached that allows consideration of the SWAP model as one of the best models of the snow cover formation. Thus, the SWAP model has a sufficiently optimal degree of complexity of the algorithm for reproducing the dynamics of snow cover, which is necessary and sufficient in global and regional hydrological models describing formation of the water balance of the land in the cold regions of the planet, and can be used to create scenario forecasts of snow dynamics (as the important part of the cryosphere). This conclusion is verified by the results of using the SWAP model to reproduce long-term variability of snow storages in basins of the River Lena and the River Ob (with its tributary Irtysh) which are the two largest rivers of the Russian Federation. The calculated and measured characteristics of snow cover dynamics for these basins are shown to be in good agreement.
Severity of the present-day climate in the Polar regions of Siberia
Authors: Maksyutova E. V. , Bashalkhanova L. B.
Published: June 2019

Over the period 1981–2015 severe climatic conditions on the North of Siberia (area within 66–162° E above the Polar Circle) were characterized by significant space-time variations of air temperature at the cold period of the year. This conclusion is made on the basis of analysis of observations made about 13 hour of local time. Positive changes in the mean seasonal air temperature were observed here in October–April. The largest rates of air temperature rise with a pronounced gradient to the West were noted in high latitudes, i.e. in Arctic glacial and polar desert landscapes. The change in weather severity which is one of characteristics of the climate discomfort was analyzed by means of the Arnoldi index (TA). This index reflects the combined effect of negative temperatures and stiff wind on the thermal state of the open surface of the human body. Together with the space-time dynamics of the actual TA values, important values of TA are its threshold values (more than 30 and more than 45 units) which determine a degree of discomfort. Duration of these periods, limiting a possibility of a person's stay in the open air, is also extremely important as well. In recent decades (1981–2015), the spatial differentiation of the number of days (from 80 to 160) limiting the human’s stay in the open air reflects in the main fluctuations of the air temperature and wind regime in polar landscapes. Slight warming (a rise of the air temperature) and small wind speed variability during the period from October to April in 1981–2015 resulted in a certain decrease in the index of weather severity in relation to the period 1966–1980, since the last one did not did not go beyond limit of the interannual variability. Despite the stable increase in the air temperature in 1981–2015, no tendency to reduction of the number of days limiting human’s stay in the open air was noted. The duration of this period for 1981–2015 is similar to that observed in 1936–1964, and we believe that this is suggestive of manifestation of the cyclicity of atmospheric processes and is agreed with a gradual decrease in the rate of the temperature rise. In the last period duration of the period limiting human stay in the open air in the considered area remains high and ranges from 3.5 (to the west of 80° E) to 5 months on islands and capes of the region. So, as is demonstrated by the above example of space-time dynamics of the weather severity index at the time about 13 hours of local time, no decrease in the level of discomfort in polar Siberia is found.
Influence of the snow–soil contact conditions on the depth of ground freezing (based on observations in the Kursk region)
Authors: Kotlyakov V. M. , Sosnovsky A. V. , Chernov R. A.
Published: June 2019

The results of measurements of the ground freezing under a snow cover do not always agree with the calculations. The reason for this may be variability of thermal characteristics of the snow cover which properties depend on the landscape features. One of probable reasons may be also the incomplete contact between the snow cover and the soil. In autumn, the ground surface is usually covered with fallen leaves or withered grass. Estimates show that, in the presence of such layer on the soil surface, the air gap between snow and soil with the 1 cm thickness has a thermal protection capacity equal to the value of a 10‑centimeter thick layer of snow. Sometimes the presence of local gaps in the snow-soil interface can also be caused by other reason, for example, the spontaneous downfall of a depth hoar layer. The results of field measurements of snow cover characteristics, ground freezing depths and investigation of the contact conditions at the snow-soil interface carried out in different landscapes are presented. The results of mathematical modeling showed that when the air gap between snow and soil is taken into account the calculated values of depth of ground freezing are in a good agreement with data of the measurements. This consideration is especially important for small thicknesses of snow cover with high density and thermal conductivity. Numerical experiments did also show that the snow hardness is the necessary characteristic for analysis of the snow cover state. This provides more accurate estimating of the snow thermal conductivity that is closely connected with its hardness.
Influence of sea surface temperature in the tropics on the Antarctic sea ice under global warming
Authors: Alekseev G. V. , Glok N. I. , Vyasilova A. E. , Ivanov N. E. , Kharlanenkova N. E. , Smirnov A. V.
Published: June 2019

Sea ice fields in the Antarctic, in contrast to the Arctic ones, did not show a reduction in observed global warming, whereas the global climate models indicate its certain decrease. The purpose of the study is to explain this climatic phenomenon on the basis of the idea of joint dynamics of oceanic structures in the Southern Ocean – the Antarctic polar front and the margin of the maximum distribution of sea ice. We used data from the ERA/Interim and HadISST as well as the database on the sea ice for 1979–2017. Relationship between the SST-anomalies in low latitudes of the Northern hemisphere and positions of the Antarctic polar front and maximum sea-ice extent was investigated. It was found that locations of these structures changed under the influence of the SST anomalies in low latitudes. The results obtained confirm existence of the opposite trends in changes in the sea ice extent in the Arctic and Antarctic under the influence of the SST anomalies in the central North Atlantic Ocean. When positive, the anomalies cause a shift of the Intertropical Convergence Zone (ITCZ) and the Hadley circulation to the North, while, on the contrary, the negative anomaly promotes the corresponding shift of the Antarctic polar front, followed by the boundary of sea ice.
Diamonds in the Kamchatka Peninsula (Tolbachik and Avacha Volcanoes): Natural Origin or Contamination?
Authors: Pokhilenko N.P. , Shumilova T.G. , Afanas’ev V.P. , Litasov K.D.
Published: June 2019

—Lavas of the Kamchatka volcanoes store cubic-octahedral diamonds identical in morphology and structure to synthetic crystals, and their natural origin is doubted. Judging by published data, the diamonds discovered in the Tolbachik lavas are similar to synthetic diamonds made by different producers, and the analyzed samples rather result from contamination with synthetic material. Ophiolite-hosted diamonds reported from Europe, China, Mongolia, and Polar Urals look like the Tolbachik diamonds and are of the same type. The similarity between crystals coming from geologically dissimilar objects indicates that contamination may occur in those cases as well. Thus, diamonds found in unusual hosts or geologic settings require careful checking. These findings have to be reproduced repeatedly in other in situ samples and approved by independent experts; with all respect to the priority of the first finders, the sampling sites should be open to many researchers, especially the respective specialists. The inevitable disproval of false diamond findings is discouraging and discredits the true discoveries. Possible contamination with synthetic or natural material from cutting tools has to be excluded in all newly found diamonds before claiming their natural origin.
Geochemistry and Isotopic Age of Zircons from Rocks of Ultramafic Massifs in the Southern Folded Framing of the São Francisco Craton (Southeastern Brazil)
Authors: Lesnov F.P. , Pinheiro M.A.P. , Sergeev S.A. , Medvedev N.S.
Published: June 2019

—We present the first data on the geochemistry and isotopic age of zircons from rocks of the Roseta (lherzolite and olivine orthopyroxenite) and Córrego da Areia (olivine orthopyroxenite) ultramafic massifs localized among Archean–Proterozoic metamorphic strata in the southern folded framing of the São Francisco Craton. The examined zircons differ in crystal morphology, the intensity and type of cathodoluminescence, oscillatory zoning, the distribution of trace elements, and U–Pb isotopic age. Zircon crystals from the Roseta lherzolite have an age of 800-728 Ma and show negligible cathodoluminescence. Some of them have reaction rims with an age of 663–619 Ma. The crystal cores are enriched in rare earth elements (REE) but are often depleted in U as compared with the reaction rims. The age of zircons from the Roseta olivine orthopyroxenite showing moderate cathodoluminescence is within 622.6–596.9 Ma. Zircons from the Córrego da Areia olivine orthopyroxenite show moderate to intense cathodoluminescence and often have a rhythmic oscillatory zoning. They are characterized by an uneven distribution of REE and other trace elements and have high contents of U and Th. Most of these zircons have an ancient isotopic age (2558–2100 Ma). The examined zircons are of several types: relict, xenogenic, syngenetic, and epigenetic. The Roseta and Córrego da Areia massifs are considered to be protrusive outliers of a deep-seated Precambrian mafic–ultramafic complex, which were tectonically transferred along faults into the intensely metamorphosed Archean–Proterozoic strata in the southern folded framing of the São Francisco Craton.
The Sources of Paleoproterozoic Collisional Granitoids (Sharyzhalgai Uplift, Southwestern Siberian Craton): from Lithospheric Mantle to Upper Crust
Authors: Turkina O.M. , Kapitonov I.N.
Published: June 2019

—The paper presents the geochemical and isotope characteristics of rocks and the U–Pb age and Lu–Hf isotope composition of zircons from three plutons of Paleoproterozoic granitoids in the Sharyzhalgai uplift (southwestern Siberian craton). The age of granitoids of the Toisuk (1838 ± 6 and 1827 ± 9 Ma), Nizhnii Kitoi (1846 ± 7 Ma), and Malaya Belaya (1863 ± 16 Ma) plutons corresponds to the Late Paleoproterozoic collision stage and is correlated with the time of mafic magmatism. The studied rocks have a wide range of silica contents. The Toisuk pluton is composed of a range of rocks from monzodiorites to granodiorites (granosyenites) and granites; the Nizhnii Kitoi pluton, of granodiorites and granites; and the Malaya Belaya pluton, of leucogranites. The rocks of the three plutons are highly ferroan, enriched in LREE, Th, and HFSE, and correspond in composition to A-type granitoids. A characteristic feature of melanocratic granitoids of the Toisuk and Nizhnii Kitoi plutons is extremely high contents of Ba: 4080–1500 ppm and 1560–990 ppm, respectively. Based on analysis of experimental data on the melting of various substrates and the results of numerical simulation, it is assumed that monzodiorite–granodiorites of the Toisuk pluton and granodiorites of the Nizhnii Kitoi pluton resulted from the differentiation/melting of a mafic source similar in Ba and Sr contents to intraplate continental basalts. The isotope compositions of zircon and melanocratic granitoids of the Toisuk (εHf from –6.0 to –10.7 and εNd from –5.3 to –10.2) and Nizhnii Kitoi (εHf from –5.0 to –8.1 and εNd = –4.0 and –5.1) plutons argue for the generation of their mafic sources from the enriched lithospheric mantle formed as a result of Neoarchean subduction processes. Vein granites of the Toisuk pluton and leucogranites of the Malaya Belaya pluton formed through the melting of quartz–feldspar (granodiorite) substrate. The contrasting isotope parameters of the Toisuk vein granites (εHf from –6.7 to –10.1, zircons, and εNd = –5.5, rock) and Malaya Belaya leucogranites (εHf from 2.9 to 5.9, zircons, and εNd from +0.7 to –1.9, rocks) indicate melting of the Archean and Paleoproterozoic crust, respectively. The more radiogenic Hf isotope composition of zircons from vein granites as compared with rocks of the Archean crust of the Irkut terrane is evident of the contribution of juvenile material to the granite formation.
Effect of Transmitter Current Waveform on Transient Electromagnetic Responses
Authors: Antonov E.Yu. , Mogilatov V.S. , Epov M.I.
Published: June 2019

—The theoretical studies and methodological guidelines for transient electromagnetic (TEM) surveys assume an ideal step turn-off of transmitter current. Yet, the pulse duration in the survey practice is nonzero: It depends on penetration depth and has economic or logistic limitations. The turn-off time, which cannot be too short for technical reasons, affects especially the late-time transient responses, while the transmitter waveform is more essential at early times. Therefore, forward calculations of voltage decay should take into account the real parameters of the turn-off ramp. Earlier it was suggested to use transmitter current of a special waveform to improve the resolution of TEM soundings, e.g., in the designed and successfully tested compensation method. In this study the problem is treated from a broader perspective, in terms of TE and TM polarization of the TEM field. The two components are excited by different sources and behave in different ways in responses of a two-layer earth with a resistive lower layer to transmitter current of different waveforms.
Gold-Bearing Pyrrhotite Ores in East Sayan: Composition and Formation Conditions (by the Example of the Ol’ginskoe Ore Occurrence)
Authors: Damdinov B.B. , Damdinova L.B. , Zhmodik S.M. , Mironov A.G.
Published: June 2019

—We present results of study of the chemical composition, formation conditions, and genesis of gold-bearing pyrite–pyrrhotite ores widespread within the ophiolite belts in the southeast of East Sayan. The study was performed at the Ol’ginskoe ore occurrence localized in the Ol’gino gold ore zone. Sulfide mineralization zones are composed of lenticular interbeds and bodies subconfoimable with the bedding of the enclosing schist strata. The ores are carbonaceous siliceous garnet–biotite schists variably enriched in sulfide minerals, mainly pyrrhotite, with impurities of other silicate minerals: tremolite, chlorite, albite, plagioclase, diopside, and epidote. In addition, sphalerite, chalcopyrite, pyrite, and arsenopyrite are present in small amounts in the ores. The established Р–Т conditions of ore metamorphism (T = 430–540 °C, P ~ 5 kbar) correspond to the lower boundary of the epidote–amphibolite facies. Thermobarogeochemical studies of fluid inclusions in vein quartz showed close temperatures (536–340 °C) but lower pressures, 200–800 bars, which indicates that the quartz vein formation was related to a pressure drop. The predominant salts of the fluid inclusions are Fe and Mg chlorides with Na and K impurities. The geologic location, structures, textures, and mineral, geochemical, and isotope compositions of the studied sulfide ores indicate their formation in submarine deep-water environments as a result of the activity of hydrothermal systems, analogues of “black smokers”, later subjected to metamorphism. During metamorphism, primary ores underwent mineral and chemical transformations: pyrrhotitization of pyrite, appearance and coarsening of native gold particles, and redistribution of components (Mn, As, etc). The low contents of gold and some ore-forming elements (Zn, Cu, and Pb) in pyrrhotite ores testify to the removal of these elements with a metamorphogenic fluid. The removed ore-forming components might have been a source of material for later gold–sulfide–quartz deposits of the Urik–Kitoi zone in East Sayan.
Reconstruction of Magma Flow in Permo–Triassic Intrusions of the Angara–Taseeva Syneclise (Siberian Platform) Based on Magnetic Susceptibility Anisotropy Data
Authors: Latyshev A.V. , Ul’yakhina P.S. , Veselovskii R.V.
Published: June 2019

—Based on detailed studies of the anisotropy of magnetic susceptibility (AMS), the directions of magmatic-melt propagation have been reconstructed in large dolerite sills of the Angara–Taseeva syneclise. Half the sites studied showed a magnetic fabric of “normal” type, i.e., the minimum K3 axis of the AMS ellipsoid is orthogonal to the contact, and the other two axes lie in the plane of the intrusive body. Interpreting the orientation of the maximum K1 axis as the direction of the melt flow at such sites, we compiled a scheme of the main magma flow directions. The obtained results are generally consistent with the hypothesis of magma-feeding zone in the central, most downwarped part of the Angara–Taseeva depression. The distribution of the maximum axes of the AMS ellipsoid is different in sills and points to the existence of local intrusion centers. Intrusions with an AMS ellipsoid of “reverse” type are predominant on the periphery of the depression. The sites with a “normal” magnetic fabric do not demonstrate any prevailing direction of magma propagation, because there is no general direction of the melt flow in the peripheral subsurface zones of large intrusions.
A Model of Keyboard-Like Nonuniform Exhumation as a Possible Cause Zoning of Metallogenic Belts in Folded Areas (Eastern Transbaikalia and Southern Primorye)
Authors: Kigai I.N.
Published: June 2019

—Zoning of metallogenic belts is observed in folded areas of all metallogenic epochs from Precambrian to Cenozoic. The changes observed across the strike of folded areas on geological mapping are usually treated as geodynamic, petrometallogenic, or temporal specialization of corresponding belts (terranes) and zones. However, there are serious petrological reasons to expect a significant downward change in the basicity of magmatites and the composition of related mineralization in folded areas. The change may be caused both by relationships between the densities of magmas and country rocks and by relationships between the solidus temperatures of different magmas and the thermal gradient pattern on the magma ascent path. More basic magmatites and related mineralization should be detained at the deeper levels of the lithosphere because of the higher density and higher solidus temperature of magmas. During orogeny, the vertical differential movements of several adjacent terranes located between deep-seated faults can create keyboard-like structures composed of parallel belts variously uplifted and subsided, similarly to white and black keys of a piano. In belts and blocks of such structures more uplifted and then more subjected to denudation, the ore-magmatic complexes earlier located at deeper levels can expose at the surface. As a result, zoning of metallogenic belts can form, which is totally or only partly related to the metallogenic specialization of structure-facies zones and terranes. The possibility of this origin of zoning of metallogenic belts is shown with the use of geophysical data for two important ore-producing regions of Russia — eastern Transbaikalia and southeastern Primorye. The above model is proposed as one of the possible ways of metallogenic-belt formation in some other folded areas.

The author hopes that this work will stimulate a more profound analysis of the nature of metallogenic-belt zoning in the considered and other world regions with the use of modern geophysical methods. The use of the described regularities of the storied arrangement of magmatites of different basicity and oxidation states and genetically related hydrothermal ores may facilitate prospecting for ores of different metals and their 3D forecasting in keyboard-like structures of Phanerozoic orogens and ancient platforms.
Silurian Terrigenous-Carbonate Sedimentaion in Gorny Altai: Structure, Facies Variability, Faunal Assemblages, and Stratigraphic Position
Authors: Sennikov N.V. , Khabibulina R.A. , Obut O.T. , Novozhilova N.V. , Tokarev D.A. , Luchinina V.A.
Published: June 2019

—This paper discusses the structure and facies variability of the Silurian mixed terrigenous-carbonate strata and presents new paleontological and biostratigraphic data. It attempts to refine the stratigraphic position and provide new lithologic evidence (markers) for regional manifestations of global sedimentary events (Mulde transgressive-regressive and Linde regressive events) in the Altai sections. The chronostratigraphic position of the Kuimov Horizon, a regional stratigraphic unit, has been defined based on graptolite and conodont faunas.
Mantle–Crustal Nature of Early Paleozoic Alkaline Intrusions in Central Sangilen, Tuva (from Nd, Sr, Pb, C, and O Isotope Data)
Authors: Vrublevskii V.V. , Nikiforov A.V. , Sugorakova A.M. , Kozulina T.V.
Published: June 2019

—The Paleozoic foidolite–foyaite plutons of the Sangilen upland (Bayan-Kol, Dakhu-Nur, Chik, and Kharly ones) might have formed in the Late Cambrian–Early Ordovician (~490–500 Ma, Sm–Nd and U–Pb); they are the result of the oldest alkaline magmatism in southeastern Tuva. The intrusion was accompanied by the formation of high-temperature (up to ~600–900 ºC) endogenous carbonate rocks containing calcite, alkali pyroxene, Na–Ca amphibole, biotite, fluorapatite, microcline, and nepheline. Silicate and carbonate derivates were produced, most likely, from genetically related heterogeneous sources with εNd(T) varying from 3.0 to 6.3 and from –0.5 to 6.5, respectively, which might be due to the mixing of the depleted (PREMA) and enriched (EM) mantle materials. Initial ratios 207Pb/206Pb ≈ 0.89 and 208Pb/206Pb ≈ 2.15 in K-feldspar from calcitic rocks are close to those of EM 1. The correlation between the stable-isotope ratios (δ18O ~ 7.2–19.5, δ13C from –6.0 to –1.4‰) and the high 87Sr/86Sr(T) ratio (0.7057–0.7076) indicates a significant crustal contamination of magma in the upper horizons of the lithosphere and a minor impact of a meteoric fluid. The assumed synchronous formation of the studied plutons and other alkaline rock complexes of the Early Paleozoic Large Igneous Province in the west of the Central Asian Orogenic Belt as well as their isotope similarity do not rule out that the intrusion took place in the plume–lithosphere interaction setting.
Seismic Activity of the Khambinskii Fault (Southwestern Transbaikalia)
Authors: Smekalin O.P. , Chipizubov A.V. , Radziminovich N.A. , Imaev V.S.
Published: June 2019

—The paper presents results of a seismogeological study based on analysis of seismic data and historical facts about the seismic activity of the Khambinskii fault zone. According to the data obtained, a genetic type of dislocations on conjugate faults (Gusinoe Ozero and Orongoi paleoseismogenic structures) is related to reverse faults with a strike-slip component. Geophysical studies of the Gusinoe Ozero structure have determined the dip of the fault plane toward the mountain framing of the depression and its outcrop at the bottom of the seismic scarp. The significant seismic potential of the Khambinskii fault is responsible for the maximum intensity of shocks in the nearby cities and settlements of southeastern Transbaikalia. The seismic fault activity has been confirmed by the historical earthquakes of 1856 and 1885, the M = 5 earthquake that occurred on 2 October 1980, and at least two prehistoric earthquakes. The latest of the latter occurred no earlier than ~4 ka and had M = 7.0–7.3, while the earliest was even more intense and took place in the first half of the Holocene, no later than ~6 ka.
Composition and Genesis of Accessory Mineralization in Manganese Silicate Rocks of the Triassic Sikhote-Alin Chert Formation
Authors: Kazachenko V.T. , Perevoznikova E.V.
Published: June 2019

—Manganese silicate rocks together with silicate–magnetite ores and jaspers (Late Anisian–Ladinian) form lenticular or tabular bodies in the Triassic Sikhote-Alin chert formation. The lower part of the formation (Olenekian–Early Anisian) is enriched in clayey and organic matter. Nickel and cobalt compounds and other ore minerals in the Sikhote-Alin manganese silicate rocks belong to two genetic groups including minerals of the valence and ultimately reduced Ni, Co, and other metals. Minerals of the valence species of Ni, Co (sulfoantimonides, sulfoarsenides, sulfides, antimonides, arsenides, tellurides, and silicates), and other metals (galena, sphalerite, chalcopyrite, arsenopyrite, wolframite, scheelite, molybdenite, cassiterite, stannite, cinnabar, stibnite, boulangerite, jamesonite, bournonite, löllengite, bismuthite, fahlore, altaite, native Sb and Bi, etc.) formed from the protolith material during metamorphism under the same conditions as the rock-forming minerals. The presence of minerals of ultimately reduced Ni, Co (maucherite, native Ni, Ni phosphide, Ni and Co chromides, disordered solid solutions, and intermetallic compounds of Ni with Cu, Zn, Sn, and Pb), and other metals (native Pb, Zn, Fe, Sn, Se, Au, Pt, “cupriferous gold”, and intermetallic compounds of Cu, Sn, Pb, Sb, Al, and Zn) in the manganese silicate rocks is due to the influence of the organic matter of the underlying carbonaceous silicites. During metamorphism, the most volatile components (first of all, poorly bound water and hydrocarbons) were released from the heated carbonaceous rocks; as a result, a metal-enriched fluid with highly or ultrahighly reducing properties appeared, which migrated along fractures into other rocks. The manganese silicate rocks are the products of contact metamorphism of siliceous rhodochrosite rocks formed through the diagenesis of biogenic siliceous muds enriched in Mn oxides and organic matter. Erosion of the weathering crust of islands composed of gabbroids of the Kalinovka, Vladimiro-Aleksandrovskoe, and Sergeevka complexes (in the late Middle Triassic–Late Triassic) played the leading role in the formation of metalliferous sediments. Manganese silicate rocks localized in the stratigraphic column above the carbonaceous silicites of the Triassic chert formation are enriched in Au (up to 35.38 ppm), Pt (11.27 ppm), and Pd (5.33 ppm). They contain noble-metal minerals and a wide spectrum of native elements and intermetallic compounds. The presence of Au–Pd–Pt–Ni–Co association (typomorphic for basic and ultrabasic rocks) in the Triassic protoliths of the manganese silicate rocks and carbonaceous silicites is probably due to the sorption of these elements by Mn and Fe hydroxides and organic matter during the exogenous weathering of the ancient Sikhote-Alin gabbroids.
Lateral Zoning of Groundwater Chemistry and Authigenic Mineralogy in the Oxfordian Regional Reservoir of the Nadym–Taz Interfluve
Authors: Novikov D.A. , Vakulenko L.G. , Yan P.A.
Published: June 2019

—This is a pioneering study on lateral zoning of groundwater chemistry and authigenic mineralogy in the Oxfordian regional reservoir of the Nadym–Taz interfluve. According to thermodynamic calculations, the nonequilibrium–equilibrium water–rock system lacks equilibrium with primary magmatic minerals, such as albite, anorthite, and microcline, though the water is moderately saline (up to 63.3 g/L) and has been in interaction with rocks for ~165 million years. Authigenic minerals form continuously and successively (kaolinite–montmorillonite–illite–micas–chlorite–albite–microcline) from waters that have certain рH and contents of SiO2, Al, Na, K, Ca, and Mg. The equilibrium of groundwater with primary aluminosilicate minerals impinges on a carbonate barrier, and almost all rocks are more or less strongly carbonatized. Authigenic mineral assemblages from the southern Nadym–Taz interfluve include kaolinite unlike those from the northern part of the region, where albitization is more common. Authigenesis generally decays in the eastern direction.
Zirconology of the Lherzolite Block of the Nurali Massif (South Urals)
Authors: Krasnobaev A.A. , Rusin A.I. , Valizer P.M. , Likhanov I.I.
Published: June 2019

—Data on the mineralogy, geochemistry, and geochronology of zircons from plagioclase and spinel lherzolite and dunites of the Nurali massif are presented. The age of the main-type zircons from lherzolites (plagioclase ones, 446.2 ± 2.8 Ma, and spinel ones 433.3 ± 3.4 Ma) and dunites (443.8 ± 6.9 Ma) suggests their synchronous crystallization (Tav = 440 ± 5 Ma). The metamorphic age of zircons is 410–415 Ma. In addition to grains belonging to the main subset, the older grains with an age between 527 and 2045 Ma and newly formed metasomatic grains with an age of 380–385 Ma were found. The structure and REE patterns of most zircons from ultramafic rocks point to their magmatic origin, which is probably related to crystallization of a fluidized mantle melt.
Geochemistry of Soda Waters of the Chulym–Yenisei Artesian Basin (West Siberia)
Authors: Lepokurova O.E. , Shvartsev S.L.
Published: June 2019

—Results of studies of soda waters of the Chulym–Yenisei artesian basin are presented. It is shown that these waters are ubiquitous within Cretaceous or Jurassic sediments at depths of ~100–300 m to 1.5–2.3 km. According to the formation conditions, mineralization, and pH, they are divided into three groups: Type I waters spread to a depth of 600 m and have pH = 7.4–8.4 and TDS ≤ 0.5 g/L, type II waters occur at depths of 0.6–2.3 km and are characterized by pH = 8.0–8.9 and TDS = 0.7–4.1 g/L, and type III waters (“Omega”) form a local segment among type II waters and have a unique composition: high alkalinity (pH = 9.0–10.3) and low mineralization (TDS = 0.2–0.6 g/L). We focus special attention on type III waters and present results of studies of their microcomponent, gas, and isotope compositions. The cause of their low salinity and high pH is explained for the first time. Taking into account the isotope data (δD, δ18O, and δ13C), we have established the infiltration origin of soda waters of the three types and the biogenic source of their carbon dioxide. Calculations of equilibria in the water–host-mineral system have shown that all soda waters are in disequilibrium with many primary aluminosilicate minerals but are in equilibrium with a wide range of carbonates and clays. In passing from type I to type III waters, the number of minerals in equilibrium with water continuously increases (albite, microcline, muscovite, and biotite). Taking into account the data obtained, we present schemes of formation of different types of soda waters in the studied basin at different stages of the evolution of the water–rock– gas–organic-matter system and estimate the time of each stage.
The Late Cretaceous East Sikhote-Alin Volcanic Belt: Transition from Subduction to Sliding of Lithospheric Plates (Structure-Geological, Petrological, and Isotope-Geochemical Aspects)
Authors: Martynov A.Yu. , Golozubov V.V. , Martynov Yu.A. , Kasatkin S.A.
Published: June 2019

—The East Sikhote-Alin volcanic belt extending for ~1500 km is commonly considered a single tectonomagmatic structure formed during the Late Cretaceous subduction and the Cenozoic oceanic-slab breakup and active asthenospheric diapirism under transform plate sliding. Based on analysis of the published geological information and the new data on the age and trace-element and isotope compositions of the igneous rocks of the Late Cretaceous Bol’ba Formation, it is shown that the initial stages of volcanism in the southern and northern Sikhote-Alin took place in different geodynamic settings. In contrast to the coeval suprasubductional volcanics of the southern sector (Primorye), the volcanic section of the Bol’ba Formation is dominated by magnesian (Mg# = 26–40) adakites (La/Yb = 19–34) and high-Nb basalts. This igneous rock association and the lead (Δ8/4Рb = 30–46) and neodymium (0.51279–0.51281) isotope ratios of the studied rocks suggest the influence of the “hot” oceanic asthenosphere on magma genesis. The earlier slab breakup north of 48–49 °N was due to the oblique convergence of oceanic and continental lithospheric plates in the Late Cretaceous, accompanied by sinistral shears. The results obtained indicate that the lateral zonation of the eastern Sikhote-Alin is due to different geodynamic settings of formation of its northern and southern sectors rather than variations in its basement composition. In theoretical aspect, the performed research is important for the correct reconstruction of the geologic events in zones of convergence of oceanic and continental plates. It is necessary to take into account not only the general direction of the convergence but also the configuration of the plate boundary.
Early Paleozoic Granitoid Magmatism in the East Tannu-Ola Sector of the Tuvinian Magmatic Belt: Geodynamic Setting, Age, and Metallogeny
Authors: Vetrov E.V. , Chernykh A.I. , Babin G.A.
Published: June 2019

—The East Tannu-Ola sector of the Tuvinian magmatic belt is composed of Early Cambrian volcanosedimentary rocks of an island-arc association (Kadvoi, Serlig, and Irbitei Formations), which are intruded by granitoid massifs of different ages (from Cambrian to Devonian) of the Tannu-Ola areal pluton. We analyzed the structural and geologic position, chemical composition, metallogenic signatures, and geochronological (U/Pb) and isotope-geochemical (Sm/Nd and Rb/Sr) characteristics of Early Paleozoic granitoids of the Ungesh pluton (western part of the Tannu-Ola areal pluton). The available and our new data made it possible to establish the specific chemical parameters, age sequence, duration, intensity, and metallogeny of granitoid magmatism in the East Tannu-Ola sector of the Tuvinian magmatic belt. An early Cambrian (534–518 Ma) gabbro–plagiogranite complex similar to the Maina complex in West Sayan has been recognized in the Ungesh pluton. The age and metallogeny of the middle–late Cambrian (508–492 Ma) Tannu-Ola diorite–granodiorite–plagiogranite and Late Ordovician (451–447 Ma) Argolik granite–leucogranite complexes have been refined. Granitoids of the early Cambrian complex formed probably at the initial stage of formation of an island arc, in association with the Kadvoi–Serlig basalt–andesite–rhyolite complex. It is in these granitoids that early low-productivity gold–sulfide–quartz veins and veinlets originated. Granitoids of the Tannu-Ola complex formed at the initial stage of evolution of the accretion–collision system. Magnetite-containing skarns and numerous vein–veinlet zones of late high-productivity gold-sulfide-quartz mineralization evolved in these granitoids. Granitoid massifs of the Argolik complex formed at the final stage of evolution of the accretion–collision system and probably played a crucial role in the regeneration of ore mineralization in some areas.
Tectonophysical Paleostress Reconstructions: Interpretation Challenges and Possible Solutions
Authors: Rebetsky Yu.L. , Marinin A.V. , Sim L.A.
Published: June 2019

—Paleostress inversion may be ambiguous when several markedly different local stress states are inferred for a group of outcrops. Attempts of reconstructing regional stress regimes (compressional, extensional, or strike-slip) by selecting local principal stresses of proximal directions turn out to have poor grounds. Each stress permutation (e.g., extension to compression) attendant with buildup of large irreversible strain (fault slip) requires a 5–6 kbar change in middle-crust horizontal stress and at least 50 Myr stable and uniform loading. Tectonophysical stress reconstructions for present active intracontinental orogens show heterogeneous patterns: Stress directions in uplifts are different from those in large intermontane basins and even in relatively subsided parts of mountain ranges or in adjacent uplifted zones (e.g., a plateau and a range). Paleostresses should be interpreted with reference to present stress fields in the respective areas. It is suggested to reconstruct regional stresses using the approach of L. Sim implying search for “common stress fields”. Another important technique is to trace stress changes in specific structures (large folds etc.) in the course of their evolution. The available data indicate correlation and bipolarity of stress states in large basins and uplifts.
Behavior of Noble Metals during Fractional Crystallization of Cu–Fe–Ni–(Pt, Pd, Rh, Ir, Ru, Ag, Au, Te) Sulfide Melts
Authors: Sinyakova E.F. , Kosyakov V.I. , Borisenko A.S. , Karmanov N.S.
Published: June 2019

—The method of quasi-equilibrium directional crystallization was used for experimental modeling of the behavior of noble metals in the presence of Te during the fractional crystallization of Cu- and Ni-rich sulfide magma. The experimental melt contained (mol.%): Fe = 18.5, Ni = 19.1, Cu = 16.7, S = 44.1, and Pt = Pd = Rh = Ir = Ru = Ag = Au = Te = 0.2, i.e., is similar in composition to the massive pentlandite-bornite ores of platinum-copper-nickel deposits of the Noril’sk group. The crystallized sample consists of six primary zones differing in chemical and phase compositions. The main minerals crystallizing from the melt include the following sulfide phases: bornite solid solution (bnss), quaternary solid solution (tss), described earlier in the literature, and three phases (сfpn, cnpn, npn), which we attributed to pentlandite according to their chemical composition. The primary phases crystallized from the melt decay on cooling with the formation of secondary phases. The сfpn, cnpn, and tss phases decay completely, and the npn and bnss phases, partly. As a result, secondary zoning forms in the sample. Formation of drop-like inclusions of telluride melt was observed in the end zone of the ingot. The obtained data show that pentlandites and tss are the main high-temperature concentrators of PGE, with each of the macrophases showing specific PGE accumulation. Eight types of impurity phases have been detected. They form by different mechanisms: crystallization from sulfide melt of refractory compounds, deposition from telluride melt, and formation through complete or partial decay of primary macro- and microphases. A scheme of the zonal structure of the crystallized sample and the evolution of the phase composition during fractional crystallization has been constructed. It clearly demonstrates the intricate formation of primary and secondary major-component and impurity zonings and can be used to explain the nature of the zoned structure of massive PGE-bearing pentlandite–bornite orebodies.
New Data on Granitoids of the Kara Gold Ore Cluster (Eastern Transbaikalia): Age, Genesis, and Sources of Material
Authors: Efremov S.V. , Spiridonov A.M. , Travin A.V.
Published: June 2019

—Study of granitoids spatially and genetically associated with gold mineralization within the Kara gold ore cluster has provided a new insight into their genesis, association with ore mineralization, and the sources of their ore material. The regional granitoids associated with gold mineralization are part of two individual complexes. One of them, earlier assigned to the Amanan complex, has an isotopic age of 182.9 ± 2.6 Ma and must be related to the subduction zone that existed on the southern margin of the Siberian continent in that period. Its granitoids differ in age and composition from the granitoids of the Amanan complex and must be separated as an independent taxonomic unit after an additional geological study. The second, Amudzhikan–Sretensk, complex has an isotopic age of 151.7 ± 1.9 Ma and might be related to the collision of the Siberian and Mongol–Chinese continents after the closure of the Mongol–Okhotsk ocean. In geochemistry the granitoids of the Amanan(?) complex correspond to adakites and must be considered melting products of the basaltic layer of the oceanic lithosphere. The granitoids of the Amudzhikan-Sretensk complex are similar in geochemistry to sanukitoids, melting products of subcontinental sources contaminated with continental-crust material. The granitoids of both complexes have high contents of gold and must be considered gold-bearing. In the Amanan(?) complex, adakites are the gold-richest rocks (as estimated from the slab melt composition), which indicates the primary nature of this gold. In the Amudzhikan–Sretensk complex, the highest contents of gold are specific to primitive sanukitoids, melting products of a mantle source with gold signatures. This suggests the primary nature of gold, whose content is determined by the portion of slab melt in the source of the rock material. The presence of adakites and primitive sanukitoids in the regional granitoid complexes indicates the existence of a subcontinental mantle source with gold signatures during the magma generation. The source formed in the subduction zone that existed on the southern margin of the Siberian continent in the Early Jurassic and was remobilized under collision of the Siberian and Mongol–Chinese continents in the Late Jurassic. This source might have controlled both granitoid magmatism and ore mineralization.
Tectonic Evolution of Late Mesozoic–Cenozoic Basins in Eastern China and Implications for Pacific Plate Subduction
Authors: Wang Hongliang , Liang Jintong
Published: June 2019

—During the late Mesozoic and Cenozoic, the North China Craton witnessed a series of tectonic transition and deformation events, caused mainly by the subducting Pacific Plate and forming many petroliferous basins in eastern China and adjacent areas. Based on analysis related to the reconstruction of balanced sections, the comparison of subsidence rates, and the migration of depocenters in these basins, the tectonic evolution of these basins and their relationships with each other are clearly revealed. The evolution of the Bohai Bay Basin shows a migration from southwest to northeast. The North Yellow Sea Basin’s evolution developed northward, while the South Yellow Sea Basin evolution migrated southwards. The evolution of the East China Sea Basin was activated from northwest to southeast. In combination with the subduction of the Pacific Plate, the conclusions of this study can be summarized in three aspects: (1) The structural pattern of the basin group is characterized by east–west trending belts and north–south trending blocks, (2) tectonic activities in the late Mesozoic–Cenozoic basins evolved from west to east in response to the westward subduction of the Pacific Plate, and (3) due to the collision of the Eurasian Plate and Indian Plate and the transitional pattern of the Tan-Lu Fault Zone from sinistral to dextral, the tectonic evolution of the basin group was centered in the Yellow Sea Basin with the Bohai Bay Basin, evolution migrating northward and the ECSB migrating southward.
Seismogeological Criteria for the Gas Potential of Aptian–Cenomanian Sediments in the North of West Siberia (by the Example of the Yubileinoe Field)
Authors: Kontorovich V.A. , Surikova E.S. , Ayunova D.V.
Published: June 2019

—Seismogeological criteria for the gas potential of the Aptian–Cenomanian sediments of West Siberia are substantiated. The research was carried out by the method of integrated interpretation of seismic materials, well logs, well test results, and petrophysical studies. As a reference object we used the Yubileinoe oil and gas condensate field located in the Nadym–Pur interfluve, in which a unique gas deposit is concentrated in the Cenomanian reservoir PK1 and the Albian sand bed PK18. Based on the research results, seismogeologic criteria for gas prediction have been formulated. Massive Cenomanian gas pools are displayed in wave seismic fields by: (1) the presence of reflectors formed at the gas–water contacts in time sections and a decrease in the amplitude parameters of the reflector G confined to the roof of Cenomanian sequence; (2) an increase in the time thickness (ΔT), a decrease in the interval velocities (Vint), and a decrease in the amplitude–energy parameters of the seismic record in the Aptian–Cenomanian sequence. Aptian–Albian sheet gas pools are displayed in the wave fields by a sharp increase in the amplitudes of the seismic record, forming “bright spot” anomalies in the time sections.