The article presents the results of an analysis of data obtained on the Yamm–Torzhok regional profile, which crosses the Ilmen anomaly of electrical conductivity along its main axis. These works continue the long-term study of the structure of the Precambrian basement complexes of the western part of the East European Platform by the staff of the Department of Geophysics of the Faculty of Geology of Moscow State University and GEMRC IPE RAS. Based on the obtained data, together with the analysis of potential fields, a deep geoelectric model was constructed, and a model of the sedimentary cover structure was presented separately.
Kuzmin I.A, Tolstykh N.D.
Sobolev Institute of Geology and Mineralogy of the Siberian Branch of the RAS, Novosibirsk, Russia;
Keywords: Talnakh intrusion, main layered series, picritic gabbro-dolerites, inverse zoning, hybrid magma.
Norilsk-type intrusions are characterized by unique reserves, disseminated copper-nickel mineralization, which is localized in picrite and taxitic gabbro-dolerites. At the same time, if picrite and taxitic gabbro-dolerites are usually genetically separated from each other, then the mechanism of formation of picrite gabbro-dolerites themselves is still under discussion. Most often, they are considered as a cumulative part of a layered series. The work shows a sharp geochemical contact between the layered series and picrite gabbro-dolerites, in the section of which, in turn, we have identified an inverse geochemical zoning, expressed in the patterns of accumulation of petrogenic elements that do not fit into a single trend of crystallization differentiation with the rocks of the main layered series. The discreteness of rocks within the horizon of picritic gabbro-dolerites is demonstrated - two intervals are distinguished: the lower one with low chromium concentrations, with stable europium and strontium anomalies, and the upper one, which is characterized by abnormally elevated Cr2O3 contents, reduced LILE concentrations and the absence of a pronounced europium maximum, typical of the lower part of picritic gabbro-dolerites. Based on the known models of formation of inverse zonality of marginal zones of layered massifs, the article presents a new genetic scheme for the formation of picritic gabbro-dolerites as products of pulsation intrusion, which suggests that the lower part of picritic gabbro-dolerites was formed from hybrid magma, and the upper one - from primitive magma, due to pulsation filling of the formation chamber, which, in our opinion, is associated with inverse zonality and accumulation of chromium in the upper part of picritic gabbro-dolerites.
V.V. Lapkovsky, M.V. Lebedev, E.A. Ianevits 1Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia
2OOO Tyumen Petroleum Research Center, Tyumen, Russia
3Branch of Lukoil-Engineering LLC "KogalymNIPIneft",Tyumen, Russia
Keywords: Stochastic modeling of structural uncertainties; probabilistic estimation of resources; estimation of seismic velocity anomalies, probability distribution of structural trap areas, lognormal distribution of structural trap areas
In the new paradigm of the Russian oil and gas industry, much attention is paid to small hydrocarbon fields. This statement increases the requirements for the accuracy of forecasts of total hydrocarbon reserves in small-scale anticlinal traps. Such forecasts can be made by probabilistic estimation of resources, taking into account the probabilities of the field existence. The objective of the present research is the development of the scientific approach to quantifying the uncertainties associated with the existence and geometric parameters of small-scale anticlinal hydrocarbon traps mapped by modern 3D seismic exploration. The main method of solving this problem is stochastic modeling of structural uncertainties based on errors of structural mapping. The results of the study are summarized as follows. The type and parameters of the probability functions of the structural area are determined by the intensity and size of the velocity anomalies, as well as the parameters of the trap itself and the nature of its structural environment. The distributions of the structural closure areas can be described by functions in which the Mean value is greater than the quantile P50 value, the Mean value is approximately equal to the P50 value, and the Mean value is less than the P50 value. The lognormal distribution, which is commonly used to model structural uncertainty, is just one of the possible options. For small-scale hydrocarbon traps, their amplitude is comparable to the thickness of a productive reservoir; therefore, a change in the amplitude of the trap determines a change in the weighted average oil-gas-saturated thickness. As a result of the modeling, a positive relationship was established between variations in the anticline traps areas and their amplitudes. Accordingly, this relationship must be taken into account during the probabilistic assessment of the resources of this kind of the hydrocarbon traps. Otherwise, there may be a significant reduction in the range of uncertainty in resource estimates. Stochastic modeling of structural uncertainties is also a method of estimating the probability of the existence of anticlinal traps mapped by seismic exploration.
A.A. Tsygankov, G.N. Burmakina
Dobretsov Geological Institute of Siberian Branch of Russian Academy of Sciences, Ulan-Ude, Russia
Keywords: Angara-Vtitm batholith, U-Pb isotopic age, Lu-Hf, sources of magma sources, geodynamics, Western Transbaikalia.
The Late Paleozoic granitoid province of Transbaikalia (Angara-Vitim batholith, AVB, Russia), located in the northeastern part of the Central Asian Orogenic Belt (CAOB), covers an area of about 200,000 km2 and is composed of rocks ranging in composition from monzonites and quartz syenites to leucocratic granites. This work is aimed at: 1) determination of the total duration and dynamics of the formation of granitoids of the Angara-Vitim batholith; 2) finding the causes that determined the spatial and temporal heterogeneity of granitoids; 3) reconstruction of the sources of salic (granitoid) magmas, assessment of the contribution of mantle-crustal interaction processes to the petrogenesis of granitoids. The article is based on new petro-geochemical, isotopic (Lu-Hf) and isotopic-geochronological (U-Pb) data on the northern part of the AVB. Combined with the results of previous studies, it has been established that one of the largest granitoid provinces on Earth (AVB) was formed ~ 45 million years ago (from 320 to 275 million years). About 90% of the batholith rocks were formed during this time. Mainly crustal metagravaccian protoliths were the source of salic magmas. Formation of monzonitoids, quartz syenites, and granodiorites is associated with melting of mixed protoliths, in which the proportion of juvenile mafic material could reach 40-50%. The Late Paleozoic granitoid magmatism of Transbaikalia began with the actual introduction of calcareous-alkaline granites, granodiorites, and quartz syenites, which make up the bulk of the first stage of magmatism. At the second stage, magmatism was concentrated in a relatively narrow (200-250 km) permeable zone of the northeastern strike. This zone drained crustal foci of salic magmas and favored the entry of mafic mantle melts into the upper horizons of the Earth's crust. The granitoids of the Angara-Vitim batholith were formed at the post-collisional stage of the evolution of the eastern segment of the CAOB under the influence of mantle plume on the crust of the young orogen.
D.V. Metelkin1,2, E.V. Vinogradov1,2, A.A. Eliseev1,2, M.E. Luzan1,2, V.V. Abashev3 1Novosibirsk State University, Novosibirsk, Russia 2Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia 3Geological Institute Russian Academy of Sciences, Moscow, Russia
Keywords: Hotspots, mantle plumes, geodynamo, geomagnetic reversal frequency, paleointensity, geocentric axial dipole, equatorial dipole, anomalous geomagnetic field, global magnetic anomalies, absolute plate reconstructions
We present an analysis of modern paleomagnetic data from large igneous provinces and palaeorift structures in Siberia and the High Arctic that are potentially related to mantle plumes. The interrelationship between plume magmatism, geomagnetic reversal frequency, and field intensity over the last 600 Myr exhibits a periodicity of 70–100 Myr. Periods of mantle plume activity were preceded by an increase in geomagnetic reversal frequency, accompanied by a decrease in geomagnetic field intensity. Our proposed hypothesis explains this effect by changes in the thermal convection in the Earth’s outer core while mantle plumes are regarded as regulators of the state of the hydromagnetic dynamo. “Overheating” of the core increased the turbulence of convective currents, and therefore, the amount of reversals. During reversals, the value of the main component of the geomagnetic field – the geocentric axial dipole – first fell to zero and returned to high values only afer a full reversal of the poles. Reduction of relaxation time in periods of frequent reversals led to prolonged low values of the absolute intensity of the geomagnetic field. Mantle plumes forming during such periods could remove the excess heat and stabilize the state of the geodynamo, even almost completely stopping reversals. We link the Vendian and Devonian geomagnetic phenomena to periods of ultra-frequent reversals. During these extended periods of low value of the axial dipole, the configuration of the geomagnetic field was determined by low-order non-zonal harmonics and by the global magnetic anomalies. We observe a qualitative coincidence of the position of paleopoles with centers of lower mantle gravitational and magnetic anomalies and postulate that the anomalies were stationary. This is the basis for substantiating a new reference framework for paleotectonic reconstructions in absolute coordinates. Examples of reconstructions made using this system also agree with the hypothesis of stationary hotspots. From the terminal Precambrian to the Mesozoic inclusively, the Siberian paleocontinent was located in the area of effect of the African mantle hot field, migrating northwards along the 0° meridian from the latitude of Tristan da Cunha to that of Iceland.
V.S. Shatsky1,2,3, A.L. Ragozin1, V.N. Reutsky1, V.V. Kalinina1 1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Science, Novosibirsk, Russia 2 Novosibirsk State University, Novosibirsk, Russia 3 A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: inclusions in diamonds, diamond formation, mantle, subduction zone
Evidence of the involvement of Fe-C-O melts in diamond formation from placers in the northeastern Siberian Craton, along with our previously obtained data on iron carbide inclusions and literature sources, has provided a new perspective on processes diamond formation in subduction zones. Iron carbide and oxide inclusions in diamonds, along with the presence of moissanite and carbonates in polyphase inclusions, indicate a heterogeneous diamond environment. Extreme variations in oxygen fugacity during diamond formation processes can be caused by the generation of hydrogen and hydrocarbons during the interaction of carbonated rocks of the subducting oceanic lithospheric plate with aqueous fluids. Separated hydrocarbon fluids can create local areas of ultra-reduced mantle, where silicon carbide can be formed under conditions of the absence of equilibrium with the surrounding rocks.. A characteristic feature of the diamonds studied is that they were subjected to brittle deformation, followed by crack healing, accompanied by the formation of polyphase inclusions of iron carbides and oxides, which we interpret as melt inclusions. Brittle deformations of diamonds, in the conditions of the lower lithosphere, are explained by high deformation rates, which can be realized in the hypocenters of deep-focus earthquakes of the subducting lithospheric plate, during dehydration processes or the formation of carbonatite melts.
A.N. Didenko1,2, M.Y. Nosyrev2, G.Z. Gilmanova2, M.D. Khutorskoy1 1Geological Institute of the Russian Academy of Sciences Moscow, Russia 2Institute of Tectonics and Geophysics FEB RAS Khabarovsk, Russia
Keywords: Amur Plate, Curie Point Depth, plate boundaries, thermal anomalies and tectonic structures
Based on the results of spectral analysis of the anomalous magnetic field, the depths of the roof and the sole of the magnetically active layer of the Amur Plate and adjacent territories are calculated. The causes of variations in the depth of the sole of the magnetoactive layer (CPD) from 14 to 38 km (average 24 km) have been determined. Maximum CPD depths are observed within sedimentary basins (Erlian, Songliao, Sredneamursky) in the southwest and in the central part of the plate. The areas of minimum depths in the continental part are located in the northwest within the giant granitoid batholiths (Angara-Vitim, Khentei) and in the northeast within the Bureinsky province. The third area of minimum CPD values is located within the waters of the Sea of Japan.
The relatively high elevation of the bottom of the magnetically active layer in the Sea of Japan is associated with rifting processes in the back-arc basin, which began at the end of the Oligocene, and the generation of fluids and magma chambers above the Pacific slab, sinking under the Amur Plate. Two areas of high CPD standing in the continental part of the plate are associated with the presence of two thermal anomalies. The north-western one is explained by the presence of a thermal crustal anomaly due to the process of radioactive heat generation by granitoids of the giant Angara-Vitim, Khangai and Khentei batholiths. Northeastern Bureinskaya – the presence of an anomalous temperature of the mantle here.
A comparison of the newly constructed CPD map with the boundaries of the Amur Plate, previously determined mainly from seismic data, shows that the surface boundaries of the plate coincide mainly with the zones of the greatest CPD gradients. All of them are associated with areas of increased seismic energy generation, with the exception of one small area on the southern border of the Amur Plate at its junction with the Yangtze Plate. In our interpretation, plate boundaries are not just lines on the surface, they are fairly wide zones from tens to the first hundreds of kilometers that encircle the plate.
I.S. Sotnich1, E.A. Kostyreva1 1Trofimuk Institute of Petroleum Geology and Geophysics of Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia
Keywords: organic matter, bitumoids, hydrocarbon biomarkers, pyrolysis, catagenesis, maturity, Bazhenov Formation, Western Siberia.
The article presents the results of detailed organic geochemistry studies being part of a comprehensive (lithological, geochemical, petrophysical) study of the Bazhenov Formation in the Tomsk Region using the IPGG SBRAS methodology for organic matter-rich source rock. As the thermal maturity increases from PK3 to MK2, the content of 'free micro oil' in source rock's pore spaces has been observed to increase. In the same time, there are modifications to the composition of bitumoids (chloroform source rock extracts) from open and closed pores at both the group and molecular levels. Even 'immature' organic matter has been establish to show a difference in bitumoids composition from open and closed pores, which increases as it enters the main phase of oil formation.
D.V. Epishkin1,2, N.I. Zorin3, G.R. Muradyan4, A.G. Yakovlev4 1Geoelectromagnetic Research Center, Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences, Troitsk, Russia, 2STC Nord-West, Moscow, Russia, 3Center of Geophysics, Harbin Institute of Technology, Harbin, China, 4Department of Geology, Lomonosov Moscow State University, Moscow, Russia
Keywords: airborne electromagnetics, VLF-EM, RMT, UAV.
The practical feasibility of high-precision measurements of magnetic fields from remote radio transmitters in motion, including on unmanned aerial vehicles, has been demonstrated. The method is based on measuring the Euclidean norm of the full complex magnetic field vector, which makes the results independent of the sensor system's orientation. To compensate for instabilities in the primary field, normalization is performed using a synchronized signal from a stationary base station. Additional accuracy is ensured through pre-flight sensor calibration and post-processing with spatial smoothing filters. Field tests confirmed good reproducibility, with discrepancies between repeated passes below 0.5% of the signal level. In addition, magnetic field maps obtained at different altitudes show strong internal consistency and correlate well with archived ground-based inductive electromagnetic survey data.
S.M. Zhmodik, E.V. Lazareva, V.A. Ponomarchuk, A.V. Tolstov, E.V. Airiyants, V.V. Sharygin, B.Yu. Saryg-ool, D.K. Belyanin, K.A. Musiyachenko, N.S. Karmanov
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Tomtor massif of alkaline rocks and carbonatites, carbonatite breccias, carbonates, pyrochlore-group minerals, REE-fluorocarbonates, C and O isotopes
Carbonatite breccias (CBs) were discovered in the Tomtor Massif (Complex) (TM), which hosts the largest REE-Nb-Sc-Y ore deposit, by holl G2 in the northern Buranny area. CBs are petrographically complex rocks consisting of fragments of dolomite, dolomite-ankerite, ankerite and calcite carbonatites with significant contents of F-REE carbonates, pyrite, and fluorite. CBs show signs of fragmentation of carbonatites and calcite rocks, as well as the movement of these fragments by younger melt-brine enriched in CO2, F, S, and REE, and its interaction with the fragments. The studied rocks are classified as magmatic-fluidogenic and fluidogenic breccias, which provide a unique source of information on the rock composition and processes occurring at deep levels of the TM. The distribution pattern of trace elements in the KB, presented in spider diagrams, largely corresponds to the distribution of these elements in carbonatites and uniquely rich Nb-REE ores of the upper ore horizon of the TK. Spider diagrams reveal enrichment in Th, Nb, La, Ce, and Nd and depletion in U, K, Sr, Zr, Hf, and Ti, as in other carbonatite complexes of the world (including those with breccias). The REE distribution shows enrichment in MREE and HREE. The formation of the KB is accompanied by the crystallization of REE minerals with a composition unique to the TK, primarily synchysite-(Ce), parisite-(Ce) and/or bastnaesite-(Ce), cebaite-(Ce), and burbankite. Crystallization of REE-fluorcarbonates is associated with the process of dolomite replacement by ankerite, on the one hand, and the maximum amount of these minerals, as well as cebaite-(Ce) and burbankite, is recorded in calcite rocks in association with fluorite and pyrite, on the other hand. It is shown that the position of the δ18O and δ13C‰ composition points in KB fragments and in the interfragmentary space form a dependence with a high correlation coefficient value, close to the trend characterizing the process of mixing of C and O isotopes of carbonatites and sedimentary carbonates. However, this conclusion contradicts the data on high contents of REE, Nb. P and other elements typomorphic for carbonatites with increasing δ18O and δ13C‰ values and is a result of the transformation of carbonates by a low-temperature deuteric fluid. For the first time, the obtained comprehensive data on KB allow us to consider these formations as a new type of mineralization for TK.
Y.V. Kiselnikov1, E.N. Perova2, V.F. Proskurnin1, А.G. Shneider1 1Karpinsky geological research Institute, Saint Petersburg, Russia
2Saint Petersburg State University, Saint Petersburg, Russia
Keywords: Central Taimyr accretionary belt, Borzova river gold ore cluster, contact metamorphism, spessartine, mineral geothermometry, K-Ar geochronology
The metamorphic rocks in the North Eastern Taimyr region represent a consequential result of its complex geological history. Series of metamorphic processes were associated with the formation of lode copper and noble metals mineralization. The aim of this study is to investigate the type and degree of metamorphism experienced by the host basic volcanic rocks in the ore cluster. We have identified three stages of metamorphic process: the first stage led to formation of actinolite and sodium plagioclase paragenesis (with its chemical compositions corresponding to temperature about 400 °С) the second stage resulted in crystallization of hornblende, plagioclase, spessartine-almandine garnet, biotite, feldspars (oligoclase-andesine and K-Ba types) and various Fe-Ti phases (mineral geothermometers indicate the highest temperature range of 450-600 °С) and the final stage produced clinochlore, pyrite and fluorapatite (330-290°С with AlIV contents in chlorite). We interpret the studied rocks as hornfels on the basis of highly discordant contours of the aureole, the compositions of the garnet (spessartine is predominant component), and K-Ar ages of biotite (253 ± 5 Ma) and plagioclase (239 ± 8 Ma), which coincide with the time of Late Paleozoic-Mesozoic post-collisional granitoid magmatism. The absence of schistosity, disequilibrium assemblages, and abundance of volatile-rich minerals (containing F-, [OH]- and [SO4]2-) also indicate their contact origin. The discovered aureole includes the known Cu-Au-Ag veins and metasomatic occurrences, the age of which is therefore late- or post-metamorphic. We confirm our colleagues’ early suggested hypothesis about the impact of a hidden granitic massif on the host rocks and consider the high metamorphic grade to be a natural boundary for the ore cluster.
A. B. Vrevsky, A. B. Kuznetsov, A.V. Yurchenko
Institute of Precambrian geology and geochronology, Russian Academy of Sciences, St-Petersburg, Russia
Keywords: Fennoscandian shield, Paleoproterozoic, Inari Terrane, Kaskama Formation, komatiite-tholeiite association, Sm-Nd systematics
This paper deals with new geological, mineralogical, geochemical (major, trace, and rare earth elements) and Sm-Nd isotopic data for the unique Kalevian (1923-1926 Ma) komatiite-tholeiite association for the first time identified in the supracrustal Kaskama Formation from the Inari Terrane of the Kola-Norwegian region Fennoscandian shield.
In the massive and porphyritic komatiites, the primary (magmatic) mineral paragenesis represented by olivine 20-40%, orthopyroxene up to 5%, hornblende up to 10%, clinopyroxene 20-40% and plagioclase 20-30% was identified.
Relic igneous minerals (olivine, pyroxene) make it possible to estimate (COMAGMAT3.73 program) their liquidus temperatures in the range of 1500-1200 °С.
The komatiites of the Kaskama Formation belong to the Al-nondepleted type and are characterized by a low level of REEN content (1-2 relative to C1 chondrite), their total concentration (∑REE = 0.15-0.36 ppm) and an unfractionated distribution of REEs, which is a consequence of the generation and evolution of their primary melts outside the field of thermodynamic conditions of garnet stability.
The Zr–Y–Nb and Sm-Nd isotopic systematics of the rocks of the komatiite-tholeiitic association indicates the origin of their high-temperature primary melts from the plume source in depleted mantle (εNdT=+3.2±0.3), which is different from the mantle sources of the Jatulian-Ludicovian picrite-komatiite association of the Central-Lapland greenstone belt of Finland and the Pechenga intracratonic structure.
Considering the amphibolite facies metamorphic conditions of the Kaskama formation, it can be assumed that the komatiite-tholeiitic association is a deeply eroded (at least 10 km) section of the upper crustal volcanic apparatus.
A.N. Glukhov, E.E Kolova, R.V. Solovov, M.A. Tanchenko
North-East Interdisciplinary Scientific Research Institute of Far East Branch of the Russian Academy of Sciences, Magadan, Russia
Keywords: monzonite, sienite, chemical composition, geodynamic, U-Pb age, magmatic zone, orogenic belt, volcanic belt.
Undertaked analysis of composition of the monzonite-sienite intrusive rocks, is abundant in the area of Bilikano-Khulamrinskaya magmatic zone of Central segment of the Yana-Kolyma orogenic belt. That rocks compose of small intrusions, which cut of terrigenous strata of Inyali-Debin turbidite terrane. That contained medium quantity of silica and Al2O3, relatively high – K2O, Na2O, MgO and chemically similar with latite. By chemistry that very close to alkaline felsic intrusive rocks of Aldan magmatic province. Balance concentrations of chemical elements, pointed out to belonging this rocks, to granitoids of convergent continental margin, include syncollision volcanic arcs. Age of that, by U‒Pb zircone dating (SIMS) 84 Ma, coincide with secondary impulse of magmatic activity of the Okhotsk-Chukotka Volcanic belt. Specific chemical composition of monzonite rocks of the Bilikano-Khulamrinskaya magmatic zone, close to shoshonite and latite, determined by location far in rear volcanic belt, at 200 km from axis zone of that, on the sialic basement, presented by turbidite sedimentary rocks.
P.S. Martyshko, D.D. Byzov, N.V. Fedorova
Institute of Geophysics, Ural Branch of the Russian Academy of Sciences
Keywords: Gravitational and magnetic anomalies, inverse problems, Kraka massif
The paper describes methods for three-dimensional interpretation of gravity and magnetic anomalies taking into account the relief of the earth's surface. Parallel algorithms for solving direct problems of gravimetry and magnetometry (calculating field values from sources) are implemented in software for personal computers with graphic accelerators. Based on these algorithms, methods for solving inverse problems on correctness sets have been developed. When modeling, anomaly sources of arbitrary shape are approximated by a dense regular grid, the elements of which are parallelepipeds. Methods for identifying anomalies and localizing sources in the earth's crust, calculating their physical parameters have been applied in modeling the structure of the Kraka ultramafic massifs in the Southern Urals with an area of 50x80 km2. The height of the mountain ranges in this
area reaches 1043 m, and the difference in relief heights is more than 500 m.
1 VIRG-Rudgeofizika Ltd., St. Petersburg, Russia
Keywords: induced polarization, mechanisms and models of rock polarization, stationary polarizability, interphase electrical potential
Unique relationships between the parameters of induced polarization (IP) and the structure of interphase and pore space of rocks provide high interest to applied science — ensures continuous expansion of the scope of the method. The physico-chemical theory of the phenomenon of IP rocks has gaps. This is due to the complex nature of the processes that occur in rocks and produced secondary electric fields. Laboratory studies continue to be the main source of new knowledge about the mechanisms and processes occurring in rocks when an electric field is applied. In recent decades, several new hypotheses, models, and mechanisms of IP for rocks with electron-conducting mineral (EM) inclusions have been proposed. The paper describes the key features of IP mechanisms. These mechanisms are actively discussed and used to interpret IP data collected in the laboratory and field. This paper presents the results of an experimental laboratory study on the IP of interface "shungite-porous moisture", conducted on a synthetic model of rock with EM inclusions. Based on voltametric measurements, we have identified the main characteristics of shungite's polarization in an aqueous NaCl solution. An estimate is given of the magnitude of exchange currents, the dynamics of polarization at the interphase boundary at different current densities, and the relaxation of the surface electric potential. For the first time, we present measurements of electric currents flowing in the model and within the shungite inclusion - the IP currents. It has been proven that the relaxation of the electric field in the model and the IP currents have identical dependencies. The proportionality between the polarization magnitude of shungite inclusions and the normal current component on the interface between shungite and moisture has been experimentally verified. The data obtained and published suggest that the mechanism of electrode polarization of EM inclusions in rocks plays a significant role. A probable mechanism for polarization of the interphase "EM-pore moisture" in rocks has been presented.
A.Yu. Gladenkov1, A.Yu. Kazansky1 1 Geological Institute of Russian Academy of Sciences, Moscow, Russia
Keywords: Oligocene, diatoms, West Kamchatka, magnetostratigraphy, age of diatom datum levels
Results on the age estimates of the Paleogene diatom datums derived from the magnetostratigraphy at marine Cenozoic stratigraphic section of the Kvachina Bay, West Kamchatka, are presented. Based on a direct correlation with the Geomagnetic Polarity Scale, it was possible to determine the age of such levels between Subchron C13r (35.10 - 33.73 Ma) and Subchron C9r (27.86 – 27.44 Ma). Of greatest interest are the age dating of the first and last occurrences of Lisitzinia ornata (27.71 Ma and 27.54 Ma respectively), and the first occurrence of Rocella gelida (27.49 Ma). This is the first experience of absolute age estimates of Oligocene diatom biohorizons based on magnetostratigraphy not only in Kamchatka sections, but in the North Pacific region in general. The obtained age estimates of diatom datum levels are compared with the published estimates from the literature on deep-sea cores in various regions of the World Ocean.
This special issue of the journal, dedicated to the memory of Academician Nikolai Leontievich Dobretsov, features articles reflecting the development of his research and ideas in areas within his scientific interests. The diversity of N.L. Dobretsov's scientific interests determined the broad range of topics covered in the articles presented. This range encompasses tectonics, deep geodynamics, the interaction of plate tectonics and plumes, metamorphism, including ultrahigh-pressure metamorphism in subduction zones, structural patterns of geomagnetic and gravitational fields and their relationship to plume magmatism, and unique mineral deposits.
Yu.N. Palyanov1,2, Yu.M. Borzdov1, I.N. Kupriyanov1, A.F. Khokhryakov1,2, Yu.V. Bataleva1 1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: diamond, experiment, high pressures, metal-carbon melts, mantle, fluids, diamond genesis.
Natural diamonds are polygenic and form over a very wide range of P-T parameters, crystallization medium compositions, and oxygen fugacity. As has been demonstrated in recent years, the genesis of some diamonds is directly related to their crystallization from metal-carbon melts. Since natural mineral-forming processes are highly likely to involve various components characteristic of mantle environments, it is relevant to analyze the results of experiments on the influence of fluids of the C-O-H-N-S system on the crystallization features and indicator properties of diamond. The experimental data presented in this review demonstrate that increasing the concentration of fluid components (N, O, S, H2O, CH4-H2) at constant P-T parameters inhibits diamond crystallization processes in metal-carbon melts and ultimately leads to the formation of metastable graphite instead of diamond. Increasing P and T reduces the inhibitory effect of impurities and expands the diamond crystallization region. The main patterns of specific changes in the morphology, defect-impurity composition, and internal structure of diamond crystals are revealed, depending on the type and concentration of impurity in the crystallization medium. It is demonstrated that impurity-induced specific changes in diamond morphology and trends in nitrogen concentration in diamond are indicative of crystallization conditions and provide a basis for reconstructing diamond formation processes under reducing conditions in the metal-bearing mantle.
The study of the composition and crystallization conditions of olivine in kimberlites is of great importance for understanding the processes of their petrogenesis and predicting diamond potential. The aim of this study is to investigate the origin of the least studied generation of this mineral – late high-magnesium olivine. The material for the study consisted of samples of unaltered kimberlites from the Udachnaya-East pipe, where all generations of olivine are preserved. Results from scanning electron microscopy and microprobe analysis showed that high-Mg olivine exhibits the following variations in chemical composition: Mg# (Mg/(Mg+Fe2+)×100, mol. %) 93.3-98.7, 0.01-0.05 wt. % NiO, 0.12-1.88 wt. % CaO, 0.18-0.94 wt. % MnO. This olivine forms a paragenetic association with late magmatic minerals of kimberlites: magnetite, perovskite, apatite, monticellite, sodalite, phlogopite, djerfisherite, and calcite. The following forms of high-Mg olivine were identified: individual grains (the first finding in kimberlites), rinds, daughter phases within melt inclusions, phases in fractures earlier olivine generations, and in the interstices of microxenoliths. It was found that its crystallization occurred from alkaline-carbonate-chloride melts. The temperatures and oxygen fugacity values of the crystallization of high-Mg olivine can be estimated semi-quantitatively at 670-780 °C and +3.6 - +7.4 log. units ΔQFM.. The obtained data indicate that such olivine crystallized from evolved kimberlitic melts, which contradicts previously proposed models suggesting the formation of this olivine from fluids or during the serpentinization of kimberlites.
N.Yu. Groshev, A.M. Sushchenko, D.A. Gabov, Y.E. Savchenko
Geological Institute, Kola Science Centre RAS, Apatity, Russia
Keywords: kotulskite, platinum group minerals, typomorphic mineral, PGE deposits, Kola Peninsula.
Kotulskite PdTe – the most abundant palladium mineral in platinum-group element (PGE) deposits of the Fedorova-Pana Layered Complex (FPC). This paper presents new data on the noble metal paragenesis and chemical composition of kotulskite from the North PGE Reef at the Peshempakhk target. At this target, the North Reef, extensively explored at the Kievey deposit, extends eastward. Low-sulfide mineralization containing up to 15 g/t PGE + Au outcrops here but does not form ore bodies at depth. The study aims to identify mineralogical distinctions between the discontinuous mineralization at Peshempakhk and the ore bodies of FPC deposits. 890 grains of platinum-group minerals and Au were studied in polished sections using electron microscopy, including energy-dispersive X-ray microanalysis; kotulskite was confirmed by Raman spectroscopy against a synthetic analogue. The noble metal assemblage at Peshempakhk comprises (in relative vol. %): kotulskite (38 %), isomertieite (22 %), sperrylite (18 %), stibiopalladinite (11 %), hollingworthite (3 %), and gold (3 %). The noble metal paragenesis of the target differs from that of the main FPC deposits, where sulfides and tellurides of PGE predominate, namely braggite, vysotskite, merenskyite, moncheite, and kotulskite. Kotulskite at Peshempakhk averages 8.4 wt. % Bi, whereas deposits exhibit a more complete kotulskite-sobolevskite solid solution series with average Bi concentrations between 13.3 and 20.2 wt. %. Additionally, the studied kotulskite includes an antimony variety containing up to 10.3 wt. % Sb. The simultaneous presence of the two kotulskite types points to an origin under the most low-temperature conditions of a magmatic setting. Thus, the noble metal paragenesis and composition of kotulskite from the FPC PGE mineralization are its key typomorphic features. These results can be used to forecast ore zones in similar settings.
A petrological, geochemical and geochronological study of gabbro intrusions of the Utlyktash complex in the northern part of the West Magnitogorsk zone of the Southern Ural was conducted. The studied intrusions are confined to the margins of the Imangulovo syncline of syncollisional origin and its periphery. The age of Uraz gabbroic massif according new LA-ICP-MS data is 333±3 Ma. The geochemical features and Nd-Sr isotopic composition of the Utlyktash complex rocks reflect a weakly depleted mantle PM-like source for gabbroids with subsequent significant magma fractionation and minor crustal assimilation (up to 6%). Thermodynamic modeling supports the fractionation model of a single parental melt from which all the studied gabbro bodies crystallized. ID-TIMS and LA-ICP-MS U-Pb zircon dating (ranging from 0.44 to 2.73 Ga) indicates the involvement of ancient continental crust and ophiolitic material from the zone of the Main Ural Fault, along which the Magnitogorsk island-arc terrane was thrust onto Laurussia paleomargin. The geological position of the Utlyktash complex and its geochemical correlation with basalts from the central part of the Magnitogorsk megazone suggest formation during syncollisional rifting in the early Carboniferous period, preceding the assembly of the Laurasia supercontinent.
E.A. Bogdanov1,2, N.Yu. Matushkin1,2, A.E. Vernikovskaya1,2, A.V. Travin3 1Novosibirsk State University, Novosibirsk, Russia
2Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia
3V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia
Keywords: Ophiolite, 40Ar/39Ar geochronological data, accretion, late Mesoproterozoic, Neoproterozoic, oblique collision, Tatarka-Ishimba suture zone, Yenisei Ridge
We report results of geostructural, mineralogical, petrographic, geochemical and geochronological (40Ar/39Ar) investigations of ophiolites in the northern and southeastern fragments of the Tatarka-Ishimba suture zone of the Yenisei Ridge combined into the Rybnyi-Panimba belt. They consist of massive and pillow-lava metabasalt, massive and layered metagabbro and metadolerite, and represent fragments of the upper part of the oceanic crust. They formed in a mid-ocean ridge or marginal sea setting from depleted mantle sources corresponding to components of N-MORB and E-MORB geochemical types. We propose a model for the tectonic history of emplacement of ophiolites on the margin of the Siberian craton in the Neoproterozoic time. At the Meso–Neoproterozoic boundary (Stenian–Tonian), 1051–916 Ma, the thrust structure was formed and the oceanic crust fragments (ophiolites) were accreted to the passive margin of the Central Angara Terrane (microcontinent). The subsequent convergence and collision of this microcontinent with the Siberian craton (786–749 Ma) caused the formation of strike-slip/thrust deformation in the rocks of the Tatarka-Ishimba suture zone including ophiolites. In the Cryogenian (708–700 Ma), strike-slip and reverse fault deformations occurred in these rocks due to a new episode of tectonic activity caused by the transition between convergent settings – end of the collision and start of the active continental margin.
M.Y. Shumskayte1, T.A. Yanushenko1, V.G. Smirnov2, N.A. Golikov1 1Trofimuk Institute of petroleum geology and geophysics SB RAS, 630090, Novosibirsk, Koptug ave., 3, Russia
2Nikolaev Institute of inorganic chemistry SB RAS, 630090, Novosibirsk, Lavrentiev ave., 3, Russia
Keywords: Gas hydrate, sorbed water, nuclear magnetic resonance, longitude and transverse relaxation times
This study is developed to estimate the proportion of sorbed water converted to ice and hydrate during the interaction of wet sand samples with methane by NMR relaxometry method. It was demonstrated that a thin film of tightly bound water exists in small pores at the rock-fluid interface. This water does not freeze at the subzero temperatures achieved during the experiment; its quantity remains constant, regardless of the sample's water content. The amount of tightly bound water, as well as the amount of water converted to ice and hydrate, was calculated for all samples. Based on the known hydrate stoichiometry, the amount of methane converted to hydrate was calculated. Based on the obtained data, the optimal water content in the sample was determined, which would result in the greatest amount of hydrate formation.
V.V. Arapov1 *, A.A. Emanov1, 2, A.F. Emanov1, A.V. Fateev1, 2 1Altay-Sayan Branch of Geophysical Survey, Siberian Branch of the Russian Academy of Sciences, pr. Novosibirsk, Russia
2Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: seismic quality factor, intrinstic attenuation, scattering attenuation, earthquake, Qopen, Chui-Kurai zone, Altai mountains.
The attenuation of seismic waves and its components in the Earth's crust of the Mountain Altai Chui-Kurai zone has been studied by the method of code envelope inversion [Sens-Schönfelder, Wegler, 2006]. The analysis used waveforms of earthquakes with a magnitude ML > 2.5, recorded by a network of stationary and temporary stations of the ASGSR RAS within the studied region. As a result, the contribution of Qi-1
absorption and Qsc-1 scattering to the overall Qt-1
attenuation of the main structures of the region was determined, and the spatial distribution of the Qt parameter, as well as the seismic albedo B0, was estimated. The dominance of the absorption contribution over scattering in the overall attenuation of seismic waves is shown. The obtained values of the seismic Q-factor parameter make it possible to carry out an accurate calculation of the moments of magnitudes and an assessment of the focal parameters of earthquakes, as well as more accurately calculate artificial accelerograms, etc.
A.A. Dobrynina1,2, A.V. Sankov1, I.V. Buddo1, I.A. Shelokhov1, V.A. Sankov1 1Institute of the Earth’s crust Siberian Branch of the Russian academy of science,Irkutsk, Russia
2N.L.Dobretsov geological institute Siberian Branch of the Russian academy of science,Ulan-Ude, Russia
Keywords: Arctic, passive seismic, ambient noise, upper part of the section, pingo, hard to recover reserves.
The paper provides a brief overview of methods based on the analysis of natural ambient noises of the Earth (passive seismic exploration methods): methods of spatial autocorrelation, seismic interferometry and spectral ratios of seismic noise components, as well as their application to studying the structure and properties of the upper part of the section in Arctic conditions. The analysis and interpretation of the upper part of the section through pingos in the Arctic zone were carried out using passive seismic methods (spectral component ratios). The resulting two-dimensional sections reflect the horizontal layered structure of the upper part of medium – four main layers are clearly visible on the profiles which may be interpreted as the upper sedimentary layer, the basement layer, and two intermediate layers that differ in velocity characteristics. The section is disturbed by vertical and inclined heterogeneities that extend from faults in the basement to the surface and are characterized by high anisotropy of properties and reduced rigidity. The spatial correlation of the identified subvertical heterogeneities with the position of pingos on the surface suggests that these areas represent weakened zones, possibly fault zones or conductive channels. Based on the results of the review of scientific publications, a conclusion was made about the reliability of the results obtained by passive seismic methods, which is confirmed by other independent geophysical research methods. Passive seismic methods demonstrate high efficiency when working in hard-to-reach areas, such as the Arctic zone, since they do not require long-term installation of an observation network, and when using spectral ratio methods, they do not require a large number of seismic stations. They are especially useful when studying hard to extract resources characterized by a complex structure of the upper part of the section (the first meters), since they allow for the rapid study of the upper part of the section for depths from the first meters to tens of kilometers during reconnaissance work without significant financial and labor costs. From an environmental point of view, passive seismic methods are the most gentle, as they are non-invasive and non-destructive.
The article presents the results of numerical modeling and inversion of Lateral Logging (LL) data for determining the geoelectrical parameters of oil-and-gas-saturated reservoirs in the northern fields of Western Siberia. The research is based on the analysis of synthetic LL signals calculated for a typical model of the Achimov deposits of the Yamburg field, which are characterized by small reservoir thickness. The influence of changes in parameters such as the formation resistivity, the invaded zone thickness, and depth shift on the LL signals is considered. An assessment of the accuracy of reservoir parameter recovery using two-dimensional numerical inversion was carried out, areas of equivalence were identified, and recommendations for error minimization are proposed. The results showed that the greatest sensitivity of the LL signals is observed to changes in the formation resistivity and the invaded zone thickness, with the error in determining the formation resistivity being up to 12%.
Valovayam and Tymlat adakites were formed during subduction of the Miocene oceanic lithosphere of the Komandorsky Basin beneath the North Kamchatka followed by the interaction with mantle wedge peridotites. Post-collisional adakitic dacites from the Bakening paleo-volcano (Central Kamchatka) are related to the destruction and melting of the Mesozoic Kronotsky microplate paleo-slab due to the influence of hot sub-slab asthenospheric mantle after the collision of the Kronotsky island arc. Minerals and volcanic glass in Kamchatka adakites contain predominant Cu-Ag-Au alloys and silver chloride microinclusions along with various chalcophile sulfides, native metals, alloys, oxides and carbonate hydroxides. Microinclusion assemblages in adakites are broadly comparable to the ore mineral associations in epithermal and porphyry deposits from the Russian Far East. Kamchatka adakites display elevated silver and gold contents in comparison with back-arc basin and volcanic arc lavas, which could be sourced from the metamorphosed oceanic crust and metalliferous pelagic sediments in the subducted slab. We conclude that adakites associated with subduction of the young oceanic lithosphere (North Kamchatka) and the old lithospheric slab tear and break-off (Central Kamchatka) can be magmatic precursors for the copper-gold-silver mineralization in the Kamchatka region. We also propose that adakite-related metallogenic processes may occur in the other convergent plate margin settings, for example, in the flat slab subduction environments.
A.I. Kozhurin1,2, T.K. Pinegina2 1Institute of Volcanology and Seismology of Far Eastern Branch of RAS, Russia
2Geological Institute of RAS, Moscow, Russia
Keywords: Kamchatka, Aleutian Arc, arc-arc collision, active faults
The article presents data on active faulting in the Kamchatsky Peninsula (Kamchatka, Russia) located between the converging Aleutian and Kamchatka Island arcs. Convergence of the arcs leads to shortening of the Kamchatsky Peninsula, transverse to Kamchatka, and is accomplished by underthrusting of the blocks involved in the collision – of the Aleutian Arc under the Kamchatsky Peninsula and that of the Kamchatsky Peninsula under Kamchatka. It is shown that underthrusting as the way absorbing convergence is also characteristic for larger collision zones, as in case of collision of the Indian and Arabian plates with the Eurasian plate. In all the cases, the plate (block) underthrusts, in the rear of which there is a source of movements.
V.N. Sergeev1, A.A. Soloviev1,2, D.V. Kudin1, R.V. Sidorov1, I.M. Aleshin1,2, F.V. Perederin1,2, K.I. Kholodkov1,2, D.K. Mokrov2, A.A. Kamaev1, A.A. Grudnev1,2, V.V. Kabrov1, V.A. Atabekyan3 1 Geophysical Center of the Russian Academy of Sciences, Moscow, Russia
2Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences, Moscow, Russia
3 Institute of Geology and Mining of Fossil Fuels (IGiRGI JSC), Moscow, Russia
Keywords: Geomagnetic measurements, Earth's magnetic field, measurement methods, aeromagnetic survey, ground-based magnetic survey, magnetic field components, magnetic anomalies, Earth's magnetic field models verification
A complex of field geomagnetic studies is proposed, aimed at assessing the accuracy of the Earth's magnetic field models using instrumental determinations of the geomagnetic vector elements in the given location. The set of measurements consists of aeromagnetic survey using unmanned aerial vehicles, as well as ground-based measurements, including pedestrian magnetic survey and the absolute measurements of magnetic declination and inclination. The developed measurement technique allows solving the problem of determining the Earth's magnetic field in areas with insufficient coverage by stationary ground-based geomagnetic observations. The results of applying the developed technique are presented. As a case study, the territory of the central part of the West Siberian platform is chosen. The results confirm the efficiency of the proposed approach for conducting measurements over restricted time due to seasonal and weather conditions. The obtained data are highly accurate, which makes the proposed technique attractive for determining the geomagnetic secular variation in an arbitrary area.
A.G. Sokol1, O.A.Kozmenko1, A.N. Kruk1 1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: subduction, mantle, sediments, fluid, melt, trace elements, arc magmas, metasomatism
Experiments were carried out with naturally-doped pelite containing 3 wt.% CaCO3
in the pressure range of 3.0-7.8 GPa and temperatures of 750-1090 °C, so that the total carbonate content reached 7 wt.%, similar to that in the model global averaged subducted sediment (GLOSS). As a result of dehydration and decarbonation of the pelite under thermal conditions of subduction zones, residue is formed, consisting of garnet, clinopyroxene, phengite, coesite, ±Mg-Fe carbonate, and kyanite, along with accessory minerals such as rutile, monazite, and zircon. Additionally, a mobile phase is generated, which significantly evolves with increasing P-T parameters along the warm subduction geotherm. At 3.0 GPa and 750 °C, a granite-like melt (H2O+CO2 - 19 wt.%) enriched in SiO2 and Al2O3 is formed, with a K2O/Na2O ratio of 1.2. At 5.5-7.8 GPa and 850-940 °C, a supercritical fluid-melt (H2O+CO2 around 40 wt.%) enriched in SiO2 and K2O, but poor in Al2O3, is produced, with a K2O/Na2O ratio reaching 9.5. The supercritical fluid-melt (SCFM) forming in the carbonate-bearing pelite can effectively transport LILE and LREE, including trace elements that are markers for both deluted aqueous fluids (Ba and U) and markers for granite-like melts (Sr, LREE, and Th). During the fractionation of trace elements, important roles are played by host minerals: phengite (LILE), monazite (LREE), and rutile (HFSE). An increase in carbonate concentration in the pelite leads to a slight decrease in the partition coefficients of the most incompatible elements due to the increase of the mobile phase fraction and concentration CO2 within it. The SCFM obtained in equilibrium with rutile-bearing residue retains the characteristic negative Nb anomaly typical of marine sediments and is capable of transmitting it to arc magmas if involved in their generation.
M.I. Epov1, N.N. Mikhailov2,3,4, V.N. Sokotuschenko2, O.M. Ermilov2,5 1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk,Russia
2Gubkin Russian State University of Oil and Gas, Moscow, Russia
3Institute of Oil and Gas Problems, Russian Academy of Sciences, Moscow, Russia
4M. V. Lomonosov Moscow State University, Moscow, Russia
5LLC “Gazprom Dobycha Nadym”, Nadym, Russia
Keywords: hard-to-recover reserves, low-permeability reservoirs, nonlinear filtration, well flow rate, drawdown pressure, skin factor, formation damage, indicator curves, hysteresis, power-law filtration.
Concerning low-permeability reservoirs with hard-to-recover (HTR) hydrocarbon reserves, we comprehensively analyzed the influence of nonlinear reservoir processes on well flow rate–drawdown pressure relationship.
We identified new nonlinear relationships between the flow rate of low-permeability reservoirs and reservoir drawdown (indicator curves). The nonlinearity of the indicator curves is due to the combined effects of nonlinear filtration, technogenic reservoir change, and the dependence of formation damage parameters on drawdown. The applied approach allowed us to find out qualitatively new regularities in the relationship between flow rate and drawdown in low-permeability reservoirs. A well productivity analysis revealed hysteresis in the indicator curves and a shift in critical drawdown values when considering both formation damage and filtration nonlinearity. It was established that the combined effects of nonlinear filtration and damage effects lead to an additional flow rate reduction of 25–40% compared to separately considering each of these effects. The obtained results are of practical significance for optimizing the development of low-permeability reservoirs with HTR reserves and for predicting their productivity.
A.A. Shiryaev1, E.F. Vasilev2, A.L. Vasil’ev3,4, V.V. Artemov3, N.V. Gubanov5, D.A. Zedgenizov5 1Frumkin Institute of physical chemistry and electrochemistry RAS, Moscow, Russia
2Saint Petersburg mining university, Saint Petersburg, Russia
3 Shubnikov Institute of Crystallography, Kurchatov Complex of Crystallography and Photonics, National Research Centre "Kurchatov Institute," Moscow, Russia
4Moscow Institute of Physics and Technology, Dolgoprudny, Russia
5Zavaritsky Institute of Geology and Geochemistry UB RAS, Ekaterinburg, Russia
Keywords: diamond, Y-defect, spectroscopy, transmission electron microscopy
The paper presents results of investigation of a natural Ib-IaA diamond containing Y-defects from Yubileinaya kimberlite pipe. Analysis of spatial distribution of A and C defects and intensity of IR absorption at Raman frequency (1332 сm-1) reveals anticorrelation between these defects. Transmission electron microscopy of a zone with abundant Y-defects shows presence of dislocations in various configurations and numerous clusters of point defects generated by non-conservative dislocation movement. Extended defects with shape resembling thin (1-3 nm) rhombic plates with the largest dimension up to 5-20 nm. Analysis of contrast of these defects shows that they represent nanosised voids (vacancy clusters). It is suggested that the defects were formed by annihilation of dislocation dipoles with subsequent growth by consumption of vacancies produced by non-conservative motion of dislocations. Upon excitation by 787 nm laser, in region 800-900 nm of photoluminescence spectra numerous narrow lines are observed, their intensity and position show irregular temporal variations. Such behavior (blinking) was earlier note for hydrogenated nanodiamonds. It is suggested that unusual behavior of the luminescence lines may be explained by recombination processes on internal walls of the voids.
S.Yu. Skuzovatov1, V.S. Shatsky1-2, A.L. Ragozin2 1Vinogradov Institute of Geochemistry, Russian Academy of Sciences, Siberian Branch, Irkutsk, Russia 2Sobolev Institute of Geology and Mineralogy, Russian Academy of Sciences, Siberian Branch, Novosibirsk, Russia
Keywords: Central Asian Orogenic belt, Kokchetav massif, subduction, collision, high-pressure metamorphism, eclogites, trace elements, Nd–Sr isotopes, P–T–trends
Among fine- and medium-grained eclogites, which are predominant within the Kokchetav subduction-collision zone (Kazakhstan), metasedimentary mélange in the Sulu-Tyube area bears rare porphyroblastic eclogites, which are juxtaposed with host rocks of the Zerenda series. The assemblage of garnet cores граната (XAlm
up to 0.59, XPrp from 0.08) with epidote–clinozoisite (XCzo=0.36–0.90), amphibole, ilmenite, titanite and rutile, prograde garnet zonation imply nearly isothermal burial of rocks down to 11.5–20.5 kbar and 535–570°С. The growth of high-Mg garnet rims (XPrp up to 0.31) in paragenetic relations with omphacite (XJd up to 0.35) stem the second stage with nearly isobaric heating up to 645°С at 21.5 kbar, which, for individual samples, reach 620–690°С. Fine- and medium-grained eclogites with uniform textures and weakly zones garnet, which contains inclusions of omphacite (XJd=0.20÷0.40), rutile and quartz, were formed during heating and limited pressure increase (580–660°С and 16–19 kbar). Variations of equilibrium temperatures (620–730°С) indicate their different position within the structure of subducted lithosphere. MORB-like signatures of eclogites correspond to those of low-Ti tholeitic rocks, but fine-grained rocks are depleted in Nb-Ta and Eu and enriched with Th at radiogenic Sr isotope composition Sr (87Sr/86SrI 0.71181–0.72935) and moderately depleted Nd isotopes (εNd(530) +0.5÷+4.2), whereas porphyroblastic rocks, rehydrated during exhumation, reveal juvenile Nd-Sr signatures (87Sr/86SrI 0.70212–0.70426, εNd(530) +6.6÷+7.2). Contrasting features of eclogites result from subduction burial of rifted margin of the Kokchetav microcontinent or more ancient continental unit, which included variably contaminated N-MORB an E-MORB basites, and involvement of oceanic or eroded Cambrian island-arc rocks into the same process. Principal differences in fluid regimes of subduction and exhumation were governed by proximity of hydrated subduction channel for porphyroblastic rocks and weak fluid permeability of continental lithosphere – for their fine- and medium-grained counterparts.
Е.А. Kostyreva1, I.S. Sotnich1
Trofimuk Institute of Petroleum Geology and geophysics of Siberian branch of Russian Academy of Sciences (IPGG SB RAS), Novosibirsk, Russia
Keywords: Bitumoids, hydrocarbon biomarkers, Anabar-Khatanga petroleum province, organic geochemistry
The article presents the results of the detailed modern geochemical investigation of a representative (both by area and by section) collection of core material from Permian deposits of the Anabar-Khatanga petroleum province. The organic matter of Permian deposits has been firstly shown to be polygenous within all the section and have a different thermal maturation level (stages MC11-AC). It also has exhausted oil and gas generative potential in the most part of the section. The studying deposits contain paraautochthonous and allochthonous bitumoids (chloroform source rock extracts) in addition to autochthonous (syngenetic) ones, that can be the evidence of intensively occurring migration processes. There are also bitumoids with traces of biodegradation in Early Permian deposits from the Yuzhno-Tigyanskaya and Nordvikskaya wells.
Reutsky V.N.1, Zedgenizov D.A.2, Ragozin A.L.1, Kalinina V.V.1, Zemnukhov A.L.3 1 Sobolev Institute of Geology and Mineralogy Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia. 2 Zavaritsky Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences, Ekaterinburg, Russia. 3 Almazy Anabara AO, Yakutsk, Russia.
Rounded diamonds of the variety V (Yu. L. Orlov’s classification) are endemic to placers in the northeastern Siberian Craton. Their primary source has not yet been established, making it difficult to estimate the age of these crystals. Geochemical features (δ13C from -17 to -25‰, Nppm from 1200 to 2000) indicate that subducted material contributed to their formation. Studied diamond intergrowth consist of crystals with δ13С = -20.8 and -20.7‰ and nitrogen content of 1693 - 2036 and 1568 - 1953 at. ppm, correspondingly. Zircon inclusions with δ18O = 7.9-8.8‰ found in one of these diamonds have a U-Pb age of 262.5 ± 2.7 and 232.6 ± 3.0 Ma. The zircon inclusion with an older age may belong to the early stages of formation of the intergrowth or to the diamond crystal fragments that are part of the intergrowth. Alternatively, it may be protogenetic. We suggest that the crystallization substrate and source of the carbon of this diamond was a fragment of subducted oceanic crust containing organic sediments and hydrothermally altered basalts. The diamond studied was brought to the surface no earlier than the Triassic episode of kimberlite magmatism on the Siberian craton.
1Geological Institute, Russian Academy of Sciences, Moscow, Russia 2Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia 3Moscow Institute of Physics and Technology, Dolgoprudny, Russia 4Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, pr. Akademika Koptyuga 3, Russia 5Novosibirsk State University, Novosibirsk, Russia 6VNIIOkeangeologia, St. Petersburg, Russia 7Polar Geophysical Institute, Murmansk, Russia 8Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
We provide a brief description of the main structures in the Eastern Arctic, in the evolution of which two major stages have been distinguished and considered: the late Paleozoic–early Mesozoic and the Late Jurassic–Early Cretaceous. We have established the synchronicity of tectonic events on the Arctic margins of Northeast Asia and Arctic Alaska and within the structures of the Amerasia Basin, indicating the existence of a cause-and-effect relation between the compression (fold-and-thrust structures) and extension (rifting and spreading in the Canada Basin). We have proposed the tectonic models of the formation of fold-and-thrust structures in Chukotka and Arctic Alaska and have determined their similarities and differences. Paleotectonic reconstructions have been performed for 160 and 120 Ma. We present a critical review of the concepts about the formation of the structures in the Amerasia Basin and provide a subduction-convection geodynamic model according to the analysis of seismic tomography of the mantle and regional geology and tectonics data. This model was previously used to describe the Cretaceous and Cenozoic evolution of the Arctic lithosphere at a qualitative level. The model is based on the idea of the existence of a two-tier subduction system: a horizontally extended convection cell in the upper mantle, coupled with a conveyor mechanism of subduction of the Pacific lithosphere. As a result, there is a convergence of the “outer” Pacific subduction zone and the “inner” subduction zone located inside the South Anyui and Angayucham oceanic basins, which provides their closure and subsequent collision. Under the influence of the reverse upper mantle flow, scattered deformations of the Amerasia lithosphere occur, caused by viscous dragging with flows beneath the lithosphere, which is the reason for the diversity of the structures in the Amerasia Basin and the Canada Basin in particular. In addition, the developed geodynamic model is supplemented by a tectonic and magmatic mechanism of crustal subsidence and the formation of sedimentary basins.
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