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Russian Geology and Geophysics

2018 year, number Неопубликованное

41.
CORRECTION OF EFFECTIVE VELOCITY FOR THE INFLUENCE OF STATIC APPLICATION

A.V. Novokreshchin, D. S. Rakivnenko, I. I. Karimov
Keywords: static corrections, effective velocity, RMS velocity, time to depth conversion

Abstract >>
The article considers the problem of distortion of effective velocities estimated from common depth point (CDP) gathers caused by implementation of static corrections for compensation of the influence of near surface velocity anomalies. An analytical solution of the problem of compensation of effective velocities caused by the static correction for shallow and deep velocity anomalies correction is presented. The results of numerical modeling demonstrate the efficiency of the obtained solution. A comparative assessment of the accuracy of time to depth conversion with proposed methodology, without velocity correction and other algorithms for solving the problem is provided



42.

CAMPANIAN DINOCYST OF THE NORTHERN HEMISPHERE: GEOGRAPHICAL DIFFERENTIATION AND CORRELATION POTENTIAL

N.K. Lebedeva


A.A.Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian of Sciences, Novosibirsk, Russia
Keywords: Dinoflagellate cysts, Campanian, biogeography, paleogeography, correlation
Abstract >>
The article presents the results of the analysis of the geographical distribution and taxonomic diversity of dinoflagellate cysts in the Campanian of the Northern Hemisphere. Three types of dinocyst assemblages were established based on the qualitative and quantitative assessment of their generic composition. A wide distribution of some stratigraphically important genera and species, which previously had narrower habitats, was revealed due to transgressive events, expansion of interbasin connections, and the presence of multidirectional meridional currents. The possibility of comparing the North Siberian dinocyst assemblages with those from the stratotypes containing the orthostratigraphic faunal groups of the West European and North American Campanian deposits through the ekaton sections of the Subpolar Cis-Urals and the south of Western Siberia was shown.



43.
NORMALIZATION OF MAGNETOTELLURIC SOUNDING CURVES USING SPATIAL LOW-PASS FILTERING

Sukonkin M.A., Pushkarev P.Yu.
Lomonosov Moscow State University, Moscow, Russia
Keywords: magnetotelluric sounding; suppression of near-surface distortions; normalization of MT sounding curves

Abstract >>
A significant problem of the magnetotelluric sounding (MTS) method is the influence of local near-surface inhomogeneities, which distort MTS data across the entire frequency range. These distortions complicate the analysis and interpretation of the data and, ultimately, the retrieval of information about the studied deep structures. A widely used method for suppressing near-surface distortions is the normalization of MTS curves using spatial low-frequency filtering. The aim of the article is to evaluate the effectiveness of this approach, including through the use of weighting characteristics proposed by the authors. A simple geoelectric model of the earth's crust has been compiled, containing a conductive sedimentary cover, a high-resistivity basement, and a three-dimensional conductive depression in the basement. Two model variants were considered: with a homogeneous upper part of the section and with multiple local near-surface inhomogeneities. Using three-dimensional modeling, synthetic magnetotelluric sounding (MTS) data has been calculated for a system of profiles. The data for the second model variant exhibit the effect of near-surface distortions, which leads to a shift in the MTS amplitude curves by level. To suppress the distorting effect from near-surface inhomogeneities, we used normalization of the MTS curves with smoothing filters in a sliding window with different radiuses. Various weight characteristics of the filters were used, namely: for the distance of a point from the center of the sliding window radius, for the difference in amplitude at a given point from the average in the window, and for the difference in the principal directions determined from the polar diagrams of the modulus of the principal component of the impedance tensor and the principal component of the phase tensor. In general, the experimental results showed high efficiency of normalization of the principal components of the impedance tensor and telluric tensor and lower efficiency of normalization of additional components.



44.
“INVISIBLE” GOLD ON THE ARSENOPYRITE NATURAL SURFACE OF THE NATALKA GOLD DEPOSIT (North-East of Russia): LA-ICP-MS DATA

R.G. Kravtsova, A.S. Makshakov, V.L. Tauson, N.V. Bryanskiy, S.V. Lipko
Vinogradov Institute of Geochemistry SB RAS, Irkutsk, Russia
Keywords: Arsenopyrite, surface, gold, LA-ICP-MS, XPS, distribution features, concentration levels, Natalka deposit

Abstract >>

Using the laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) complex, with the involvement of X-ray photoelectron spectroscopy (XPS), new data were obtained on the distribution features and concentration levels of “invisible” gold on the natural surface of arsenopyrite crystals from the Natalka gold deposit (North-East of Russia). It was found that the distribution of Au contents on the surface of the studied sulfide and its concentration levels are closely related to the conditions of the deposit formation. The highest Au concentrations are confined to the surface of arsenopyrite crystals of the hydrothermal stage of ore formation, and the minimum ones are found at the early metamorphic stage. The extreme instability of the gold distribution profile and its content even within the surface of a single crystal is especially pronounced in arsenopyrite of vein and veinlet-vein ores, which is due to the instability of the physicochemical parameters of the hydrothermal ore formation processes at later stages of the deposit formation. Basically, these are oxidation processes that lead to a change in the composition of the primary (as-grown) non-autonomous phases and the redistribution of gold in the surface layer of the crystal, containing highly charged forms of arsenic – As5+ and As3+. The complex and long-term metamorphogenic-magmatic genesis of the giant gold ore deposit Natalka is confirmed. High concentrations of “invisible” gold in the easily destroyed surface layer of sulfides during enrichment are of significant practical interest in the extraction of gold from “refractory” ores, increasing the quality and value of the extracted raw materials.



45.
ORDOVICIAN MARINE SEDIMENTS OF TYVA, ALTAI-SAYAN FOLDED AREA: BIOSTRATIGRAPHY, FACIES, COMPOSITION AND SPECIFIC OF FAUNAL ASSEMBLAGES AND PALEOGEOGRAPHIC LOCALITY

N.V. Sennikov, O.T. Obut, N.G. Izokh, A.V. Timokhin, I.V. Korovnikov, E.V. Lykova, R.A. Khabibulina
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia


Keywords: Tyva, Ordovician, litho-biostratigraphy, marine sedimentary and volcanic-sedimentary strata

Abstract >>
New lithological and biostratigraphic data on stratotype and paleontologically representative marine sedimentary sections of the Malinovka Group (Borlug, Tarlyk and Tamzyrin formations) in the Uyuk area of the region; Shemushdak Group (Ayangaty and Adyrtash formations) and Chergaky Group (Alavelyk Formation) in the Khemchik area of the region; Chergaky Group (Alavelyk Formation) in the Alash area of the region; Kargy Formation in the Kargy area of the region are discussed. The materials on the Sistigkhem Group (Uza, Ust’-Khamsary and Kugar formations) in the Sistigkhem area of Tyva are considered. The chronostratigraphic position of the Tarlag-Aksy Horizon has been clarified and the identification of a new Borlug Horizon has been substantiated. It has been found out that outrcops of the Tyva Ordovician marine sediments are currently located in the number of tectonically isolated blocks and are not fragments of a single paleobasin. Based on the analysis of the taxonomic composition of faunal assemblages and ichnofossils, it is suggested that the Tuvinian Alash-Khemchik, Uyuk and Kargy blocks with outcrops of Ordovician marine sediments were paleozoogeographically close to the marine paleobasins of the Gondwana group of continents. At the same time, a low migration potential of their faunal assemblages relatively to the possibilities of communication with coeval communities of the Altai Basin and of that of
2 из 48
the Siberian Platform and Taimyr was observed. The Tuvinian Sistigkhem block characterized by effusive-sedimentary sequences of the marine genesis was not only at a significant distance from the listed Siberian paleobasins, but was also separately located from the group of Alash-Khemchik, Uyuk and Kargy blocks with Ordovician marine sediments.



46.
STRATIGRAPHIC POSITION AND INTEGRATED CHARACTERISTIC OF THE UPPER VENDIAN NEMAKIT-DALDYNIAN STAGE

V.V. Marusin
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences,Novosibirsk, Russia
2Novosibirsk State University,Novosibirsk, Russia
Keywords: Vendian, Cambrian, General Stratigraphic Scale of Russia, International Chronostratigraphic Chart, small skeletal fossils, trace fossils, chemostratigraphy, Siberian Platform

Abstract >>
Nemakit-Daldynian Stage was originally introduced as a regional stage, embracing the lowermost Cambrian strata with the oldest small skeletal fossils, for the Anabar Uplift sections in the 1960s. In subsequent years, it became widespread in the works of Soviet researchers as the terminal Vendian or basal Cambrian stage or regional stage. Almost at the same time, the concept of the Manykaian Stage appeared which is close in its volume and geological meaning to the Nemakit-Daldynian Stage. Although this unit plays a crucial role for our understanding of the chronology of biotic turnovers at the Vendian–Cambrian transition, its status, age, and correlation with the Manykai Stage and units of the International Chronostratigraphic Chart (ICC) remain unclear. This research reveals a historical background revisits the stratigraphic volume and age of the Nemakit-Daldynian Stage. The integrated biostratographic, stable isotope and geochronological data shows this unit belongs to the Upper Vendian and spans the interval from the first appearance of unequivocal anabaritids (~539 Ma) to the first appearance of the Tommotian small skeletal fossils (~530 Ma). In this interpretation, the Nemakit-Daldynian Stage corresponds to the Fortunian Stage of the Cambrian System in the ICC. The base of this unit is coeval to the base of the Rovno Regional Stage of Baltica.



47.
COMPOSITION, GEOLOGICAL STRUCTURE AND FORMATION MODEL OF THE SUBDUCTION MELANGE OF THE ALAMBAY MELANGE ZONE OF SALAIR (NORTHWEST CENTRAL ASIAN OROGENIC BELT)

F.I. Zhimulev, A.V. Kotlyarov, M.A. Fidler, N.A. Bekhterev
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Ophiolites, Altai-Sayan orogen, melanges, olistostromes, subduction, accretionary prism, flysch, oceanic islands, subduction.

Abstract >>
The Alambay melange zone (AMZ) is located in the interior of the Early Paleozoic Salair orogeny (Northern part CAOB) and represent the northern extension of the Alambay-Kaim zone, Salair and the Altai Mountains. In paleotectonic terms, Salair is a part of the Kuznetsk-Altai paleo-island arc system. AMZ ophiolites are characterized by the absence of igneous rocks with the geochemical characteristics of MORB, as well as large allochthonous nappes composed of the undisturbed oceanic plate stratigraphy units. Melange complexes play an important role in the geological structure of the AMZ. Two types of melanges, serpentine and clastic, are distinguished in the AMZ. The both types of melanges contain blocks of microquartzites, basalts, limestones; also in clastic mélange a block of garnet amphibolites is found, and in serpentine melange there are blocks of gabbro. Gabbro and garnet amphibolites from AMZ melanges can be classified as island arc rocks based on their geochemical features. Chromite from serpentinized hyperbasites of the zone has an increased content of chromium and magnesium, which is also typical for chromite from suprasubduction hyperbasites. Melange basalts are characterized by high titanium and niobium contents and belong to the OIB type. There are two morphological types of the clastic melanges. The first type is characterized by the predominance of inclusions over the matrix, and the dominance of OIB basalts and limestones in the composition of the inclusions. The second type is characterized by a predominance of matrix over inclusions, and the main type of inclusions are microquartzites (metacherts). To explain the origin of AMZ melanges, the OPS melange model can be used [Wakita, 2015]. This model describes the relations between subduction melanges composition and the position of the decolement, separating subducting plate from the accretionary prism. Within this model, the first type of terrigenous subduction melange is the limestone-basalt type (ls-bs), which is the result of seamount subduction, and the second type corresponds to the sandstone-siliceous type (ss-ch). Formation of sandstone-siliceous melange corresponds to the position of the decolement along the base sedimentary layer of the subducting plate. Subduction melange formed later than 500 million years and earlier than the accumulation of the flysch Late Cambrian-Early Ordovician Green-Violet Group, which allows to estimate the age of the AMZ melange to the Late Cambrian. Wide distribution island-arc rocks as inclusion in the composition of serpentinite and clastic subduction mélanges suggests that the Cambrian subduction zone was characterized by a tectonic erosion regime, in which material from the subduction hanging wall was carried into the subduction zone. The separation faults, along which material was exhumed from subduction channel into the accretionary wedge, were located along the base of the oceanic sediment layer, at the base of the seamounts, and inside the hanging wall of the subduction zone as well.



48.
HIGH-BARIUM PHLOGOPITE FROM KIMBERLITE OF THE MALOKUONAPSKAYA PIPE (YAKUTIA): COMPOSITIONAL FEATURES AND 40AR/39AR DATING

D.V. Kuzmin 1*, A.A. Tomilenko 1, D.S. Yudin 1
Sobolev Institute of Geology and Mineralogy, SB RAS, Novosibirsk, Russia
Keywords: high-barium phlogopite, kimberlite, Malokuonapskaya pipe, 40Ar/39Ar age

Abstract >>

We present new data on high-barium phlogopites, first discovered in the kimberlite of the Malokuonapskaya pipe. The studied phlogopites can be divided into two groups: 1 – megacrysts up to 2 mm in size with a BaO content of up to 0.58 wt.%, characterized by an increase in the content of this component from the center to the edge (having direct zoning by BaO), and the 2nd group – zonal crystals up to 200 µm in size, containing minerals of the bulk mass of kimberlite, with a BaO concentration of up to 14.6 wt% in the central parts, regularly decreasing to 1 wt% towards the edges of the crystals. The formation of these two generations of micas corresponds to different, unrelated processes. Crystallization of megacrysts took place at the earliest stages of the evolution of the kimberlite melt. A slight increase in Ba concentration from the centers to the edges of phenocrysts may be a consequence of the evolution of kimberlite melt with its enrichment in incompatible elements. Phlogopites of the second group were formed at a later stage, together with the minerals of the groundmass. High barium contents in these phlogopites are possible with a light elements enrichment of the kimberlite melt. The source of these elements could have been the refertilized lithosphere under the influence of the Siberian traps.

40Ar/39Ar dating of phlogopite showed an age of 232.1+2.6 million years.



49.
KINETIC COEFFICIENTS MEASUREMENT UNDER POROUS LIQUID LATERAL OSCILLATIONS IN ELECTROMAGNETIC FIELD

V. N. Dorovsky, S. V. Dorovsky

«Siberian Software» Ltd, Novosibirsk,  Russia


Keywords: conductivity, acoustoelectric parameter, permeability, lateral oscillations, porous media, quasi-stationary electromagnetic field.
Abstract >>

Configuration of acoustic and magnetic fields, under which in borehole conditions lateral acoustic oscillations emerge in porous saturated medium, is examined. Alternating magnetic field under condition of electroacoustic conversion produces measurable acoustic response at the interface of two media. The character of dependency between amplitude of media interface surface oscillations and medium parameters is described. Possibility of simultaneous measurement of three kinetic coefficients (conductivity, acoustoelectric parameter, permeability) is demonstrated.



50.
A STUDY OF THE U IN SEDIMENT PHOSPHATE ASES

А.E. Boguslavsky1, 2, O.L. Gaskova1,3, S.M. Sofronova1, A.А. Saraev4, Z.S. Vinokurov5, A.V. Safonov6


1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia, 2 Novosibirsk State Technical University, Novosibirsk, Russia 3 Novosibirsk State University, Novosibirsk, Russia 4 Boreskov Institute of Catalysis, Novosibirsk, Russia 5 Synchrotron Radiation Facility SKIF, Boreskov Institute of Catalysis, Koltsovo, Russia 6 Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Moscow, Russia
Keywords: uranium adsorption, uranium oxides, groundwater purification, valent state.
Abstract >>

Since apatite is capable to adsorb and retain radionuclides, the removal of uranyl (UO22+) ions from two Ca-containing technogenic and model solutions (1-2 g/L of Ca) was studied when neutralized with sodium hydrogen phosphate solution Na2HPO4. Chemical composition of the sediments was analyzed by XPS and their structure was refined by XRD. The hydroxyapatite formation was confirmed using both XPS and XRD. XRD proves that the two samples contained additional CaH(PO4)•(H2O)2 (brushite), in which calcium changes to uranium of up to 15% in a model solution. When identifying the oxidation state of uranium, the presence of U4+, U5+ и U6+ was noticed with U5+ of up to 30-35 at% from the total amount.

SEM-EDS images of the sediment phases did not allow to determine location of the phases with an uranium content over 18%, for example Ca(UO2)2(PO4)2·11H2O (autunite) or other uranium phosphates. Uranium is detected at the grain rims, indicating a sorption nature of its accumulation. Thermodynamic computations showed the possible formation of independent uranium phases, such as ß-UO2.333, ß-UO2(OH)2 and NaUO2O(OH) (clarkeite), at the measured Eh-pH. The supersaturation of solutions and the spontaneous formation of hydroxyapatite and brushite solid particles lead to a change in the initial Ca/PO4 ratio, where the P/Ca and Ca/O ratios, as well as the elemental composition in the near-surface layer of three sediments, are not strictly constant. Newly formed phase contains isolations different in size, deformation degree, presence of sorption surface groups, which is reflected in the mechanism of uptake of uranium compounds. No similar study has been performed with uranium, and our results demonstrate the need for further studies on the influence of uranium on apatite crystallization. The stability of phosphate phases shows the high reliability of phosphate safety barriers for the uranium extraction facilities, and these processes can be used for remediation areas of aquifers contaminated with radionuclides



51.
UPPER VENDIAN NEMAKIT-DALDYNIAN STAGE IN THE SIBERIAN PLATFORM

V.V. Marusin




1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: Vendian, Cambrian, General Stratigraphic Scale of Russia, International Chronostratigraphic Chart, small skeletal fossils, trace fossils, chemostratigraphy, Siberian Platform
Abstract >>

A recent revision of stratigraphic volume and age of the Upper Vendian Nemakit-Daldynian Stage has developed its integrated (bio- and chemostratigraphic) characteristic. This unit comprises the strata between the first appearance of undisputed anabaritids in the fossil record (ca. 539 Ma) and first Tommotian small skeletal fossils of Nochoroicyathus sunnaginicus Assemblage Zone of the Lower Cambrian (ca. 530 Ma). Together with typical assemblages of skeletal fauna, the Nemakit-Daldynian Stage records specific changes in trace fossil assemblages and carbonate carbon isotope composition. Following the formulated criteria, this contribution tests how complete the geological record of the Nemakit-Daldynian Stage is in its reference sections (western Anabar Uplift) and other regions of the Siberian Platform (eastern Anabar Uplift, Olenek Uplift, Kharaulakh Uplift, Uchur-Maya region, Batom Basin, Baikal region, Irkutsk and Biryusa Cis-Sayans uplifts, southern and northern Yenisei Ridge, Turukhansk Uplift, Igarka Uplift, central Siberian Platform).



52.
CONDITIONS OF FORMATION, SEDIMENTATION CYCLICITY AND MODELS OF VOIDNESS OF FAMENNIAN DEPOSITS OF THE YUGOMASHEVSKOYE FIELD OF THE REPUBLIC OF BASHKORTOSTAN

A.S. Dushin, T.V. Burikova, D.S. Tarnovetsky

1Ufa State Petroleum Technological University, Ufa, Russia

2OOO RN-BashNIPIneft, Ufa, Russia


Keywords: carbonate structures, Famennian stage, facies, cyclicity, sedimentogenesis, secondary transformations, porosity, fracturing, leaching, Yugomashevskoye field
Abstract >>
The article summarizes new data on core and geophysical studies of wells of Famennian deposits in the Yugomashevskoe field located in the Republic of Bashkortostan (Russian Federation). Structurally, the object under consideration belongs to the model of a rimmeded platform with its characteristic elements—organogenic structures and associated facies. The identified sedimentation cyclicity and secondary processes, combined with an analysis of changes in relative sea level, made it possible to identify the most common types of porosity confined to one or another part of the section and facies zonation. Transgressive and regressive parts of the cycles are characterized by their specific set of lithotypes and characteristic types of void space. It was revealed that the formation of void space was influenced by the duration and intensity of secondary processes: leaching, dolomitization, claying associated with the removal of rocks to the surface. In addition, the work substantiates the division of carbonate structures of the study area into three types, differing in position, morphology, as well as in the different manifestations of hupergene transformations, which is reflected in the differentiation of the types of void space of the rocks compose them and their potential in terms of reservoir properties.



53.
CALCIFIED CYANOBACTERIA IN THE LATE MIDDLE ORDOVICIAN BIOHERMS AND PELECYPOD BANKS OF THE MOYERO RIVER SECTION (NORTHERN SIBERIAN PLATFORM)

N.A. Lykov1,2, Yu. V. Rostovtseva3, I.G. Zakiryanov4, A.V. Timokhin4, A.V. Dronov1, T.V. Gonta4, O.V. Postnikova2
1Geological Institute, Russian Academy of Sciences, Moscow, Russia 2Gubkin Russian State University of Oil and Gas, Moscow, Russia 3Geophysical Center of the Russian Academy of Sciences,Moscow, Russia 4Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: сalcified cyanobacteria, Ortonella, Garwoodia, Hedstroemia, bioherms, biostroms, pelecypod banks, Siberian platform, uppermost Middle Ordovician, сyanotoxins

Abstract >>
In the Middle Ordovician (Late Darrivillian) deposits (Kirensk-Kudrinian Regional Stage) of the Moyero River section (Tunguska syneclise, Eastern Siberia), the remains of calcareous cyanobacteria of the genera Garwoodia Wood, 1941, Ortonella Garwood, 1914, and Hedstroemia Rothpletz, 1913 (family Garwoodiaceae) were identified for the first time in thin sections. Previously, Ortonella and Garwoodia were recorded on the Siberian Platform only in Silurian deposits, which makes the discovery of representatives of these genera the earliest for that region. Ortonella (center part) and Garwoodia (uppermost part) dominate in stromatoporoid-cyanobacterial bioherms, while Hedstroemia occupies a subordinate position. Only Ortonella was found in the biostromes and shelly interlayers of pelecypod banks. The study of the lithology of Kirensk-Kudrinian deposits allowed us to reconstruct a shallow lagoonal type sedimentation environment for the studied part of the section. Under these conditions despite the global increase in biodiversity during the Great Ordovician Biodiversification Event (GOBE), skeletal metazoan organisms failed to become the main framework of biostromes and bioherms. Their role was taken over by cyanobacterial communities resistant to the conditions of extreme shallow-water carbonate-siliciclastic sedimentation regime with terrigenous domination. The growth and subsequent bloom of the latter apparently provoked an increase in phosphorus content in the bottom sediments, which probably caused a local paleoecological crisis of the benthic fauna by the end of the Kirenian time in this part of the paleobasin. This is also confirmed by the depleted ostracod complex in the Moyero River section (in contrast to the same-age deposits of the Lena, Podkamennaya Tunguska, and Kulymbe River sections). The decrease in biodiversity of benthic fauna and, in particular, of skeletal metazoan reef-builders during microbial ‘blooms’ can be explained by the impact of cyanotoxins, which are destructive to marine life. The research demonstrates that even in the epochs of global biota rise, local conditions could limit the participation of skeletal metazoan organisms in the formation of reef ecosystems, preserving the dominance of microbe communities. This emphasizes the role of microbial communities as key agents of carbonate sedimentation during transitional periods of palaeoecological rearrangements and changes in sedimentation type.



54.
FEATURES OF THE DEEP STRUCTURE OF THE UPPER CRUST AND MINERAGY IN THE SIKHOTE-ALIN FRAGMENT OF THE REFERENCE GEOLOGICAL-GEOPHYSICAL PROFILE 8-DV

V. M. Solovyev, A. S. Salnikov, V. S. Seleznev, T. V. Kashubina, N. A. Galyova, A.E. Shenmaier
1Altai‐Sayan Branch of Geophysical Survey of the Russian Academy of Sciences,Novosibirsk, Russia 2Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia 3Seismological Branch of Geophysical Survey of the Russian Academy of Sciences, Novosibirsk, Russia 4A.P. Karpinsky Russian Geological Research Institute, St. Petersburg, Russia


Keywords: deep seismic profile, longitudinal and transverse waves, P- and S-wave velocities and their ratios, deep seismic section, earth's crust, mineragenic zone
Abstract >>
The article presents the results of deep seismic studies based on P- and C-wave data on the 500-kilometer Sikhote-Alin fragment of the 8-DV reference geophysical profile. Deep seismic sections of the upper crust (to a depth of 15-20 km) with the distribution of longitudinal and shear wave velocities were constructed. The P-wave velocity over most of the Middle Amur Basin and the East Sikhote-Alin volcano-plutonic belt varies from 4-5 km/s in the uppermost part of the section to 5.8-6.3 km/s at depths of 7-15 km. The Sikhote-Alin orogenic belt in the section along the profile is represented by an anticlinal structure with high-velocity (up to 5.5-5.8 km/s) rocks uplifted in the central part; At great depths of 10-20 km within its limits, the P-wave velocity values were 6.1-6.3 km/s. In the upper part of the section, the S-wave velocity value within the profile as a whole is 2.7–2.9 km/s; reduced values (2.6–2.8 km/s) are observed in the central and eastern parts of the Middle Amur Depression and the eastern section of the East Sikhote-Alin volcano-plutonic belt, increased velocity values up to 3.35 km/s are observed in the central part of the Sikhote-Alin orogenic complex. At depths of 5–15 km within the section, the S-wave velocity increases to 3.4–3.65 km/s. The same behavior of the upper part of the earth's crust to a depth of 15–20 km was established by the values of P- and S-wave velocities, their ratio, and Poisson's ratio. The analysis of the relationship between the identified anomalies and the location of large mineragenic zones of the Amur region was carried out in the profile section. The previously established correspondences on the 2-DV, 3-DV, 1-SB and Vostochno-Stan fragment profile 8-DV on the confinement of ore deposit series to zones of low P- and S-Stan velocity ratios and Poisson's ratio in the upper part of the earth's crust were confirmed. The relationship between the identified surface seismic anomalies and deep (at depths of 5–20 km) roots (intermediate magmatic foci), which can be considered ore-supplying, was substantiated..



55.

Behavior of macrocomponents during the formation of zonal sulfide ore on the basis of the experiment on the directional crystallization of Cu-Fe-Ni-S melt

E.F. Sinyakova1, D.A. Ulybin1,2,3, K.A. Kokh1, I.A. Kuzmin1


1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences,

Novosibirsk, Russia

2Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia

3Novosibirsk State University, Novosibirsk, Russia


Keywords: Cu-Fe-Ni-S system, phase equilibrium, zonality, fractional crystallization
Abstract >>

The quasi-equilibrium directional crystallization method was used to model a new type of zoning in the Cu-Fe-Ni-S system. A melt with the following composition (in at.%) was crystallized: 14.00 Cu, 30.00 Fe, 4.00 Ni, 51.00 S, and 0.1 each of Pt, Pd, Ag, Au, As, Te, Bi, Pb, Se, and Sn. Optical and electron microscopy, micro-X-ray spectral analysis, differential thermal analysis, and powder diffraction methods were used to analyze the composition and structure of the ingot. Based on the results of measuring the average solid phase composition, the distribution curves of macrocomponents in the ingot in the interval g from 0 to 0.81 (g is the fraction of crystallized melt) were plotted. The change of melt composition and distribution coefficients between solid phases and melt in the process of directed crystallization was also calculated. The obtained sample consists of three primary zones: the monosulfide solid solution with a composition ranging from (Fe₀.₇₅Ni₀.₁₀Cu₀.₀₆)0.91S to (Fe₀.₆₉Ni₀.₁₅Cu₀.₀₉)0.93S (Mss) the Zone I, and two intermediate solid solutions: ~ (Fe₀.₅₇Ni₀.₀₃Cu₀.₄₅)1.05S (Iss1) the Zone II and (Fe₀.₄₆Ni₀.₀₆Cu₀.₅₂)1.05S (Iss2) the Zone III. The peritectic character of the crystallization of Iss1 and Iss2 from the melt was established. The trajectories of melt and solid phases composition and series of conodes are plotted for Mss and Iss1 on the phase diagram of Cu-Fe-Ni-S system. Secondary zonality is described by the following sequence of phases: Pyh 1C + Pyh 3C + Icb + Ccp / Ccp + Iss + Fe-Pn, Sug / Ccp + Ni-Pn +NiS+Bn (Pyh - hexagonal pyrrhotite, Icb - isocubanite, Ccp - chalcopyrite, Pn - pentlandite, Sgk - sugakiite, Bn - bornite) and belongs to the high-sulfur pyrrhotite+cubanite-chalcopyrite type of ore body zonation.



56.
NORTH AMERICAN-BERING PLATE BOUNDARY: NEW PALEOMAGNETIC DATA ON LATE CRETACEOUS VOLCANIC ROCKS OF CENTRAL CHUKOTKA

I.E. Lebedev1, V.E. Pavlov1, P.L. Tikhomirov1, A.M. Pasenko1, U.S. Efremova2


1Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
2Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: North-East of Eurasia, Bering Sea region, Okhotsk-Chukotka volcanic belt, Valunistoe deposit, paleomagnetism, geochronology.
Abstract >>
This paper presents new geochronological and paleomagnetic data that support the idea of later termination of magmatism in the Okhotsk-Chukotka Volcanic Belt (OCVB) within the East Chukotka flank zone than previously thought. It also allows the calculation of a new paleomagnetic pole (78.6°N, 212.2°E, A95= 4.7°, N=104) with an age of ~72 Ma for the vicinity of the Valunistoe deposit. Combined with paleomagnetic data previously obtained by us for the Kupol deposit area, the new results lead to the following conclusions: 1. The studied areas (the "Kupol" and "Valunistoe" location) have experienced relatively small, but statistically significant, displacements relative to the North American plate during the time interval from the Late Cretaceous to the present. 2. The "Kupol" location is rotated counterclockwise by several to a few tens of degrees relative to the North American plate, while the "Valunistoe" location is displaced relative to this plate in latitude by a distance of at least several hundred kilometers. 3. Based on the obtained data, we propose a model, building on the existing Bering Sea region model of Redfield and Fitzgerald (1993), according to which the "Kupol" and "Valunistoe" locations belong to the boundary area between the North American plate and the Bering plate, represented by a series of tectonic blocks. The tectonic block to which the "Valunistoe" location belongs is one of the westernmost blocks grouped into the Bering plate, while the "Kupol" location belongs to the easternmost regions of the Chukotka deformed margin of the North American plate. Deformations arising in the interaction of these tectonic blocks in the region under consideration are mainly diffuse. The Trans-Bering Seismic Belt appears to be a potential area where the discussed deformations may be most concentrated.



57.
STRUCTURAL AND COMPOSITION CHARACTERISTICS OF IMPACTITES OF COPTOMICT FACIES OF THE KARA ASTROBLEME RIM

N.I. Maksimenko1, T.G. Shumilova1
1N.P. Yushkin Institute of Geology, FRC Komi SC UB RAS, Syktyvkar, Russia
Keywords: Suevite, impactite, Kara astrobleme, impact facies, shock metamorphism, impactogenesis

Abstract >>

The impact facies are subdivided to coptogenic (primarily deposited) and coptomictic (redeposited) units. The redeposited impact facies remain poorly studied at present. In this work, the deposits of the coptomictic facies on the basis of the Kara astrobleme are characterized in detail for the first time. Structural and textural features of impactites at the macrolevel and microscopic structural and material features of the constituent components (lithoclasts, vitroclasts and matrix) of lapilli and agglomerate suevites of the Sayakha River area are considered. According to the reconstruction, the breccia impactites of the crater rim at the northwestern sector of the Kara astrobleme were formed under conditions of the landslides facies from the crater wall at the stage of early modification of the astrobleme. The results obtained can be used to reconstruct a model of the Kara impact structure formation and to improve the unified model of the breccia impactites formation of coptomictic facies in a large meteorite crater.



58.
EVALUATION OF STRESS-STRAIN STATE OF LITHOSPHERE IN RECTANGULAR AND CYLINDRICAL MODELS ALONG THE CRATON PROFILE

R.A Bakeev, Y.P. Stefanov, E.A. Melnik, V.D. Suvorov, A.A. Tataurova


Keywords: elastic-plastic deformation, numerical modeling, stress-strain state, seismic profile Craton, flat model, cylindrical model, spherical model, horizontal stresses, tangential stresses
Abstract >>
Within the framework of the elastic-plastic model of the behavior of the medium, the influence of the non-uniform distribution of properties and the geometry of the problem on the stress-strain state of a 500 km thick block model under the action of gravity is considered. Calculations were carried out in a 2D formulation of a plane stress state for a rectangular and cylindrical profile, taking into account the curvature of the Earth's surface. It is shown that anomalies in the stress-strain state and zones of development of irreversible deformation are determined primarily by the heterogeneity of the structure, the presence of density and rheological anomalies. The geometry of the models, taking into account the curvature of the lithosphere significantly affects primarily the stress state in the crust, where the greatest shear strength is, which determines the development of irreversible deformation depending on the heterogeneity of the medium.
In this work, to assess the influence of the geometric factor on the stress-strain state of the lithosphere, numerical modeling of its seismic model along the Craton profile, 3600 km long and 500 km deep, presented in rectangular and cylindrical coordinates, was carried out. A comparison of the obtained solutions was carried out.
The change in the stress-strain state during the rise and immersion of a block of the medium with a cylindrical formulation of the problem is considered. It is shown that vertical displacements with such a formulation have a noticeable effect on horizontal stresses and can lead to the development of irreversible deformation.
It is shown that with successive layer-by-layer build-up of the crust, the deviation of tangential stresses in a cylindrical setting from horizontal stresses of a flat model at the surface is negligibly small. The maximum deviation occurs at the middle of the depth of the deformed layer.




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