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Russian Geology and Geophysics

2018 year, number 9

1.
PERMO-TRIASSIC STAGE OF ALKALINE MAGMATISM IN THE VITIM PLATEAU (western Transbaikalia)

A.G. Doroshkevich1,2, I.A. Izbrodin1, M.O. Rampilov1, G.S. Ripp1, E.I. Lastochkin1, V.B. Khubanov1
1Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakhyanovoi 6a, Ulan Ude, 670047, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Alkali and nepheline syenites, Permo-Triassic stage of magmatism, geochronological and isotope data, albitization, sources of material

Abstract >>
We present results of geochronological (40Ar-39Ar, U-Pb SHRIMP-II, and LA-ICP-MS) and geochemical studies of alkaline rocks of the Amalat, Sirikta, Tsipa, Pravyi Uligli, and Verkhnii Uligli massifs in the Vitim plateau (western Transbaikalia). The formation of the alkaline rocks and the accompanying albitization are dated at 261-242 Ma. The isotope inhomogeneity (εNd( T ) = +8.4 to -1.7) of the alkaline rocks indicates the heterogeneous composition of the source of their material having a depleted component, an enriched juvenile metasomatic fluid, and a crustal substrate.



2.
GEOLOGIC STRUCTURE OF THE MUKODEK GOLD FIELD (northern Transbaikalia) AND SOURCES OF MAtter (Pb-Pb and Sm-Nd data)

V.A. Vanin1, A.V. Chugaev2, E.I. Demonterova1, D.P. Gladkochub1, A.M. Mazukabzov1
1Institute of the Earths Crust, Siberina Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, Zh-17, 119017, Russia
Keywords: Gold mineralization, Mukodek gold field, gold-bearing metasomatites, Sm-Nd and Pb-Pb isotope data, northern Transbaikalia, Baikal-Muya belt

Abstract >>
The Mukodek gold field is located in the Yana zone of the Baikal-Muya fold belt (northern Transbaikalia). Its orebodies are gold-bearing metasomatites confined to the fault of NE strike. It is shown that pre-ore faults played a crucial role in the spatial localization of the orebodies, as they favored the concentration of ore-bearing fluids. Results of geological and structural studies, along with available geochronological data (40Ar-39Ar dates for micas in gold-bearing pyrite), testify to ore-forming processes in the ore field during two Late Paleozoic stages. Early gold-bearing metasomatites of sericite-chlorite-albite-ankerite-quartz composition formed at 320 Ma, and late gold-bearing vein metasomatites of ankerite(calcite)-quartz composition originated at 285 Ma. A Pb-Pb isotope study of gold mineralization has shown that ore lead was supplied into the mineral-forming system mainly from a mantle source, most likely, regional Neoproterozoic igneous rocks. According to Sm-Nd isotope data, these rocks formed with the participation of a material of mantle genesis.



3.
HIGH-K BASALTIC TRACHYANDESITE XENOLITHS IN PYROCLASTIC DEPOSITS FROM THE BEZYMIANNY VOLCANO (Kamchatka)

V.O. Davydova1, P.Yu. Plechov1,2, V.D. Shcherbakov1, A.B. Perepelov3
1Lomonosov Moscow State University, Leninskie Gory 1, Moscow, 119991, Russia
2Fersman Mineralogical Museum, Russian Academy of Sciences, Leninsky pr.18, korp. 2, Moscow, 119071, Russia
3A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, 664033, Irkutsk, Russia
Keywords: High-K basaltic trachyandesite, xenoliths, Bezymianny Volcano, Tolbachik Volcano

Abstract >>
Bezymianny is an active andesitic volcano of the Klyuchevskaya group, and its eruptive products are xenolith- and enclave-bearing basaltic andesites and dacites. Here we report the first occurrence of clinopyroxene-plagioclase high-potassium basaltic trachyandesite xenoliths (51.84-53.00 wt.% SiO2, 0.95-1.95 wt.% K2O) crystallized in the temperature range 1120-840 C in products of modern eruptions (2007, 2011, 2012). Basaltic trachyandesite differ systematically in petrologic and geochemical characteristics from all previously studied rocks from the Bezymianny Volcano. They correspond to the clinopyroxene-plagioclase porphyry rocks from the foot of the Tolbachik volcanoes.



4.
FAULTS IN THE BAIKAL REGION: MORPHOSTRUCTURAL AND STRUCTURE-GENETIC FEATURES (case study of the Buguldeika fault junction)

A.V. Cheremnykh, A.S. Cheremnykh, A.A. Bobrov
Institute of the Earths Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Faulted crust, neotectonics, lineaments, fault zone, standard fracture pattern

Abstract >>
Lineament analysis is applied to map the pattern of the Obruchev fault system in the Buguldeika Village area, where several fault zones (Olkhon, Primorye, Prikhrebtovyi, Buguldeika, and Kurtun) make up a junction. As inferred from the predominant directions of genetically related lineaments, the Olkhon, Primorye, and Prikhrebtovyi faults originated under NW-SE extension and compression. The extension and compression settings within these zones are reconstructed by analysis of lineaments that have prominent and poor geomorphic expression, respectively. However, the pattern of lineaments well expressed in the surface topography within a weakly deformed block corresponds to reverse slip, while that of poorly pronounced lineaments corresponds to left-lateral strike slip. The study confirms the idea that the latest extension (rifting) stage in the Baikal region reactivated fault zones but did not deform blocks. The blocks store record of residual deformation produced by previous settings of regional compression and shear. The obtained results agree with earlier tectonophysical analysis of faults and fractures in the area and prove the applicability of the suggested approach to map the fault patterns and reconstruct their respective stress settings in areas that underwent multiple deformation events of different ages.



5.
PROGLACIAL DAMLAKES IN EASTERN TRANSBAIKALIA: NEW INSIGHT INTO THE PLEISTOCENE PALEOGEOGRAPHY

F.I. Enikeev
Institute of Natural Resources, Ecology, and Cryology, Siberian Branch of the Russian Academy of Sciences, ul. Nedorezova 16a, Chita, 672014, Russia
Keywords: Glacial lakes, ice dam, paleogeography, Pleistocene, eastern Transbaikalia

Abstract >>
Paleogeographic reconstructions for the Samarovo, Taz, Murukta, and Sartan glaciations reveal the formation conditions of proglacial lakes dammed by ice in intermontane depressions and valleys of large rivers in eastern Transbaikalia. Middle-Late Pleistocene climate change is reconstructed using spore-pollen spectra from Pleistocene sediments in northern Transbaikalia. The age and lifetime of proglacial lakes are constrained by radiocarbon, thermoluminescence, and varve chronology of their bottom sediments in the periglacial zone. The lake levels remain recorded in sediments produced by deposition and erosion along the former lake shores, as well as in morphology and lithology variations of terminal moraines. A large proglacial lake, with a maximum level of 1020 m, occupied vast areas in Transbaikalia and its surroundings during the Samarovo glaciation. After the glaciers degraded, the Amur River system expanded into the area of closed lake basins in the southeastern Baikal region, including North China and Mongolia. The obtained results have implications for the Middle-Late Pleistocene history of lake deposition.



6.
INTERSTRATIFIED ILLITE-SMECTITE PHASES: FORMATION MECHANISMS AND PRACTICAL APPLICATIONS

G.A. Krinari, M.G. Khramchenkov
Kazan Federal University, Institute of Geology and Petroleum Technologies, ul. Kremlevskaya 4/5, Kazan, 420008, Russia
Keywords: XRD analysis, structure, interstratified illite-smectite phases

Abstract >>
Secondary micas after smectite, including mix illite-smectite phases, can form in sediments by three mechanisms, each being specific to particular environments. As the process develops, the newly formed phases undergo structure ordering. Two mechanisms involve transformation of 2:1 mixed-layer structures, and the third is the growth of screw dislocations, with formation of ordered mix phases having a Reichweite parameter of R = 1 or R = 2. We propose methods for identifying such phases when they are present in small amounts or when their XRD patterns lack well-pronounced superperiodic reflections, as well as mathematical formalism for illitization modeling. The theoretical issues are illustrated with field examples, and the illitization mechanisms are discussed in terms of their possible practical applications.



7.
A GENERALIZED IMAGE AND BOUNDARIES OF THE BAZHENOV FORMATION: CONSTRAINTS FROM WELL LOG DATA FOR SALYM-TYPE SECTIONS (West Siberia)

V.V. Lapkovsky1,2, V.A. Kontorovich1,2, N.E. Shmelev1,2
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Bazhenov Formation, Salym area, Zhekovsky plot, automated well correlation, Galtons composite portraiture, generalized image, average well

Abstract >>
A technique akin to Galtons composite portraiture is suggested for creating a generalized image of a stratigraphic unit based on well log data from a group of well sections. The procedure begins with superimposing stratigraphically equivalent section points according to pairwise correlation models followed by weighted summation of similar logs. The superimposition highlights persistent common features of the sections while their minor individual details become suppressed. A generalized model of the Bazhenov Formation in the Salym area has been constructed from gamma-ray, apparent resistivity, and self-potential logs. Radioactivity and resistivity anomalies, which are often used as constraints on the Bazhenov Formation boundaries, show a significant spatial discrepancy. According to the correlation, the formation volume in each well depends on the depth interval corresponding to the hypostratotype. The results were used to map the Bazhenov Formation thickness and its standard deviation, as well as average values of different logs.



8.
IDENTIFICATION OF THE GENETIC HETEROGENEITY OF TATARSTAN OILS BASED ON THE COMPOSITION OF ALKYL-SUBSTITUTED AROMATIC COMPOUNDS

M.B. Smirnov1, N.P. Fadeeva2, E.N. Poludetkina2
1A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow, 119991, Russia
2Moscow State University, Geological Department, Leninskie Gory 1, Moscow, 119991, Russia
Keywords: Tatarstan oils, alkylbenzenes, alkylnaphthalenes, genetic typification of oils

Abstract >>
This study presents data on concentrations of n -alkylbenzenes, n -alkylnaphthalenes, phytanylnaphthalene, and methylphytanylnaphthalene in representative crude oils of Tatarstan. The results of the study reveal the elevated concentrations of C19, C21, and C23 homologues of n -alkylbenzenes and n -alkylnaphthalenes, which can be considered biomarkers. The proposed procedure for comprehensive quantification of this group of biomarkers can be used as an efficient tool to study oils from the major petroleum basins of Russia. Based on the results of the study, four genetic groups of oils in Tatarstan have been distinguished: (1) oils from the north and northwest (Bir saddle, Lower Kama system of linear faults, and Saraily saddle), (2) oils from Devonian terrigenous reservoirs within the South Tatar arch and Melekes depression, (3) oils from Carboniferous reservoirs, and (4) oils from Devonian carbonate reservoirs. All these oils belong to the same genetic macrotype. Based on the results of this study, the sedimentary sections of the Melekes depression cannot be regarded as potential source rocks. It is assumed that oil has migrated to the northern part of the region from the north or east. Some of the possible migration routes for oils from the remaining part of Tatarstan are from the southeast and/or south.



9.
MIDDLE PALEOZOIC IMPACT EVENT IN THE SOUTHWEST OF THE EAST EUROPEAN PLATFORM

R.Kh. Sungatullin1, A.I. Bakhtin1, V.A. Tselmovich2, V.G. Bakhmutov3, G.M. Sungatullina1
1Kazan Federal University, ul. Kremlevskaya 18, Kazan, 420008, Russia
2Borok Geophysical Observatory of the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Borok Village 142, Yaroslavl, Region, 152742, Russia
3S.I. Subbotin Institute of Geophysics, National Academy of Sciences of Ukraine, pr. Palladina 32, Kyiv, 03680, Ukraine
Keywords: Lochkovian, impact explosion, differentiation processes, metallic microparticles, chemical composition, East European Platform

Abstract >>
A zone with high remanent magnetization and magnetic susceptibility has been identified at the boundary between Lower Devonian gray- and red-colored deposits in the southwest of Ukraine (in the southwest of the East European Platform). The microparticles of native iron and nickel and iron-nickel intermetallic compounds found here might be markers of an impact event in the Lochkovian (~415 Ma). Electron microscope examination and probe microanalysis of the chemical composition, morphology, structures, and textures of specific microobjects showed that they are the product of melting of meteoritic substance and target rocks caused by an impact explosion. Explosive dispersion and deposition of microparticles on the Earths surface result in a rapid differentiation of their substance. The obtained data can be used as evidence of a reference impact event during the fall of an iron-stone meteorite, and a characteristic set of minerals and geochemical parameters can help to identify catastrophic events in the geologic history.



10.
PALEOMAGNETISM OF TRAPS OF THE FRANZ JOSEF LAND ARCHIPELAGO

V.V. Abashev1,2, D.V. Metelkin2,1, N.E. Mikhaltsov1,2, V.A. Vernikovsky1,2, V.Yu. Bragin1,2
1A. A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: , Paleomagnetism, Large Igneous Provinces, FJL Archipelago, Arctic

Abstract >>
The paper presents results of paleomagnetic studies of traps of the Franz Josef Land (FJL) Archipelago. This area is considered to be part of the Barents Sea Large Igneous Province (LIP) and is usually associated with the Early Cretaceous stage of plume activity, by analogy with other manifestations of late Mesozoic trap magmatism in the High Arctic. Recent isotope-geochemical studies, however, suggest a much longer history of basaltoid magmatism in the FJL area, from Early Jurassic through Early Cretaceous, with three pulses at 190, 155, and ~125 Ma. Given a significant difference in age, paleomagnetic directions and corresponding virtual geomagnetic poles are supposed to form discrete groups near the Jurassic-Early Cretaceous paleomagnetic poles of Eastern Europe. However, the calculated virtual geomagnetic poles, on the contrary, show a single cloud distribution, with its center being shifted to the Early Cretaceous paleomagnetic poles of Siberia. The performed analysis demonstrates that the significant variance is caused mostly by the high-latitude position of the FJL and secular variations of the geomagnetic field during the formation of the traps. Products of the Early Cretaceous magmatism evidently prevail in the data sample. The coincidence of the average paleomagnetic pole of the FJL traps with the Early Cretaceous (145-125 Ma) interval of the apparent polar wander path of Siberia rather than Eastern Europe confirms the hypothesis of the Mesozoic strike-slip activity within the Eurasian continent. This activity might be a natural result of the evolution of the Arctic Ocean.



11.
FORMATION OF METHANE CONCENTRATION AND ELECTROMAGNETIC-FIELD ANOMALIES IN SOUTHWESTERN PETER THE GREAT GULF (Sea of Japan)

B.A. Burov, A.I. Obzhirov, A.I. Gresov, A.S. Salomatin, E.V. Maltseva, Yu. A. Telegin, I.G. Yugai, A.V. Yatsuk
V.V. Ilichev Pacific Oceanological Institute, Far Eastern Branch of the Russian Academy of Sciences, ul. Baltiiskaya 43, Vladivostok, 690041, Russia
Keywords: Free methane in the pore space of bottom sediments, methane seep, electrical conductivity of bottom sediments, Schumanns resonances in the Earths natural electric field

Abstract >>
We report methane concentrations in the bottom water layer and the upper layer of bottom sediments and the results of acoustic explorations of methane seeps on the shelf bordering the continental slope of the Sea of Japan region, in which electromagnetic Schumanns resonance oscillations were earlier recorded at continental-slope water depths of 500, 1000, and 2000 m. The occurrence of Schumanns resonances at such great depths is explained by an increase (a factor of more than 25) in the electrical resistivity of a ~2000 m thick sediment layer with the pore space largely filled with free methane. A new method is proposed for determining the depth of the sources of anomalous concentrations of methane in bottom sediments or in the bottom water layer on a deep shelf. The method is based on recording Schumanns resonances during measurements of the natural electric field at a series of increasing depths in areas bordering the continental slope.



12.
MATHEMATICAL AND PHYSICAL MODELING To Justify A NEW GEOPHYSICAL METHOD - ELECTRICAL ANISOTROPY LOGGING

A.D. Karinskiy1, A.A. Krasnoselskikh2
1Sergo Ordzhonikidze Russian State Geological Prospecting University, ul. Miklukho-Maklaya 23, Moscow, 117997, Russia
2Central Research Institute of Geological Prospecting for Base and Precious Metals, Varshavskoe Shosse 129, korp. 1, Moscow, 117545, Russia
Keywords: Electromagnetic logging, electrical-anisotropy coefficient, mathematical modeling, physical modeling

Abstract >>
Results of theoretical and experimental studies obtained for an electromagnetic logging probe of new design are presented. As in the case of an induction logging probe, the magnetic dipole of the new probe produces a harmonically varying electromagnetic field, and the parameter to be measured is the electric voltage in the short receiving MN line. The theoretical studies have shown that under certain conditions, the results of measurement with this probe depend on the electrical-anisotropy coefficient and do not depend on the longitudinal and transverse electrical resistivities of the anisotropic medium. A technique for determining the electrical-anisotropy coefficient was tested on the experimental data obtained by physical modeling.