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2012 year, number 4

1.
GEOCHEMICAL FEATURES OF METABASITE INCLUSIONS IN GRAY GNEISSES OF THE BAIDARIK BLOCK ( Central Mongolia )

V.A. Belyaev, M.A. Gornova, A.Ya. Medvedev, and N.N. Pakhomova
A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Archean, metabasites, tonalite-trondhjemite-granodiorite, Baidarik block, Mongolia
Pages: 321-333

Abstract >>
The Baidarik block of the Dzavhan microcontinent (Central Asian Fold Belt) includes the Upper Archean Baidaragin gray-gneiss complex. Among gray plagiogneisses, there are metabasic bodies, which are probably relics of early volcanics. By composition, the metabasites are divided into three petrochemical groups, whose protoliths were tholeiitic basalts, Al-undepleted and Al-depleted basaltic komatiites. Only a few samples are similar in REE composition to these protoliths. We have found metabasites with crustal-contamination features. The unusual geochemical properties of the metabasites (LREE enrichment and Nb, Zr, and Ti depletion) are related to their metasomatism.



2.
PETROLOGICAL AND MINERALOGICAL FEATURES OF VOLCANIC ROCKS FROM THE CENTRAL KUZNETSK BASIN ( southern Siberia )

A.V. Nastavko, E.V. Borodina, and A.E. Izokh
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Petrology, mineralogy, geochemistry, andesitic basalts, trap, Permo-Triassic, Kuznetsk Basin
Pages: 334-346



3.
FORMATION OF GOLD-SILVER SULFIDES AND NATIVE GOLD IN THE SYSTEM Fe-Au-Ag-S

G.A. Pal'yanovaa, K.A. Kokha, and Yu.V. Seryotkina,b
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNovosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Fe-Au-Ag-S system, iron sulfide melt, pyrite, pyrrhotite, gold-silver sulfide melt, solid solutions Ag2-x AuxS, uytenbogaardtite, petrovskaite, high-fineness gold
Pages: 347-355



4.
OLIGOCENE DEPOSITS OF THE BAIKAL RIFT VALLEY

I.M. Mashchuk and N.I. Akulov
Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Sandstone, siltstone, coal, flora, palynology, stratigraphy, Tankhoi Formation, Baikal Rift, East Siberia
Pages: 356-366

Abstract >>
New data are reported on the stratigraphy of the Oligocene deposits of Lake Baikal (the Tankhoi field, the outcrops near the mouths of the Osinovka, Polovinka, and Klyuevka Rivers). Detailed paleontological analysis of the key sections on the continental part of the Baikal eastern coast revealed four floristic horizons that could be used as indicator horizons and showed that the Tankhoi Formation formed throughout the Oligocene and at the early Early Miocene. Lithologically, blue vivianite clays and coal beds could be used as the most important indicator horizons. Formation of the deposits began after a long stratigraphic break from the Early Cretaceous to the Early Oligocene. The deposits were formed by erosion and denudation of weathering crust and accumulation of redeposited weathering residues in the Tankhoi paleobasin with a lacustrine-marsh landscape. Coarse-clastic foehn deposits of the Osinovka Formation, containing rich Miocene palynological assemblages, were eroded and overlie concordantly the Upper Tankhoi Subformation and redeposited weathering residues of the weathering crust, and underlie the Anosovka Formation. The study suggests that the Baikal rift valley began to form at 38 Ma.



5.
COMPOSITIONAL, STRUCTURAL, AND GEODYNAMIC CONTROLS OF THE EVOLUTION OF INTER- AND INTRAMONTANE BASINS OF THE TIEN SHAN

V.I. Makarov†
Institute of Geoecology, Russian Academy of Sciences, Ulanskii per. 13, Moscow, 101000, Russia
Keywords: Intracontinental mountain building, recent geodynamics, foreland basins, intermontane and intramontane basins, Tien Shan
Pages: 367-375

Abstract >>
The crustal orogeny which formed the present-day Tien Shan results from the complex interaction between two independent processes. The first is the lateral (horizontal) compression related to the collision between the Indian and Eurasian Plates. The second is the rearrangement and flow of crustal material at different levels of the lithosphere beneath the mountain belt. Two broad morphologic and genetic types of mountain basins (intramontane and intermontane/foreland) are proposed as indicators of specific geodynamic factors controlling the topographic relief of the orogenic belt. The first-type basins, having the upper crustal roots, reflect mainly the N-S crustal compression and correspond to simple (elementary) longitudinal folds with basement involvement. The second-type basins developed mostly in response to deep processes in the upper mantle and lower crust.



6.
PLATE BOUNDARIES IN THE FAR EAST REGION OF RUSSIA ( from GPS measurement, seismic-prospecting, and seismological data )

V.Yu. Timofeeva, D.G. Ardyukova, V.M. Solov'evb, S.V. Shibaevc, A.F. Petrovc, P.Yu. Gornovd, N.V. Shestakove,f, E.V. Boikoa, and A.V. Timofeeva
aA.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bGeophysical Survey, Siberian Branch of Russian Academy of Sciences, pr. Koptyuga 3, Novosibirsk, 630090, Russia
cYakutian Department of the SB RAS Geophysical Survey, pr. Lenina 39, Yakutsk, 677980, Russia
dYu.A. Kosygin Institute of Tectonics and Geophysics, Far Eastern Branch of Russian Academy of Sciences, ul. Kim Yu Chena 65, Khabarovsk, 680000, Russia
eFar Eastern Federal University, ul. Sukhanova 8, Vladivostok, 690950, Russia
fInstitute of Applied Mathematics, Far Eastern Branch of Russian Academy of Sciences, ul. Radio 7, Vladivostok, 690041, Russia
Keywords: Tectonic plates; plate boundaries; space geodesy method; seismological and seismic methods for investigating the deep structure of the Earth's crust
Pages: 376-391

Abstract >>
The recent geodynamics of the Far East region of Russia is considered, where three large tectonic plates converge - Eurasian, North American, and Pacific, as well as several microplates-Okhotsk, Bering, and Amurian - have been hypothesized to exist. The available data on the position of the plate boundaries, the relative plate rotation poles, and the regional seismicity were analyzed, and parameters of plate motion models for northeastern Russia were determined in this study. The regional deep structure was investigated, using data obtained by different geophysical methods. The results of observations of the Magadan-Vrangel Island profile by deep seismic sounding (DSS), common-depth point (CDP) method, and correlation refraction method (CRM) are presented.



7.
A TECTONOPHYSICAL MODEL OF THE BAIKAL SEISMIC ZONE: TESTING AND IMPLICATIONS FOR MEDIUM-TERM EARTHQUAKE PREDICTION

S.I. Sherman, S.V. Lysak , and E.A. Gorbunova
Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Seismicity, seismic zone, tectonophysical model, active faults, lithospheric deformation zone, strain waves, earthquakes, earthquake prediction, Baikal seismic zone
Pages: 392-405

Abstract >>
The first tectonophysical model of the Baikal seismic zone represents a separate complex region of the lithosphere. It has a pinnate structure with a backbone belt of current deformation, which is a concentrator of largest earthquakes, and branching, repeatedly reactivated large and small faults. In its vertical section, the seismic zone is tree-like, the stem and the branches being faults of different size ranks which can generate earthquakes when reactivated. The real-time short-period fault motions and the respective seismicity occurring at a certain time and in certain places are triggered by strain waves, which disturb the metastable state of the faulted lithosphere subject to regional stress. The modeling work includes developing general requirements for tectonophysical models of continental rifts and special methods for identifying the faults that become active within short historic time spans, as well as techniques for locating potential events in space and time in specific active faults. The methods and model testing for medium-term earthquake prediction are described by the example of the well-documented Baikal seismic zone, which is the most active part of the Baikal rift system. The tectonophysical model for the Baikal zone is statistically supported by field data, and this allows estimating the velocities and periods of strain waves for different zone segments and faults, with implications for nearest-future earthquake prediction.



8.
FAST-DECAYING INDUCTIVE IP IN FROZEN GROUND

N.O. Kozhevnikov
A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: TEM surveys, induced polarization, frozen ground, ice, low-frequency dielectric permittivity, Maxwell-Wagner effect, electrochemical polarization, surface conductance
Pages: 406-415

Abstract >>
Effects of induced polarization (IP) often appear in TEM data collected in Yakutia and elsewhere in permafrost areas. Inversion of transient responses using the Cole-Cole model of frequency-dependent conductivity shows fast decaying induced polarization in the shallow subsurface (within 100 m). Frozen ground within these depths has the chargeability ( m ) in the range from 0.2 to 0.85 (mostly 0.2-0.5); the relaxation time constant (τ) varies from 35 to 250 ?s, being 50-100 ?s on average, and the exponent c is little variable, unlike m and τ (from 0.8 to 1). The latter fact ( c ≈ 1) is indicative of a narrow range of relaxation times fitting the Debye relaxation model. Conversion of the complex conductivity into relative low-frequency dielectric permittivity results in values of the order of tens of thousands or a few hundred thousand. These exceptionally high permittivities have no other plausible explanations than electrochemical polarization of unfrozen water that remains bound on the surface of mineral grains at subzero temperatures. The effects of electrochemical polarization are described and interpreted in terms of frequency-dependent surface conductivity, which is controlled by surface-to-volume ratio.



9.
CRUSTAL GEODYNAMIC ACTIVITY: MANIFESTATIONS IN CLOUD FIELDS

L.I. Morozova
Institute for Complex Analysis of Regional Problems, Far Eastern Branch of the Russian Academy of Sciences, ul. Sholom-Aleikhema 4, Birobidzhan, 679016, Russia
Keywords: Lithoatmospheric coupling, linear cloud anomalies, satellite image, geodynamic monitoring
Pages: 416-423

Abstract >>
We consider different kinds of linear cloud anomalies appearing in satellite images over activated crustal faults. The spatiotemporal relationship between earthquakes and cloud anomalies was studied by statistical methods. It has been shown that these cloud anomalies in the atmosphere can be used for short-term prediction of the earthquake time and region. Also, we consider the earthquake-related evolution of the giant thunderstorm cloud near the epicenter before the earthquake.