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Russian Geology and Geophysics

2017 year, number 7

1.
NEOTECTONICS OF EASTERN GORNY ALTAI: EVIDENCE FROM MAGNETOTELLURIC DATA

I.S. Novikov1, E.V. Pospeeva2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Magnetotelluric soundings, neotectonics, Gorny Altai

Abstract >>
According to 2D magnetotelluric (MT) data from northeastern and southeastern Altai, numerous neotectonic faults cut the Gorny Altai territory as a whole, as well as large basins within its limits, into blocks. Large neotectonic faults are traceable depthward in MT-based cross sections as zones of very low resistivities (below 0.5 Ohmm). The MT data generally confirm the fault geometry inferred previously from morphotectonic and geological evidence. Fault plane dips are vertical in normal and strike-slip faults and inclined in reverse faults. The nearly vertical and dipping zones of neotectonic faults crosscut a horizontal conductivity anomaly at depths of 10-15 km. The anomaly makes a natural divide between the zones of brittle crustal failure above and ductile downward pressing of material below. It may be responsible for the high tectonic and seismic activity potential of the upper lithosphere in Gorny Altai associated with growth of mountains and crust thickening. Beneath the Chuya and Kurai large basins, the conductivity anomaly occurs at a shallow depth of 10 km and has a resistivity below 10 Ohmm.



2.
MORPHOTECTONIC INVERSION IN THE TUNKA RIFT BASIN (southwestern Baikal region)

A.A. Shchetnikov1,2
1Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Basin inversion, inversion uplift, Cenozoic rifting, Baikal rift system, Tunka rift

Abstract >>
The general basement subsidence trend in the Tunka rift is locally interrupted by uplift (basin inversion). The inversion uplift causes deformation to basin sediments and shows up in the surface topography as morphostructures of two types. Inversion in the area is either part of rifting, when the subsidence-to-uplift change is driven by the rifting mechanism, or perturbs the rifting trend as superposed Gobi-type mountain growth, but is never associated with change from continental rifting to other tectonic setting. The presence of buried erosion cutouts in the rift valley floor indicates that wave-like vertical motions, with erosion during uplift and deposition in the erosion cutouts during subsidence, superpose on differentiated (orogenic) motions. The latest phase of basin inversion acted in the Tunka rift in the second half of the Late Pleistocene-Holocene, and the amount of uplift varied from a few tens to a few hundreds of meters. The highest 300 m uplift was in the Tor rift basin, as estimated from relative elevation of its ~55 ka sediments. In general, inversion uplift occurred over 40 % of the Tunka basin area (872 km2 of 2240 km2), and about 450 km2 of this uplift (49 % of the uplifted area or 20 % of the rift valley floor) grew by the Gobi-type mechanism. Quaternary sediments lie with a hiatus upon the Neogene strata in almost all sedimentary sections of basin margins, thus indicating that the deposition area reduced for a long period in the rift history and reached the former extent only in the earliest Late Pleistocene.



3.
A CONTINUUM MODEL OF PRESENT-DAY CRUSTAL DEFORMATION IN THE PAMIR-TIEN SHAN REGION CONSTRAINED BY GPS DATA

A.N. Mansurov
Research Station, Russian Academy of Sciences, Bishkek, 720049, Kyrgyzstan
Keywords: Deformation, tensor, crust, GPS velocities, 2D/3D model, weighted least-squares method, software

Abstract >>
We present a new model of crustal deformation in the Pamir-Tien Shan region. There are two different ways of assessing the deformation: block and continuum modeling. In this study we adopt a continuum modeling approach, which is based on computation of the two-dimensional strain rate tensor field of the Earths crust. This approach allows independent computation of the deformation at any point of the computation grid by solving an over-constrained system of linear algebraic equations based on the linear term of the Taylor series expansion of any geoenvironment point velocity function about its radius-vector. We propose a detailed description of this method including a significance criterion introduced by the author for estimating the reliability of modeling results. We discuss the parameters of this deformation model for the Pamir-Tien Shan region, computed from the GPS velocity data measured at 506 sites of the Central Asian GPS network. The most distinctive features of the estimated strain field are N-S shortening of the largest basins in the Tien Shan and at the junction between the Pamir and Tien Shan, as well as the westward motion of the eastern and western boundaries of the Pamir relative to the Tarim plate and Tajik depression.



4.
CONDITIONS OF FORMATION OF GOLD-BEARING MAGNETITE-CHLORITE-CARBONATE ROCKS OF THE KARABASH ULTRAMAFIC MASSIF (South Urals)

V.V. Murzin1, D.A. Varlamov2, G.A. Palyanova3,4
1Zavaritsky Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences, ul. Akademika Vonsovskogo 15, Yekaterinburg, 620016, Russia
2Institute of Experimental Mineralogy, Russian Academy of Sciences, ul. Akademika Osip'yana 4, Chernogolovka, 142432, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
4Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Magnetite-chlorite-carbonate rocks, chloritolites, rodingites, gold-rare-metal-REE mineralization

Abstract >>
Ilmenite, apatite, monazite, aeshynite-(Y), zircon, baddeleyite, thorianite, uraninite, and copper-containing native gold have been revealed in specific magnetite-chlorite-carbonate rocks and chloritolites in the Karabash ultrabasic massif in the South Urals. Dolomite from the magnetite-chlorite-carbonate rocks are characterized by a rather uniform isotope composition (δ13 = -0.9 to -1.9, δ18 = 11.5-13.6, 87Sr/86Sr = 0.70422-0.70469) corresponding to a mixture of sources: marine limestones and mantle fluids. We determined the isotope compositions of antigorite from serpentinites (δD = -79.1 and -89.6, δ18O = 7.4 and 7.6), of chlorite from chloritolites (δD = -57.8, δ18O = 7.8), and of magnetite-chlorite-carbonate rocks (δD = -59.2 and -69.6, δ18O = 6.4 and 5.9). The latter probably formed by the mechanism of filling of the free space at 480-280 ºC, and chloritolites were developed after serpentinites. Oceanic serpentinites, gabbros, limestones, and mantle fluids can be considered the source of material during the formation of magnetite-chlorite-carbonate rocks. A comparative analysis of the latter and the massif rodingites (chlograpites) bearing copper-containing gold was carried out. The established common features of these types of rocks are the localization in zones of tectonic melange, the presence of chloritolite rims, geochemical specialization, thermal conditions of formation, and isotope parameters of minerals and fluids.



5.
GEOELECTROCHEMICAL DETECTION OF PGE CONTENT ANOMALIES WITHIN THE SVETLYI BOR MASSIF (Central Urals)

O.F. Putikov1, N.P. Senchina1, I.V. Talovina1, A.M. Duryagina1, Yu.M. Telegin2, V.S. Nikiforova1
1Saint Petersburg Mining University, 21-ya liniya 2, St. Petersburg, 199106, Russia
2Ural MPG Joint-Stock Company, ul. Vostochnaya 56, Yekaterinburg, 620075, Russia
Keywords: Geoelectrochemistry, TMGM, Svetlyi Bor massif, platinum group elements (PGE)

Abstract >>
Experimental and methodological works were carried out by the thermomagnetic geochemical method (TMGM), one of geoelectrochemical methods, within the Svetlyi Bor platiniferous massif (Central Urals). We have analyzed the results of observation along two (search and test) profiles. The known distribution of platinum contents along the ditch in the test profile confirmed the effectiveness of the used method and made it possible to recognize the best indicators of platinum from the geoelectrochemical research data. The obtained results helped to reveal PGE-promising areas and suggested the presence of deep-seated blind orebodies.



6.
ADVANCEMENT OF MINERAGENIC REGIONALIZATION OF EASTERN TRANSBAIKALIA BASED ON GEOPHYSICAL STUDIES

V.G. Khomich1,2, N.G. Boriskina1,2
1Far East Geological Institute, Far East Branch of Russian Academy of Sciences, pr. 100 let Vladivostoku 159, Vladivostok, 690022, Russia
2School of Engineering, Far Eastern Federal University, ul. Suhanova 8, Vladivostok, 690950, Russia
Keywords: Regional metallogeny, large ore nodes, deep geodynamics

Abstract >>
Several metallogenic belts were earlier recognized by S.S. Smirnov in Transbaikalia rich in polymetallic endogenous mineralization. Despite the continuing geological and geophysical studies in the region, the borders of these belts are still hotly debatable. The results of geophysical and seismic tomographic studies in East Asia (where a stagnant oceanic slab was discovered in the mantle transition zone) and the location of highly productive ore-magmatic systems in the regional Earths crust testify to the spatial coincidence of the projection of the frontal part of the slab and the Dalainor-Gazimur-Olekma mineragenic zone. Most of large and superlarge ore nodes and fields with Au, Mo, U, Pb-Zn, Cu, and fluorite mineralization are localized in this zone. The difficult problem of mineragenic regionalization here can be solved by proving the probable influence of mantle fluid flows formed near the frontal part of the slab on the formation of highly productive ore-magmatic systems of the above zone oriented orthogonally to the earlier recognized belts. The experience gained during the comprehensive studies of minerageny not only in eastern Transbaikalia but also in other ore-bearing provinces can be used to choose ore-promising areas for prediction, prospecting, and assessment works.



7.
DIELECTRIC AND RADIO EMISSION PARAMETERS OF FORMATION AND CONDENSATE WATERS FROM GAS WELLS

M.I. Epov1,2, S.N. Menshikov3, A.N. Kharitonov3, A.N. Romanov4, V.S. Permyakov3, S.B. Bortnikova1, N.V. Yurkevich1
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
3Gazprom Dobycha Nadym, ul. Pionerskaya 7, Nadym, 656038, Russia
4Institute of Water and Environmental Problems, Siberian Branch of the Russian Academy of Sciences, Altai Krai, Barnaul, Molodezhnaya street, 1, Russia
Keywords: Formation, process, and condensate waters, complex dielectric constant, chemical composition, emissivity, microwave range

Abstract >>
A comprehensive study of water samples from the Medvezhe, Yubileinoe, and Yamsoveiskoe oil-gas condensate fields was performed for the rapid identification of liquids from gas wells. The proportions of condensate, formation, and process waters in the produced mixture are assumed on the basis of their physicochemical parameters and chemical composition. Their dielectric parameters were studied at a frequency of 0.6 GHz. Dependences of the dielectric and radio emission parameters on the total salinity and concentrations of major cations have been established. Algorithms for identifying different types of well water based on their dielectric parameters are proposed.



8.
DETERMINATION OF CORNER FREQUENCIES OF SOURCE SPECTRA FOR SUBDUCTION EARTHQUAKES IN AVACHA GULF (Kamchatka)

A.A. Skorkina1,2, A.A. Gusev1,3
1Kamchatka Branch of the Geophysical Survey, Russian Academy of Sciences, bul'v. B. Piipa 9, Petropavlovsk-Kamchatskii, 683006, Russia
2The Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, ul. B. Gruzinskaya 10/1, Moscow, 123242, Russia
3Institute of Volcanology and Seismology, Far Eastern Division, Russian Academy of Sciences, bul'v. B. Piipa 9, Petropavlovsk-Kamchatskii, 683006, Russia
Keywords: Earthquake, source spectra, scaling law, third corner frequency, f, source-controlled f, kappa

Abstract >>
The source spectra of M = 4.0-6.5 subduction earthquakes of 2011-2014 in Kamchatka are studied. The dataset comprises 1272 source spectra recovered from S waves of 372 earthquakes recorded by six digital rock-ground stations. The structure of the spectra is examined on the basis of a spectral model with three corner frequencies fc1, fc2 , and fc3. It was assumed that the spectra behave as f -2 between fc2 and fc3, where fc3 denotes source-controlled f max after Aki and Gusev. To determine the corner frequencies, we extracted the source spectrum from S- wave spectra using a previously developed attenuation model for the study area. The spectra were first reduced to the reference hard-rock station, employing a specially determined set of spectral amplifications of stations. We approximated the recovered source spectrum by a piecewise power-law function, estimated fc1, fc2, and fc3, and examined their dependence on the seismic moment M 0 (i.e., scaling). The dependence fc1 (M 0) does not contradict the hypothesis of source similarity when one expects . For fc2 and fc3, the scaling is close to and , respectively, indicating a clear violation of the similarity, especially prominent for fc3. Systematic identification of the frequency fc3, its determination, and analysis of its scaling are the main results of the study, important for understanding the physics of earthquake source processes. The use of fc3 as a source parameter in strong ground motion simulations will eliminate biases in estimating attenuation parameters, in particular, the spectral decay parameter «kappa.



9.
TRANSIENT ELECTRIC-FIELD RESPONSE TO A UNIFORM, MAGNETICALLY VISCOUS EARTH EXCITED BY A GROUNDED LINE SOURCE

E.Yu. Antonov1, N.O. Kozhevnikov1,2
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: Grounded line, equatorial array, transient response, magnetic viscosity, superparamagnetism, uniform earth

Abstract >>
A new method is suggested for calculation of transient electric-field response to conducting magnetically viscous earth excited by a grounded line source. Calculation algorithms are implemented in the computer program FwLL_MV. Using a conducting uniform, magnetically viscous half-space as an earth model, we have shown that magnetic relaxation affects the TEM response of equatorial and in-line arrays. As in the case of loop arrays, apparent resistivity steadily decreases with time. The higher the half-space resistivity and the shorter the offset, the earlier the voltage and the apparent resistivity begin to decrease as 1/ t . Magnetic relaxation and decay of eddy currents are independent processes within the range of resistivities typical of rocks.



10.
RECENT THERMAL REGIME OF LAKE ATOMIC (Semipalatinsk test site)

D.E. Ayunov1, A.D. Duchkov1, S.A. Kazantsev1, V.V. Romanenko2, S.B. Subbotin2
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Institute of Radiation Safety and Ecology of the National Nuclear Center, ul. Krasnoarmeiskaya 2, Kurchatov, 071100, Republic of Kazakhstan
Keywords: Underground nuclear explosion, Lake Chagan (Atomic), temperature measurements in lake water column, distribution of temperature and mineralization, meromictic lakes, Semipalatinsk test site

Abstract >>
We present results of the first research into the thermal regime of the water column of man-made Lake Atomic (Semipalatinsk test site) performed in 2013-2015. The temperature data have shown a two-layer stratification of the water column. In the upper layer (0-30 m) there are significant yearly temperature variations caused by seasonal climatic changes and wind-wave mixing. In the lower layer (30-80 m) there is a stable nonlinear temperature distribution. This lake can be classified as meromictic, whose upper layer consists of weakly mineralized «light water and lower one, of highly mineralized «heavy water. This stratification prevents seasonal mixing of waters of the entire column (from surface to bottom).