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Russian Geology and Geophysics

2017 year, number 5

1.
MODELING OF THE FORMATION OF NONISOTHERMAL ZONING IN MAGNESIAN SKARNS IN THE ORE-MAGMATIC FLUID SYSTEMS OF INTRUSIVE TRAPS OF THE SOUTHERN SIBERIAN PLATFORM

M.P. Mazurov1,2, V.G. Bykova3
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh'yanovoi 6a, Ulan-Ude, 670047, Russia
Keywords: Magnesian skarns, dolerites, metasomatism, numerical modeling

Abstract >>
Using the Selector PC application and a stationary flow reactor, we studied the process of formation of magnesian skarns at the contact of dolerites with carbonate-salt deposits. The physicochemical parameters of metasomatic processes were estimated by studying the localization of skarn ore shoots and mineral assemblages in the deposits of the Angara-Ilim type. The action of magmatic fluids on the system dolerite-magnesian salt deposits and dolerite-carbonate-salt deposits resulted in zonal columns of infiltration magnesian skarns. The computation was carried out using a dynamic multireservoir model of a flow reactor with a constant temperature gradient and a uniform pressure. We have established that changes in the C/H ratio and Cl content in the fluid source affect the composition of the produced mineral assemblages. Depending on the temperature during the formation of skarns, different mineral assemblages are produced: diopside, enstatite, anorthite, quartz, ilmenite, hercynite, and pyrrhotite at 1040-1010 ºC; monticellite, forsterite, magnetite, geikielite, periclase, spinel, calcite, and graphite at 980-740 C; and calcite, dolomite, phlogopite, halite, and graphite at 710-380 C. Wollastonite is observed in the rear zone of magnesian skarns. We examined the temperature-dependent sequence of formation of different types of silicates, spinels, and Ti-containing minerals in the metasomatic column. The computation results show that during crystallization, the tholeiitic magma releases a fluid phase with C/H = 0.1-1.0, amounting to 1.5-2.0 wt.%.



2.
SIMULATION OF NONISOTHERMAL METASOMATISM OF PERIDOTITE FROM MANTLE WEDGE BENEATH THE AVACHA GROUP OF VOLCANOES (Kamchatka)

V.N. Sharapov1,2, G.V. Kuznetsov1, T.Yu. Timina1, A.A. Tomilenko1, K.V. Chudnenko3
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Infiltration metasomatism, dynamics, zoning, mantle wedge

Abstract >>
Comprehensive studies of mineralogy, fluid and melt inclusions, and gas phase in minerals from a representative collection of peridotite xenoliths that underwent metasomatism and convective partial melting in the mantle wedge beneath Avacha Volcano were used to simulate interactions between mantle wedge material and magmatic fluids of constant and variable compositions at different depths, as well as metasomatic effects of fluids derived from subduction slabs. The obtained virtual dynamic patterns of metasomatic zoning across the mantle wedge show how composition variations of fluids and PT conditions at their sources influence the facies of metasomatized mantle wedge harzburgite. The compositions of the Avacha xenoliths and crustal rodingite from Kamchatka compared with results of physicochemical modeling suggest that eruptions of Avacha Volcano brought metasomatized material of the upper mantle wedge to the surface. The rocks underwent multistage metasomatism along cracks in a relatively narrow temperature range. Such processes are apparently common to seismically deformed permeable lithosphere above magma reservoirs. However, the mineralogical zoning of the Kamchatka crustal rhodingites differs from that in cracked metasomatic peridotite above the sources of magmatic fluids in the mantle wedge beneath the Kamchatka arc.



3.
MIGRATION OF FLUIDS AND MELTS IN SUBDUCTION ZONES AND GENERAL ASPECTS OF THERMOPHYSICAL MODELING IN GEOLOGY

N.L. Dobretsov1,2, V.A. Simonov3,2, I.Yu. Koulakov1,2, A.V. Kotlyarov3
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
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Fluid, melt, subduction zone, mantle wedge, magma reservoir, peridotite, melt inclusion, seismic tomography, Avacha Volcano, Kamchatka

Abstract >>
Modeling of fluid-magmatic systems in a suprasubduction mantle wedge is considered for the case of Kamchatka with reference to data on peridotites from other known subduction and oceanic rock complexes. This modeling has to take account of magma storage in several intermediate reservoirs at different depths, up to six such reservoirs, as in the case of Avacha Volcano. Comparison of available data on melt inclusions in spinels indicates crystallization of the Avacha peridotites in magmatic systems progressively decreasing in temperature (>1200 C → >1100 C → >900 C) and pressure (from 13.8 to 4.5 kbar) in intermediate reservoirs at depths of 30-40 and 15-20 km. The Avacha harzburgites do not belong to primary oceanic mantle as they lack both signatures of high-temperature plastic flow and effects of mantle melts known for sheared mantle peridotites from ophiolite suites. The vP / vS ratio estimated from jointly analyzed P - and S -wave velocities ( vP and vS , respectively), an important indicator for seismic tomographic reconstructions of subduction zones, allows discriminating between regions saturated mainly with liquid (melts) and gas phases beneath volcanoes. Only specially tested tomographic data can provide reliable reference for modeling of mantle wedge processes.



4.
ORGANIC GEOCHEMISTRY OF THE LOWER CAMBRIAN SINYAYA FORMATION (northern slope of the Aldan anteclise)

T.M. Parfenova1,2, I.V. Korovnikov1,2, V.G. Eder1, V.N. Melenevskii1
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: Organic geochemistry, bitumens, biomarkers, source rocks, Lower Cambrian, Siberian Platform

Abstract >>
We investigated organic matter (OM) of the Lower Cambrian Sinyaya Formation in the southeast of the Siberian Platform. The studied collection of rocks was divided into groups according to the contents of organic carbon, bitumens, and sulfur and lithologic characteristics. The content and distribution of saturated biomarkers were examined. Lanostanes C30, norlanostanes C29, 28,30-bisnorhopanes, and 2α- and 3β-methylhopanes have been identified in the bitumens. Relationships between the content of organic carbon and the distribution of hopanes, hopane ratios, and 2α-methylhopane index have been established. The conditions of sedimentation, diagenesis, and catagenesis of OM and the generation potential of the rocks have been estimated. It is showb that lanostanes, 28,30-bisnorhopanes, and methylhopanes can be used as biomarkers of the source rocks of the Sinyaya Formation and thus can help to determine the source of bitumens on the northern slope of the Aldan anteclise of the Siberian Platform.



5.
INPUT OF ORGANIC MATTER TO THE BUOR-KHAYA GULF (Laptev Sea)

T.V. Pogodaeva1, T.V. Khodzher1, N.A. Zhuchenko1, M.N. Grigoriev2, V.S. Panov3, G.T. Maksimov2
1Limnological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Ulan-Batorskaya 3, 664033, Russia
2Melnikov Permafrost Institute, ul. Merzlotnaya 36, Yakutsk, 677010, Russia
3Institute of Archeology and Ethnography, Siberian Branch of the Russian Academy of Sciences, pr. Akad. Lavrentieva 17, Novosibirsk, 630090, Russia
Keywords: Bottom sediments, organic carbon, organic nitrogen, carbon isotopes, nitrogen isotopes, Arctic, Laptev Sea

Abstract >>
We present results of study of organic matter in the coastal and bottom sediments of the Laptev Sea (Buor-Khaya Gulf). The study has shown the regularities of organic-matter distribution in the shelf zone adjacent to the glacial coast. The coast composed of a glacial rock complex supplies the largest amount of organic material to the sea as compared with other types of the coast. The average content of organic matter in these strata is ~2-3 wt.%. The bottom sediments of the shallow littoral zone are significantly depleted in organic carbon (0.1-0.3%) as a result of their active rewashing and the transition of finely dispersed material (mainly organic one) toward the deep sea zones. The content of organic carbon in the bottom sediments increases to 1-2% as the sea deepens to 7-10 m at 5-12 km from the coast. There are frequent local anomalies of organic-carbon contents (up to 4-5%) in the deltaic zones of the sea. The highest contents of organic carbon (up to 3%) have been found in the recent marine sediments in the central, relatively deep zones of the bays.



6.
SPATIAL-TEMPORAL COLLOCATION AND GENETIC RELATIONSHIP AMONG URANIUM, COAL AND HYDROCARBONS AND ITS SIGNIFICANCE FOR URANIUM PROSPECTING: A CASE FROM THE MESOZOIC-CENOZOIC URANIFEROUS BASINS, NORTH CHINA

Z. Feng1,2,3, F. Nie1, J. Deng4, H. Zhang5, B. Liu2
1Key Laboratory of Nuclear Resources and Environment, Ministry of Education, East China University of Technology, Nanchang, Jiangxi, 330013, China
2National Deep Sea Center, Qingdao, Shandong, 266061, China
3College of Marine Geoscience, Ocean University of China, Qingdao, Shandong, 266061, China
4Fundamental Science on Radioactive Geology and Exploration Technology Laboratory, East China University of Technology, Nanchang, Jiangxi, 330013, China
5Geological Party No. 216 BOG CNNC, Wulumuqi, Xinjiang, 830011, China
Keywords: Hydrocarbon-coal-uranium, energy basin, spatiotemporal allocation, uranium mineralization, genetic relationship

Abstract >>
The fact that uranium, coal, oil, and other ores occur in the same sedimentary basin has been extensively recognized. By comparing the spatial and temporal relationships among uranium, coal, and hydrocarbons, we found that the ore-bearing uranium and coal layers within the same basin are commonly interbedded or adjacent to each other. In general, however, uranium deposits are spatially distant from oilfields. We analyzed the genetic relationship among oil, coal, and uranium by compiling numerous geological surveys, test analyses, and previous studies of the Ili, Songliao, and other basins in North China. It is considered that the mild and humid paleoclimate should be an important factor affecting the formation of coal reservoir, mudstone as the upper and lower aquifuges, and the host rocks with rich organic matter. Thus, these coal-mining areas occurring at the edges of basins deserve to be studied in detail for uranium exploration. In addition, the metallogenic epochs are roughly similar to the epochs of hydrocarbon migration and tectonic events. These existing data of oil exploration can be used to unravel the regional and local tectonic evolutions of the basin related to uranium mineralization. Finally, a rough relationship between uranium mineralization and hydrocarbons was presented. Note that hydrocarbon is not just beneficial for the formation of uranium deposits but may also inhibit the transportation and mineralization of uranium-bearing materials. Regions with shallow hydrocarbon fields or large quantities of hydrocarbon dissipation are not the ideal exploration locations for uranium.



7.
TRANSIENT CHARACTERISTICS OF INDUCED POLARIZATION IN INHOMOGENEOUS MEDIA (from results of 2D numerical modeling)

G.V. Gurin1, A.V. Tarasov1,2, Yu.T. Ilin2, K.V. Titov2
1VIRG-Rudgeofizika, Petrogradskaya nab. 18, korp. 3V, St. Petersburg, 197046, Russia
2Institute of Earth Sciences, St. Petersburg State University, per. Dekabristov 16, St. Petersburg, 199155, Russia
Keywords: Induced polarization, mathematical modeling, relaxation time, chargeability, disseminated ores

Abstract >>
The paper presents results of 2D mathematical modeling of induced polarization (IP) in the cases of profiling and tomography for piecewise media containing orebodies with different structures, sizes, depths, relaxation times, chargeability, and electrical resistivity. The standard and spectral approaches to data analysis are compared. The cases when analysis of transient IP characteristics yields new information of practical importance are considered. The main features of transient IP characteristics in 2D inhomogeneous media are determined from the modeling results. Analysis of transient IP characteristics yields the best results when the depth of occurrence of polarizable bodies is minimum and their electrical conductivity is an order of magnitude lower than that of the host rock.



8.
A NEW APPROACH TO SHALLOW-DEPTH ELECTROMAGNETIC SOUNDING

E.V. Balkov1, D.I. Fadeev1,2, Yu.G. Karin1, A.K. Manshtein1, Yu.A. Manshtein1,2, G.L. Panin1
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: Frequency and geometric sounding, electromagnetic profiling, primary-field compensation

Abstract >>
This paper presents an extensive review of currently available shallow-depth portable geophysical instrumentation for electromagnetic induction sounding and profiling and the main technical characteristics of the devices. A new ground-based multicoil shallow-depth device with a special arrangement of receiver coils is considered. The latter are placed on the line where the vertical component of the magnetic field from the source coil is zero. The spacing between the source and the receivers is used as a sounding parameter, along with a frequency. This increases the efficiency of the study of the upper section and the contrast between the sounding curves, which simplifies their interpretation. In studies of local anomalous objects, the use of the proposed method and instrumentation significantly improves the quality of geophysical data. The increase in sounding efficiency provided by these devices is demonstrated on both synthetic and real field data.



9.
LABORATORY MODELING AND MEASUREMENT OF THE ELECTRICAL RESISTIVITY OF HYDRATE-BEARING SAND SAMPLES

M.E. Permyakov1, N.A. Manchenko1, A.D. Duchkov1, A.Yu. Manakov2, A.N. Drobchik1, A.K. Manshtein1
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2A.V. Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Lavrentieva 3, Novosibirsk, 630090, Russia
Keywords: Tetrahydrofuran, tetrahydrofuran hydrates, modeling of hydrate-bearing samples, electrical resistivity

Abstract >>
We describe a setup for modeling hydrate-bearing rock samples and measuring their electrical resistivity at different pressures and temperatures using an AMNB cylindrical four-electrode probe. Methods for modeling hydrate-bearing rock samples and measuring their resistivity are considered. The setup was used in a series of experiments to measure the resistivity of sand samples containing water, ice, or tetrahydrofuran (THF) hydrate. It is shown that when the rock pores contain hydrates and a partially unfrozen aqueous solution of NaCl and THF, the electrical resistivity is determined by the high resistivity of the solution and increases with the formation of hydrate. The presence of THF hydrate in the experimental samples increased their resistivity by 180-320 Ohmm at a temperature of about 0 C. After the formation of hydrate and freezing of residual water, the resistivity of the sample is stabilized at 70-80 kOhmm at a temperature of -15 C.



10.
INVERSION OF MAGNETOTELLURIC DATA IN THE FAULT ZONES OF GORNY ALTAI (based on a 3D model)

V.V. Plotkin, E.V. Pospeeva, D.I. Gubin
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: Magnetotelluric sounding, electrical conductivity, distortions and the normalization of MTS curves, surface and depth inhomogeneities, geoelectric section, recent faults, Cenozoic activity

Abstract >>
Results of magnetotelluric sounding (MTS) in Gornyi Altai are interpreted on the basis of a numerical model of MTS curve distortions in a 3D earth. The distortions are modelled using the Trefftz method permitting the application of models of different degrees of similarity to the test medium (depending on the available computation tools). The major advantage of this approach is demonstrated. There is no need to choose between different MTS curves (transverse and longitudinal, minimum and maximum, undistorted and distorted). Procedures of normalization of these curves become unnecessary. All recorded curves are used in full measure as input data for their inversion. Optimization of the model of the medium with regard to the distortion of MTS curves caused by surface and depth inhomogeneities improves the reliability of geoelectric sections.