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Russian Geology and Geophysics

2016 year, number 8

1.
LATE TRIASSIC SILICEOUS-VOLCANO-TERRIGENOUS DEPOSITS OF THE CHUKCHI PENINSULA: COMPOSITION OF IGNEOUS ROCKS, U-Pb AGE OF ZIRCONS, AND GEODYNAMIC INTERPRETATIONS

G.V. Ledneva1, V.L. Pease2, B.A. Bazylev3
1Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017, Russia
2Department of Geological Sciences, Stockholm University, Svante Arrhenius vag 8, SE-106 91 Stockholm, Sweden
3Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia 2
Keywords: Geodynamic settings of magmatism, basaltic volcanism, U-Pb dating, Late Triassic, Velmay terrane, Chukchi Peninsula

Abstract >>
Study of Late Triassic volcanic, subvolcanic, and volcanosedimentary rocks of the Chukchi Peninsula (Velmay terrane) has shown their different geochemical types. Basalts, dolerites, and tuffs of the lower-middle strata of the Upper Triassic section bear evidence for their formation in suprasubductional geodynamic setting. Basalts and dolerites of the upper strata of this section correspond in composition to within-plate rocks and are similar to Middle-Late Triassic oceanic-plateau basalts and dolerites. U-Pb dating of magmatic zircons from tuffs of the lower-middle strata and from dolerites of the upper strata shows the almost synchronous magmatic activity in the suprasubductional (206 5 Ma) and within-plate (212 4 Ma) geodynamic settings.



2.
TRANSMANTLE (intratelluric) FLUID FLOWS: A NEW MODEL FOR PLUMES AND PLUME MAGMATISM

N.S. Zhatnuev
Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh'yanovoi 6a, Ulan-Ude, 670047, Russia
Keywords: Mantle plumes, transmantle flows, fluid fracturing, magma fracturing, fluid cavities, excess pressure

Abstract >>
A fluid model for the formation of mantle plumes is proposed. During the emission of gas from the Earths core, it accumulates as lenses at the core-mantle boundary. Reaching a critical size, the lenses burst out into the mantle and migrate to the surface. A relatively stationary transmantle fluid flow from the core-mantle boundary appears, which heats the mantle and the layer interacting with it. The flow stops in the base of the hard lithosphere and spreads laterally, causing its melting accompanied by the formation of magma chambers, which, reaching critical sizes, massively intrude and flow out.



3.
CARBONIFEROUS DEPOSITS IN THE BASEMENT OF THE SOUTHWESTERN WEST SIBERIAN GEOSYNECLISE (Kurgan Region)

S.V. Saraev1, T.P. Baturina1, A.Ya. Medvedev2, A.V. Travin3,4,5
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.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, 664033, Irkutsk, 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
5Tomsk State University, ul. Lenina 36, Tomsk, 634050, Russia
Keywords: Lower-Middle Carboniferous, Ar/Ar age, geochemistry of volcanics, sedimentation conditions, geodynamic settings, Tyumen-Kostanai trough

Abstract >>
The 40Ar/39Ar age of volcanics from the sections of core boreholes in the northern Tyumen-Kostanai trough (Kurgan Region) has been determined. The geologic structure of the northern part of the trough has been refined. The paleogeographic environments and geodynamic settings of formation of Carboniferous deposits have been established by sedimentological, petrological, and geochemical studies of the sections. In the Visean, marine environments with maximum basin depths were predominant. In the Kachar epoch (C1v3-s), the submarine relief of the basin became more complicated; blocks of older rocks appeared in the deposits. The geochemical indicator characteristics of the volcanics-contents of HFSE (Ti, Nb, Ta, Th, and Hf)-are close to those of andesitoids of island arcs and Andean-type active continental margins, as well as present-day andesites from the Kurile-Kamchatka zone. They are an order of magnitude lower than those in similar continental-rift volcanics, among which are volcanics of the Valeryanovka zone (according to some researchers). The contents of Ni, Co, and V are similar to those in island-arc andesites, including rocks of the Kurile-Kamchatka zone. The Ba/Ta and Ba/La ratios and the proportions of Th, Hf, and Ta in andesitoids of the Valeryanovka and Kachar Groups are close to the indicator characteristics of island-arc and active-continental-margin volcanics. The Kachar Group siliceous rocks are similar in the Rb/Zr-Nb, Fe-Nb, and Rb-(Y + Nb) correlations to rocks of mature island arcs and active continental margins. The incompatible-element and REE patterns for the Valeryanovka and Kachar volcanics are typical of island-arc volcanics, including rocks from the Kurile-Kamchatka zone. The indicator geochemical features and petrology of the volcanics and the sedimentologic features of the deposits testify to their formation on an Andean-type active continental margin (western margin of the Kazakhstan paleocontinent) in the Early-Middle Carboniferous.



4.
METAL-CONTAINING COALS OF THE EAST DONETSK BASIN: REGULARITIES OF FORMATION AND INTEGRATED-USE PROSPECTS

M.I. Gamov, S.V. Levchenko, V.G. Rylov, I.V. Rybin, A.V. Trufanov
Southern Federal University, Institute of Geosciences, ul. Zorge 40, Rostov-on-Don, 344090, Russia
Keywords: Fossil coals, fluidization processes, autoclave leaching, back shooting, coal use prospects, East Donetsk Basin

Abstract >>
We consider the regularities of formation and prospects for the integrated use of fossil coals of two conjugate lithogeodynamic groups: East Donetsk Basin group of coal-bearing deposits of suprarift genesis and platform group of coals of the southern slope of the Voronezh anteclise. The paleogeographic and lithologo-geochemical environments of formation of coal deposits in the Millerovo coal-bearing district and in the northeastern folded area of the Donetsk Basin are analyzed. The geochemical characteristics of coals with high contents of trace elements and their localization in the coal-bearing series (at the sites with hydrocarbon fluidization of coal seams) are discussed. We also assess the prospects for using coals and products of their conversion and burning as a specific mineral raw material containing nonferrous, rare, and noble metals.



5.
GOLD AND SILVER MINERALS IN LOW-SULFIDE ORES OF THE DZHULIETTA DEPOSIT (northeastern Russia)

G.A. Palyanova1,2, N.E. Savva3, T.V. Zhuravkova1,2, E.E. Kolova3
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
3N.A. Shilo Northeastern Complex Research Institute, Far Eastern Branch of the Russian Academy of Sciences, ul. Portovaya 16, Magadan, 685000, Russia
Keywords: Au- and Ag-containing pyrites, Au-Ag chalcogenides (acanthite, naumannite, uytenbogaardtite, petrovskaite), electrum, genesis, physicochemical parameters of ore formation

Abstract >>
Gold- and silver-containing pyrites of the Tikhii area at the Dzhulietta deposit (Engterinskii ore cluster, Magadan Region) were studied by optical and scanning electron microscopy and electron probe microanalysis. One- or two-phase rounded microinclusions consisting of electrum (450-680 ) and/or galena or of petrovskaite and/or uytenbogaardtite, galena, and sphalerite have been found in early pyrites. Later As-pyrites (up to 2.6 wt.% As) contain multiphase xenomorphic microinclusions of acanthite, uytenbogaardtite, freibergite, argentotetrahedrite-tennantite, naumannite, petzite, selenopolybasite-selenostephanite, tellurocanfieldite, and other ore minerals localized in pores, cracks, and interstices. Pyrites that underwent hypergene alterations have rims and veinlets formed by acanthite, goethite, anglesite, plattnerite, and native silver. The presence of rounded ore mineral microinclusions and large pores in the early pyrites suggests the participation of volatiles in the mineral formation and the uptake of large amounts of impurities by pyrite under high-gradient crystallization conditions. The thermobarogeochemical studies of fluid inclusions in quartz have shown that the ore zone formed under boiling-up of hydrothermal medium-concentration NaCl solutions at 230-105 ºC. The results of thermodynamic calculations evidence that Ag-Au-S-Se minerals formed under decrease in temperature and fugacity of sulfur (log10fS2 = -22 to -9) and selenium (log10fSe2 = -27 to -14) and change of reducing conditions by oxidizing ones in weakly acidic to near-neutral solutions.



6.
LITHIUM-CONTAINING Na-Fe-AMPHIBOLE FROM CRYOLITE ROCKS OF THE KATUGIN RARE-METAL DEPOSIT (Transbaikalia, Russia):CHEMICAL FEATURES AND CRYSTAL STRUCTURE

V.V. Sharygin1,2, N.V. Zubkova3, I.V. Pekov3, V.S. Rusakov4, D.A. Ksenofontov3, E.N. Nigmatulina1, N.V. Vladykin5, D.Yu. Pushcharovsky3
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
3Faculty of Geology, M.V. Lomonosov Moscow State University, Leninskiye Gory 1, Moscow, 119991, Russia
4Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskiye Gory 1-2, Moscow, 119991, Russia
5A.V. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Na-amphibole subgroup, ferro-ferri-fluoro-leakeite, ferro-ferri-fluoro-nybite, fluoro-riebeckite, fluoro-arfvedsonite, cryolite, alkali granites, Katugin deposit, Transbaikalia

Abstract >>
Detailed chemical and structural studies were carried out for Li-Na-Fe-amphibole from cryolite rocks of the Katugin deposit, Transbaikalia. The rocks contain 30-70 vol.% cryolite, mafic minerals as Fe-silicates (Li-Na-Fe-amphibole, Li-containing fluorannite, and bafertisite), oxides (magnetite, ilmenite, pyrochlore, cassiterite, and others), and sulfides (sphalerite, pyrite, and chalcopyrite). Quartz, K-feldspar, polylithionite, REE-fluorides, and albite occur as minor or accessory phases. The chemical composition of amphibole (wt.%) varies as follows: SiO2, 48.5-48.9; TiO2, 0.4-0.8; Al2O3, 1.6-2.2; Fe2O3, 15.9-17.1; FeO, 17.6-18.4; MnO, 0.8-0.9; ZnO, 0.3-1.1; MgO, 0.2-0.3; CaO, <0.1; Na2O, 8.4-8.7; K2O, 1.4-1.5; Li2O, 0.6-0.8; H2O, 0.7-0.8; and F, 2.2-2.5. The amphibole has a specific composition intermediate among the F-Fe members of the Na-amphibole subgroup: 40-45 mol.% ferro-ferri-fluoro-nybøite, 40-45 mol.% ferro-ferri-fluoro-leakeite, and 10-20 mol.% fluoro-riebeckite fluoro-arfvedsonite. The mineral is monoclinic, space group C 2/ m , a = 9.7978(2), b = 17.9993(3), c = 5.33232(13) Å, b = 103.748(2)º, V = 913.43(3) Å3, and Z = 2. The structural formula of Li-Na-Fe-amphibole is (Na0.46K0.240.30)Na2.00(Fe2+0.95Mg0.05)2(Fe3+0.95Ti0.025Mg0.025)2(Li0.37Fe2+0.48Mn0.10Zn0.05)[(Si0.91Al0.09)4Si4O22](F0.58(OH)0.42)2. Raman and Mössbauer spectroscopy data are given for this amphibole.



7.
QUANTITATIVE ANALYSIS OF MASS-TRANSFER DURING POLYMETAMORPHISM IN PELITES OF THE TRANSANGARIAN YENISEI RIDGE

I.I. Likhanov, V.V. Reverdatto
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences
Keywords: Metamorphism, chemical zoning of minerals, mineral reactions, major and trace elements, mass transfer analysis

Abstract >>
The study provides geological, structural, mineralogical, petrological, and geochronological evidence for polymetamorphic evolution of gneisses from the Garevka complex of the Yenisei Ridge. The results of the study provide significant insight into the geochemical behavior of major and trace elements in zoned garnet crystals and mineral inclusions formed during prograde and retrograde metamorphism of pelitic rocks. It was shown that the concentrations of Y and HREE in garnet decrease with increasing P and T and increase with decreasing pressure and temperature. The combined study of multicomponent chemical zoning patterns of coexisting minerals and metamorphic mineral reactions in metapelites was conducted. The results show that the main reason for a drastic increase in CaO content in garnets during collisional metamorphism is a mass exchange between garnet and plagioclase. The deviation from this trend, as indicated by the concurrent increase in the grossular content of garnet and anorthite content of plagioclase, arises from the breakdown of epidote. The calculated metamorphic reactions, mass balance analysis, and changes in mineral chemistry during metamorphism reinforce the evidence for the isochemical character of processes with respect to most components of the system. The minimum volume of the system in which chemical exchange between reacting phases is balanced for all major and trace elements did not exceed ~1 mm3. The total HREE balance requires a greater reaction volume (up to ~8 mm3) involved in the redistribution of these elements, which provide evidence for their relatively higher mobility during metamorphism relative to other rare earth elements. The specific distribution and quite substantial mass transport of HREE are controlled by heterovalent isomorphic substitution between these elements and CaO in garnet.



8.
PALEOBATHYMETRY OF THE LATE JURASSIC-NEOCOMIAN BASIN IN NORTHERN WEST SIBERIA AND THE IMPACT OF NATURAL PROCESSES

S.V. Ershov
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: Late Jurassic, Neocomian, clinoform, paleobathymetry, isostasy, West Siberian sedimentary basin

Abstract >>
Paleobathymetrical reconstructions were performed for the Volgian-Neocomian basin in northern West Siberia. The proposed technique takes into account a number of factors, such as the rates of basin subsidence and sedimentation, sediment lithification and types of lithology, sea level fluctuations, and isostasy. The role of each factor controlling the depth of the paleobasin is considered. The study reveals several stages of formation of the Neocomian clinoform complex of West Siberia, with different regimes of basin subsidence, sedimentation, and isostatic compensation.



9.
OXYGEN ISOTOPE COMPOSITION OF DIATOMS FROM SEDIMENTS OF LAKE KOTOKEL (Buryatia)

S.S. Kostrova1, H. Meyer2, P.E. Tarasov3, E.V. Bezrukova1,4, B. Chapligin2, A. Kossler3, L.A. Pavlova1, M.I. Kuzmin1
1Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
2Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Bdg. A43, Telegrafenberg, Potsdam, 14473, Germany
3Institute of Geological Sciences, Freie Universitaet Berlin, Bdg. D, Malteserstrasse 74-100, 12249, Germany
4Institute of Archeology and Ethnography, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Lavrentieva 17, Novosibirsk, 630090, Russia
Keywords: Isotope analysis, lacustrine sediments, biogenic silica, climate changes, hydrologic variation, southern Siberia

Abstract >>
This is a summary of new oxygen isotope record of diatoms from Lake Kotokel sediments, with implications for responses of the lake system and its environment to global change over the past 46 kyr. Fossil diatoms in all samples are free from visible contamination signatures and contain no more than 2.5 % Al2O3, which ensures reliable reconstructions. The δ18O values in diatoms vary between +23.7 and +31.2 over the record. The results mark mainly diatom assemblages of summer blooming periods, except for the time span between 36 and 32 kyr, when the isotopic signal records a shift from summer to spring blooming conditions. Possible water temperature changes only partly explain the changes in the isotopic record. The observed isotopic patterns are produced mainly by isotope changes in lake water in response to variations in air temperature, hydrology, and atmospheric circulation in the region. During Marine Isotope Stage (MIS) 2 (Last Glacial maximum), high δ18Odiatom resulted from rapid evaporation and low fluvial inputs. The high δ18Odiatom values of about +29 to +30 during the first half of MIS 1 (Holocene interglacial) suggest an increased share of summer rainfalls associated with southern/southeastern air transport. The δ18Odiatom decrease to +24 during the second half of MIS 1 is due to the overall hemispheric cooling and increased moisture supply to the area by the Atlantic air masses. The record of Lake Kotokel sediments provides an example of complex interplay among several climatic/environmental controls of δ18Odiatom during the Late Pleistocene and the Holocene.



10.
SEISMIC STRATIGRAPHY, FORMATION HISTORY AND GAS POTENTIAL OF THE NADYM-PUR INTERFLUVE AREA (West Siberia)

V.A. Kontorovich1,2, D.V. Ayunova1, I.A. Gubin1, S.V. Ershov1, A.Yu. Kalinin1, L.M. Kalinina1,2, M.S. Kanakov1, M.V. Solovev1,2, E.S. Surikova3, N.I. Shestakova3
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
3, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Reflector, seismic sequence, Cenomanian, tectonics, gas potential, structure, trap, pool, field

Abstract >>
The study presents a seismic and geological characterization of the Meso-Cenozoic sedimentary cover of the Nadym-Pur interfluve area and discusses the morphology of the Jurassic and Aptian-Albian-Cenomanian sedimentary complexes, formation history of structures, and geologic processes responsible for the formation of Cenomanian gas accumulations.