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Russian Geology and Geophysics

2020 year, number 3

1.
HIGH-PRESSURE PHASES IN THE DHOFAR 922 L6 CHONDRITE: RYSTALLIZATION OF OLIVINE-RINGWOODITE AGGREGATES AND JADEITE FROM MELT

I.S. Bazhan1, K.D. Litasov2,3, D.D. Badyukov4
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Kaluzhskoe shosse 14, Troitsk, Moscow, 108840, Russia
3Fersman Mineralogical Museum, Russian Academy of Sciences, Leninsky pr. 18/2, Moscow, 119071, Russia
4Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia
Keywords: Meteorite, chondrite, ringwoodite, majorite, jadeite, maskelynite, shock metamorphism

Abstract >>
High-pressure phases (ringwoodite, maskelynite, and jadeite) present as coarse-grained fragments in the shock-melt vein of the Dhofar 922 L6 chondrite were studied by scanning electron microscopy and Raman spectroscopy. Ringwoodite and jadeite crystallized from melted plagioclase and olivine fragments, respectively, at the cooling-decompression stage. We assume that the high contents of Fe and Mg in maskelynite-jadeite aggregates are due to a miscibility gap in the hedenbergite-jadeite and diopside-jadeite joins at ~600 and ~700 C, respectively. The P - T conditions of the formation of shock-melt veins are estimated at >19 GPa and >2150-2300 C.

DOI: 10.15372/RGG2019072
																				  																		



2.
ANKARAMITES OF GORNY ALTAI: MINERALOGICAL, PETROGRAPHIC, AND PETROCHEMICAL FEATURES OF DIOPSIDE PORPHYRY BASALTS OF THE UST-SEMA FORMATION

N. Khlif1,2, A.V. Vishnevskiy1,3, A.E. Izokh1,3
1Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
2Al-Furat University, Deir ez-Zur, Syria
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Academika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Ankaramite, high-Ca magma, clinopyroxene, Cr-diopside, Ural-Alaskan type, island arc magmatism, accretionary magmatism, middle Cambrian, Gorny Altai

Abstract >>
The mineral composition, petrography, and petrochemistry of middle Cambrian diopside porphyry basalts of the Ust-Sema Formation in Gorny Altai are considered in comparison with ankaramites of different geodynamic settings. The basalts of the Ust-Sema Formation are enriched in phenocrysts of high-Mg clinopyroxene (Mg# ≤ 94) (20 to 40-50 vol.%) with a high content of Cr2O3 (up to 1.11 wt.%), enclosed in the clinopyroxene-plagioclase microlitic groundmass. In addition, there are minor phenocrysts of saussuritized plagioclase (An49-71), olivine replaced by secondary minerals, amphibole with Mg# = 55.7-68.2, and Cr-spinel with Cr# = 36.2-41.7. Inclusions of Cr-spinel in high-Mg clinopyroxene are richer in Cr (Cr# ≤ 72.8). The basalts of the Ust-Sema Formation are chemically heterogeneous and are subdivided into two main groups: high-Ca (MgO = 7.98-14.77 wt.% and CaO/Al2O3 = 1.0-1.8) and low-Ca (MgO = 2.84-9.89 wt.% and CaO/Al2O3 = 0.2-0.9). The obtained data on the high-Ca basalts of the Ust-Sema Formation show that the rocks are similar to the reviewed ankaramites and thus can be assigned to this type of rocks. The low-Ca basalts of the Ust-Sema Formation might have resulted from the fractionation of ankaramitic melt in intermediate magma chambers. The Gorny Altai ankaramites formed through the melting of the wehrlitized suprasubductional lithospheric mantle during the closure of the Paleoasian Ocean.

DOI: 10.15372/RGG2019143
																				  																		



3.
GOLD-TELLURIDE-PALLADIUM MINERALIZATION, A NEW TYPE OF MINERALIZATION IN GABBRO-DOLERITES OF THE PAI-KHOI RIDGE (Yugor Peninsula, Russia)

R.I. Shaybekov1, N.V. Sokerina1, S.I. Isaenko1, N.N. Zykin2, S.N. Shanina1
1Yushkin Institute of Geology, Komi Science Center, Ural Branch of the Russian Academy of Sciences, ul. Pervomaiskaja 54, Syktyvkar, 167982, Russia
2LLC Gazprom VNIIGAZ, Proektiruemyi proezd 5537 15/1, s.p. Razvilkovskoe, Leninsky dist., Moscow region, 142717, Russia
Keywords: Gabbro-dolerite, Krutoi ore occurrence, Pai-Khoi Ridge, chalcopyrite-quartz veinlets, gold-telluride-palladium mineralization, fluid inclusions, gas chromatography, Raman spectroscopy

Abstract >>
Data on gabbro-dolerite pyrite-chalcopyrite-pyrrhotite, quartz vein sphalerite-chalcopyrite, and associated early and late gold-telluride-palladium mineralization of the Krutoi ore occurrence (Pai-Khoi Ridge, Yugor Peninsula) are presented. The early (magmatic) gold-telluride-palladium mineralization is represented by minerals of the ternary system Ag-Au-Cu, palladium antimonides and stibiotellurides, and platinum arsenides, and the late (hydrothermal) one, by minerals of the binary systems Au-Ag and Au-Pd as well as mercury, lead, and silver tellurides. Sudburyite and testibiopalladite have been first found in the Krutoi ore occurrence; moreover, testibiopalladite has been first discovered in the Pai-Khoi Ridge. Their chemical compositions and Raman spectra have been examined. The results of sulfide sulfur, oxygen, and carbon isotope studies of calcium-containing minerals of chalcopyrite-quartz veinlets suggest assimilation of the material of the host deposits by the ore-forming mantle fluids. The fluid inclusions in the veinlets are divided into nitrogen-methane and carbon dioxide-nitrogen according to the composition of the gas phase. It has been established that the mineral-forming fluids were poorly saturated with gas. Magnesium and calcium salts were predominant in them. The temperature of the formation of quartz in the chalcopyrite-quartz veinlets is close to 300-490 C, and sphalerite-chalcopyrite and associated late gold-telluride-palladium mineralization formed at temperatures not exceeding 260 C.

DOI: 10.15372/RGG2019156
																				  																		



4.
GEOCHEMISTRY OF METASEDIMENTARY ROCKS, SOURCES OF CLASTIC MATERIAL, AND TECTONIC NATURE OF MESOZOIC BASINS ON THE NORTHERN FRAMING OF THE EASTERN MONGOL-OKHOTSK OROGENIC BELT

V.A. Zaika1, A.A. Sorokin1, V.P. Kovach2, A.B. Kotov2
1Institute of Geology and Nature Management, Far Eastern Branch of the Russian Academy of Sciences, per. Relochnyi 1, Blagoveshchensk, 675000, Russia
2Institute of the Precambrian Geology and Geochronology, Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034, Russia
Keywords: Mesozoic depressions, sedimentary rocks, detrital zircons, sources, U-Th-Pb method, Lu-Hf method

Abstract >>
We present results of geochemical studies of the upper Mesozoic deposits of the Strelka and Malaya Tynda depressions and U-Th-Pb (LA-ICP-MS) geochronological and Lu-Hf isotope-geochemical studies of detrital zircons from these deposits. It is shown that the Strelka and Malaya Tynda depressions, adjacent to the Mongol-Okhotsk orogenic belt in the north and extending along the boundary between the southern framing of the North Asian Craton and the orogenic belt, are marginal troughs. These troughs are filled with thick beds of Mesozoic marine (at the bottom) and continental (at the top) metaterrigenous rocks, with an increase in the grain size of clastic material up the section; the rocks should be regarded as molasses. The results of U-Th-Pb geochronological studies of detrital zircons from metaterrigenous rocks of the Strelka and Malaya Tynda depressions, on the one hand, and the eastern part of the Mongol-Okhotsk Orogenic Belt, on the other, show that orogenic processes in the east of the belt were completed at the Early-Middle Jurassic boundary. The depressions began to form after the complete closure of the Mongol-Okhotsk basin and the formation of an orogenic structure at its place. Then they were filled with material supplied both from the Selenga-Stanovoi and Dzhugdzhur-Stanovoi superterranes on the southern framing of the North Asian Craton and from the Mongol-Okhotsk Belt, which was a mountain-folded structure in the Middle Jurassic.

DOI: 10.15372/RGG2019095
																				  																		



5.
GEOCHEMISTRY OF CARBONATES IN SMALL LAKES OF SOUTHERN WEST SIBERIA EXAMPLED FROM THE HOLOCENE SEDIMENTS OF LAKE ITKUL

A.E. Maltsev1, G.A. Leonova1, V.A. Bobrov1, S.K. Krivonogov2,3, L.V. Miroshnichenko1, Yu.S. Vossel1, M.S. Melgunov1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, ul. Pirogova 1, Novosibirsk, 630090, Russia
3Novosibirsk State University
Keywords: Carbonate sediments, calcite, aragonite, authigenic minerals, forms of occurrence and geochemistry of Ca, Sr, and Mn, diagenesis

Abstract >>
A 1.8 m thick core of the Holocene (7.9 14C kyr BP) sediments of Lake Itkul (Novosibirsk Region) has been studied. Based on the geochemical and lithostratigraphic properties of the bottom sediments, we have established the following stages of the lake evolution: (1) the beginning of sedimentation, 7.8-7.0 14 kyr BP; (2) extreme shallowing with a probable complete drying, ~7.0-5.5 14 kyr BP; (3) rise in the water level, ~5.5-4.3 14 kyr BP; (4) repeated shallowing, 4.3-2.8 14 kyr BP; and (5) subsequent watering, 2.8-0 14 kyr BP. At present, the lake again tends to shallowing. We have established that Lake Itkul has mineral sediments with a high content of carbonates (up to 64%). The high concentrations of HCO3- and Ca2+ and stable saturation (S/St > 1) of the surface water cause a shift of the carbonate-calcium equilibrium toward the carbonate formation. The studied authigenic carbonates are aragonite and fine-grained aggregates of poorly crystallized calcite particles with different Mg contents. Aragonite is both biogenic (mollusk and ostracode shells) and chemogenic (formed during the lake shallowing). In addition to carbonates, the lacustrine sediments contain mixed-layer aluminosilicates, feldspars, and quartz. The presence of pyrite throughout the sediment section indicates reducing conditions and the activity of sulfate-reducing microorganisms. Carbonates (especially aragonite) are significantly enriched in strontium. Manganese does not form its own minerals but is present as an isomorphic impurity in authigenic carbonates.

DOI: 10.15372/RGG2019081
																				  																		



6.
PROBABILISTIC ESTIMATION OF THE HELIUM RESOURCES IN THE CENTRAL AND SOUTHERN AREAS OF THE LENA-TUNGUSKA PETROLEUM PROVINCE

L.M. Burshtein1, A.E. Kontorovich1,2, V.R. Livshits1,2, S.A. Moiseev1, E.S. Yaroslavtseva1
1Trofimuk 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 1, Novosibirsk, 630090, Russia
Keywords: Gas, helium, resources, reserves, probabilistic estimation, Lena-Tunguska province

Abstract >>
We propose and test a method for probabilistic estimation of the scale and structure (distribution of helium concentrations in free gas, accumulations of different sizes, localization zones, and stratigraphic complexes) of helium and helium-containing gas resources. Summarizing the available geological information about the structure of the sedimentary cover and data on the revealed accumulations of helium-containing gases, we have first made probabilistic estimation of the scale and structure of their resources as well as helium resources in the central and southern areas of the Lena-Tunguska province. The forecast results will serve as a reliable basis for geological and economic estimation of helium resources, for long-term planning of gas field development in East Siberia and the Republic of Sakha, and for helium industrialization in these regions.

DOI: 10.15372/RGG2019172
																				  																		



7.
FACIES-STRATIGRAPHIC ZONATION OF THE CALLOVIAN-KIMMERIDGIAN DEPOSITS OF THE WEST SIBERIAN SEDIMENTARY BASIN

S.V. Ryzhkova1,2, L.G. Vakulenko1,2, V.A. Kazanenkov1, A.E. Kontorovich1,2, V.A. Kontorovich1,2, B.L. Nikitenko1,2, B.N. Shurygin1,2, E.V. Borisov1, L.M. Kalinina1, A.Yu. Nekhaev1, E.V. Ponomareva1, M.A. Fomin1,2, P.A. Yan1,2
1Trofimuk 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 1, Novosibirsk, 630090, Russia
Keywords: Callovian-Kimmeridgian deposits, petroliferous horizon Yu, facies-stratigraphic zoning, West Siberia

Abstract >>
We propose a facies-stratigraphic zoning of the Vasyugan and Georgievka horizons in the sedimentary cover of the West Siberian Basin, including the southern part of the Kara Sea. Based on the typification of well sections and taking into account the paleogeography of the Callovian-Kimmeridgian deposits, we have recognized 12 regions with different structures of the Vasyugan and Georgievka horizons. The Purpei-Vasyugan area is divided into three subareas according to the structure of the Vasyugan Formation including the petroliferous horizon Yu1. Transition zones have been recognized between the Vasyugan Formation and the bordering Abalak, Tatar, and Naunak formations along the western, southern, and eastern boundaries of the area, respectively. The results of zoning of the Callovian-Kimmeridgian deposits, including the petroliferous horizon Yu1, can be used on planning of exploration work, for selecting standard facies models, and for predicting the petrophysical properties of a reservoir.

DOI: 10.15372/RGG2019098
																				  																		



8.
MODERN METHODS FOR JOINT ANALYSIS AND INVERSION OF GEOPHYSICAL DATA

V.V. Spichak
Geoelectromagnetic Research Center of Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Troitsk, Moscow, 108840, Russia
Keywords: Geophysical data, joint analysis, inversion, correlation, artificial neural network, cluster analysis

Abstract >>
This is an overview of existing methods for joint analysis and inversion of geophysical data, including conventional techniques and alternative options based on simultaneous and sequential inversion of different data sets and posterior analysis of separate inversion results. Advantages and disadvantages of different methods are compared using examples of typical cases, and the respective practical recommendations are provided for each method.

DOI: 10.15372/RGG2019092