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Russian Geology and Geophysics

2016 year, number 11

1.
CENOZOIC HISTORY OF TOPOGRAPHY IN SOUTHEASTERN GORNY ALTAI: THERMOCHRONOLOGY AND RESISTIVITY AND GRAVITY RECORDS

N.L. Dobretsov1,2, M.M. Buslov3,2, A.N. Vasilevsky1,2, E.V. Vetrov3,4, N.N. Nevedrova1,2
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
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
4Siberian Research Institute of Geology, Geophysics, and Mineral Deposits, Krasnyi pr. 67, Novosibirsk, 630091, Russia
Keywords: Neotectonics, plateau, strike-slip fault, thrust, ramp, fission-track thermochronology, resistivity and gravity fields, Gorny Altai

Abstract >>
The Central Asian Orogen was reactivated in the Cenozoic, which gave rise to mountain systems and sedimentary basins, strike-slip and thrust faults, ramps, and rift basins under the far-field effect of the India-Eurasia collision. Pre-Cenozoic structures, as well as the superposed Cenozoic deformation, are traceable in the gravity pattern. Analysis and correlation of stratigraphic, tectonic, geomorphological, and geophysical (resistivity and gravity) data from Gorny Altai and tectonic modeling on the basis of apatite fission-track thermochronology show that vertical motions have been the most active for the past 5 Ma. The uplift and subsidence produced, respectively, the Chulyshman and Ukok plateaus with high mountains around and the the Kurai-Chuya basin between them. Gravity data suggest the existence of Late Carboniferous, Jurassic, and Cretaceous rocks found in tectonic wedges around the basin at the base of its sedimentary fill.



2.
PARAMETERS OF PLUMES OF NORTH ASIA

A.G. Kirdyashkin1, A.A. Kirdyashkin1,2
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
Keywords: Experimental and theoretical modeling, thermochemical plumes, free-convection flows, thermal power, large igneous provinces, batholiths, rift zones

Abstract >>
This paper presents the thermal and hydrodynamic structure of the conduit of a thermochemical mantle plume based on the results of experimental and theoretical modeling of thermochemical plumes. The basic relations for determining the thermal power and diameter of plumes are given. Depending on the geodynamic setting of eruption, the following types of plumes are distinguished: plumes responsible for the formation of large igneous provinces (LIP); plumes with a mushroom-shaped head, responsible, in particular, for batholith formation; and plumes producing rift zones. Using geological data (extent of magmatism, age of igneous provinces, and sizes of igneous areas), we estimated the parameters of plumes in Siberia and its folded framing: mass flow rate of melt, thermal power, depth of origin, and diameters of plume conduits and heads. The plumes responsible for the formation of the Siberian LIP (relative thermal power Ka = 114.9) and the West Siberian rift system (Ka = 37.8 for each of the three plumes) originated at the core-mantle boundary and discharged in the presence of a refractory layer in the lithosphere. The Vilyui plume (Ka = 27.3) originated at the core-mantle boundary and caused the formation of a rift system in the absence of a refractory layer. The plumes that produced the Hangayn (Ka = 6.8) and Henteyn (Ka = 5.5) batholiths were initiated at the core-mantle boundary and had mushroom-shaped heads. The plumes responsible for the formation of rift zones might have originated at the 670 km discontinuity.



3.
NEOPROTEROZOIC METAVOLCANOSEDIMENTARY ROCKS OF THE BOZDAK GROUP IN SOUTHERN ULUTAU (Central Kazakhstan): ISOTOPE-GEOCHEMICAL AND GEOCHRONOLOGICAL DATA

N.V. Dmitrieva1,2, E.F. Letnikova1,2, S.I. Shkolnik3, I.A. Vishnevskaya1,2, N.A. Kanygina4, M.S. Nikolaeva1, I.V. Sharf5
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
3Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
4Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017, Russia
5Tomsk Polytechnic University, pr. Lenina 30, Tomsk, 634050, Russia
Keywords: Late Precambrian, volcanosedimentary rocks, LA-ICP-MS zircon dating, Sm-Nd isotopes, Central Kazakhstan

Abstract >>
We consider geochemistry of Neoproterozoic metavolcanosedimentary rocks of the Bozdak Group in southern Ulutau (Central Kazakhstan) and present the first results of U-Pb LA-ICP-MS dating of clastic zircons and Sm-Nd isotope data. Isotope-geochemical and geochronological studies have shown that the Bozdak Group rocks resulted from the destruction of igneous and metamorphic complexes mostly of Neoproterozoic age with the participation of Archean and Paleoproterozoic rocks. The lower boundary of sedimentation is dated at 800 Ma. The obtained isotope-geochemical data on the Bozdak Group basaltoids suggest their formation on thick continental crust with the participation of subduction fluid.



4.
GEOCHEMICAL, ISOTOPIC, AND GEOCHRONOLOGICAL EVIDENCE FOR SUBSYNCHRONOUS ISLAND-ARC MAGMATISM AND TERRIGENOUS SEDIMENTATION (Predivinsk terrane of the Yenisei Ridge)

A.D. Nozhkin1, N.V. Dmitrieva1,2, I I. Likhanov1, P.A. Serov3, P.S. Kozlov4
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, Kola Scientific Center of the Russian Academy of Sciences, ul. Fersmana 14, Apatity, 184209, Russia
4A.N. Zavaritsky Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences, Pochtovyi per. 7, Yekaterinburg, 620075, Russia
Keywords: Late Precambrian, volcanosedimentary rocks, LA-ICP-MS dating, SHRIMP II, Sm-Nd isotopy, Predivinsk terrane, Yenisei Ridge

Abstract >>
In this study we present data on the geologic setting, geochemical and isotopic compositions, timing and P - T conditions of metamorphism of Neoproterozoic terrigenous metasediments, and associated island-arc metavolcanics of the Predivinsk terrane of the Yenisei Ridge. Relatively immature terrigenous rocks were eroded from a local source which is associated with island-arc magmatic complexes. The geochronological constraints indicate that the terrigenous rocks were eroded from juvenile crustal sources represented primarily by magmatic rocks, which are similar to those of the Predivinsk terrane. This is supported by a similar range of model ages, positive εNd values of terrigenous and magmatic rocks, and correspondence between the concordant ages of detrital zircons from metasedimentary rocks (610-640 Ma) and the U-Pb ages of zircons from rhyolites (ca. 620-640 Ma) from two suites within different sequences. The P-T conditions for volcanosedimentary rocks of the Predivinsk terrane correspond to the epidote-amphibolite facies and the transition from epidote-amphibolite to amphibolite facies. The most likely age of metamorphism due to Vendian accretion/collision events is given by Ar-Ar dates of 600-610 Ma.



5.
MESOZOIC GRANITOIDS IN THE STRUCTURE OF THE BEZYMYANNYI METAMORPHIC-CORE COMPLEX (western Transbaikalia)

T.V. Donskaya1, D.P. Gladkochub1, A.M. Mazukabzov1, T. Wang2,3, L. Guo2, N.V. Rodionov4, E.I. Demonterova1
1Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing, 100037, China
3Beijing SHRIMP Center, Chinese Academy of Geological Sciences, Beijing, 100037, China
4A.P. Karpinsky Russian Geological Research Institute, Srednii pr. 74, St. Petersburg, 199106, Russia
Keywords: Granites, U-Pb zircon age, metamorphic-core complexes, Mesozoic, western Transbaikalia

Abstract >>
We performed geological, geochronological, and isotope-geochemical studies of two tectonized-granite bodies intruding the rocks of the lower plate of the Bezymyannyi metamorphic-core complex (MCC) (western Transbaikalia). The U-Pb zircon age of sheared granites sampled on the periphery of the Bezymyannyi MCC near the detachment zone is 202 2 Ma (LA-ICP-MS). The U-Pb dating (SHRIMP-II) of zircon grains from gneissic granite intruding the rocks of the lower plate in the central zone of the Bezymyannyi MCC has yielded an age of 165 2 Ma. The sheared granites dated at 202 Ma (Late Triassic) have low contents of Nb and Ta and high contents of Sr and Ba, probably inherited from magmatic subduction-related sources. These granites are characterized by εNd(T) = -3.7, which, along with the high contents of K2O and medium contents of Th, testifies to the presence of continental-crust material in their source. Thus, they formed, most likely, from a mixed mantle-crust source. The studied granites, like other Triassic igneous rocks in Transbaikalia, might have originated in the suprasubduction setting during the evolution of the active continental margin of the Siberian continent. The gneissic granites dated at 165 Ma (Middle Jurassic) have high contents of K2O, Rb, and Th, are depleted in Nb, and are characterized by εNd(T) = 0 and a negative Eu anomaly on the REE patterns. They formed, most likely, from an intermediate-felsic crustal source. These Middle Jurassic granites, like other small Jurassic granitoid massifs spatially associated with MCCs in western Transbaikalia, intruded in the western part of the Mongol-Okhotsk Ocean after its closure, during the change of the subduction regime for the collisional one. The studied Late Triassic granites of the Bezymyannyi MCC cannot be associated with MCCs in Transbaikalia because their intrusion was related to the subduction of the oceanic plate of the Mongol-Okhotsk Ocean beneath the Siberian continent. The Middle Jurassic granites of the Bezymyannyi MCC, together with other small Jurassic granitoid massifs, can be classified as prekinematic intrusions formed earlier than MCCs in western Transbaikalia. However, it is unlikely that their intrusion caused a large-scaled crustal extension in Transbaikalia.



6.
CLASSIFICATION OF ROCKS OF THE BAZHENOV FORMATION

A.E. Kontorovich, P.A. Yan, A.G. Zamirailova, E.A. Kostyreva, V.G. Eder
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: Petroleum source rocks, rock classification, Bazhenov Formation, West Siberia

Abstract >>
In this study we propose a new classification of rocks of the Bazhenov Formation based on the proportions of four principal components (siliceous, clay, and carbonate minerals and organic matter (kerogen)) of mostly biochemogenic and, to a lesser extent, allothigenic origin. The classification is based on the results of mineralogical and chemical analyses of more than 400 core samples from 15 wells drilled within the Bazhenov Formation, West Siberian petroleum basin. Four major classes of rocks, divided into 16 subclasses, have been recognized. The terms mixtite and kerogen-rich rock are introduced. Mixtites (biochemogenic mixtites) are defined as a class of rocks containing less than 50% of each component, including kerogen. It was shown that the most common rocks of the Bazhenov Formation are siliceous-argillaceous, kerogen-siliceous, and kerogen-argillaceous-siliceous mixtites and kerogen silicites, which together account for ~65% of all samples analyzed. The proposed approach can be used to study organic-rich black shales in different sedimentary basins worldwide.



7.
DEEP SEISMIC STRUCTURE OF THE BOUNDARY ZONE BETWEEN THE EURASIAN AND OKHOTSK PLATES IN EASTERN RUSSIA (along the 3DV deep seismic sounding profile)

V.M. Solovev1,2, V.S. Seleznev3,2, A.S. Salnikov4, S.V. Shibaev5, V.Yu. Timofeev2, A.V. Liseikin1, A.E. Shenmaier1
1Altai-Sayan Branch of the Geophysical Survey, 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
3Geophysical Survey, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
4Siberian Research Institute of Geology, Geophysics and Mineral Raw Materials, Krasnyi pr. 67, Novosibirsk, 630091, Russia
5Yakutian Branch of the Geophysical Survey, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: DSS profiles, Moho, boundary and average velocities, seismicity, continental plates, plate boundaries, hypocenters of earthquakes

Abstract >>
Analysis of geological and geophysical data on the boundary zones between the Eurasian plate and other plates shows poor knowledge of the deep structure of the region. This information data will help to refine the position of the plate boundaries and the structure of the Earths crust and mantle. We present data on the seismicity and deep structure along the deep seismic sounding (DSS) profile running across the boundary between the Eurasian and Okhotsk plates. A comprehensive analysis of the DSS materials and seismic data shows a significant expression of this boundary zone both in the deep Earths crust structures and in the Moho. A zone of anomalous seismicity and deep structure extends along the DSS profile for several hundred kilometers. We have refined the position of the main boundary between the Eurasian and Okhotsk plates, which passes approximately along 144ºE.



8.
RECENT DEFORMATIONS OF THE AMURIAN PLATE AND SURROUNDING STRUCTURES (data from GPS measurements)

S.V. Ashurkov1,2, V.A. Sankov1,3, M.A. Serov4, P.Yu. Lukyanov5, N.N. Grib6, G.S. Bordonskii5, M.G. Dembelov7
1Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2Institute of Diamond and Precious Metal Geology, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
3Irkutsk State University, ul. K. Marksa 1, Irkutsk, 664003, Russia
4Institute of Environment and Nature Management, Far East Branch of the Russian Academy of Sciences, ul. B. Khmelnitskogo 2, Blagoveshchensk, 675000, Russia
5Institute of Natural Resources, Environment, and Geocryology, Siberian Branch of the Russian Academy of Sciences, ul. Butina 26, Chita, 672000, Russia
6Technical Institute, Filial of Amosov North-Eastern Federal University, ul. Yuzhno-Yakutskaya 23, Neryungri, 678960, Russia
7Institute of Physical Material Science, Siberian Branch of the Russian Academy of Sciences, ul. Sakhiyanovoi 6, Ulan-Ude, 670047, Russia
Keywords: Contemporary crustal movements, crustal deformations, GPS measurements, Amurian Plate

Abstract >>
We analyze recent crustal movements, based on data of GPS measurements on the Amurian Plate and its margins. Most of the velocities were borrowed from scientific publications. Also, our new and updated data of periodic and permanent GPS observations are presented. A continuous field of strain rates has been constructed using the combined field of movement velocities. Dilation rates and the directions and values of the main strain axes have been calculated. We have made a quantitative estimation of the maximum shear rates and their directions. Zones of background deformations in the inner part of the Amurian Plate have been revealed along with high-strain zones. Zones with intense tectonic activity, corresponding to areas of reduced lithosphere, often show manifestations of Late Cenozoic volcanism. Part of them can be interpreted as the present-day boundaries of intracontinental geoblocks and small lithospheric plates.



9.
PATTERNS OF STRESS DROP IN EARTHQUAKES OF THE NORTHERN TIEN SHAN

N.A. Sycheva1, L.M. Bogomolov2
1Science Station of the Russian Academy of Sciences, Bishkek, 720049, Kyrgyzstan
2Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, ul. Nauki 1b, Yuzhno-Sakhalinsk, 693022, Russia
Keywords: Sesimogram, earthquake, source, spectrum, scalar seismic moment, source radius, stress drop, earthquake mechanism

Abstract >>
Source parameters of local earthquakes that occurred between 1998 and 2012 within the Kyrgyz seismological network (KNET) are used to study the patterns of stress drop in the Northern Tien Shan. The dynamic parameters of source radius r , the seismic moment M 0, and the stress drop Δσ are estimated for eighty seven M = 3.0-5.5 ( K = 9.5-13.7) events, which make up 86 % of earthquakes with this magnitude (99) for the period of observations. Earthquake mechanisms are determined either from P -wave arrivals (66 events) or by inversion (14 events). The distribution of earthquake mechanisms with the maximum (14 events) and minimum (14 events) stress drop shows that the amount of released stress correlates with slip geometry and revere-slip events contribute the most into the stress drop in the area. The spatial distribution of events with Δσ > 0.9 MPa is compared with maps of kinematic parameters (Lodé-Nadaì coefficient or stress ratio, μσ, and stress-strain line slope, ω) based on average strain tensors according to the complete earthquake catalog for the Northern Tien Shan (1056 events for 1998-2012). The two sets of source parameters ( r , M 0, Δσ and μσ, ω) correlate within the eastern Kyrgyz Range and the Karamoinok and Syndyk ranges.



10.
RANDOM AND COOPERATIVE ACCUMULATION OF INTRA- AND INTERGRANULAR DEFECTS IN GRANITE SUBJECT TO HIGH-TEMPERATURE IMPACT FRACTURE

I.P. Shcherbakov, A.E. Chmel
Ioffe Institute, Fracture Physics Department, Russian Academy of Sciences, ul. Politecknicheskaya 26, 194021, St. Petersburg, Russia
Keywords: Granite, quartz, impact fracture, acoustic emission, temperature dependence

Abstract >>
Acoustic emission (AE) from laboratory samples of coarse-grained granite hit by a dropped weight at temperatures from 20 to 500 C is recorded within a frequency range of 80 kHz-4 MHz. The time series of AE signals bear information on the size of primary defects, since the AE frequency is proportional to the growth rate of microcracks and inversely proportional to their lengths. According to AE data obtained in this study, impact fracture of granite produces cracks at grain boundaries at temperatures below 400 C and additional defects inside grains at 400 C and higher. The reason is that overheated water-vapor inclusions increase pressure in the grain interior, which affects the mechanic behavior of granite.