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Russian Geology and Geophysics

2005 year, number 11

1.
PALEOMAGNETISM OF THE PERMIAN-TRIASSIC TRAPS FROM THE KUZNETSK BASIN, SOUTHERN SIBERIA

A.Yu. Kazansky, D.V. Metelkin, V.Yu. Bragin, and L.V. Kungurtsev
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Trap formation, Permian-Triassic, paleomagnetism, intraplate displacement, Kuznetsk Basin
Pages: 1089-1102

Abstract >>
In this paper we generalize the data obtained for the Kuznetsk Basin traps studied over many years. A rich collection of samples from the Permian and Triassic igneous/sedimentary succession of the Kuznetsk Basin was analyzed. As a result, directions of characteristic remanent magnetization have been established ( Ds = 227.1, Is = -64.3, α95 = 2.8). Also, the paleomagnetic pole has been located accurately enough to be used in paleotectonic reconstructions. The Permian-Triassic age of the characteristic component of magnetization has been confirmed by fold and baked-contact tests. Comparative analysis of the magnetic zoning record in the sections of traps of the Kuznetsk Basin, northern Siberian Platform and West Siberian Plate shows that the processes of intraplate magmatism were mutually related in these areas about the time of the Permian-Triassic transition. Systematization of the obtained and available paleomagnetic data shows that the trap magmatism in the Kuznetsk Basin, as compared with the rest of Siberia, was an extremely short-term event. The entire section corresponds to the initial stage of the intraplate magmatic activity in the Siberian region, with their formation lasting no more than 1 Myr. The position of the calculated paleomagnetic pole (PLat = 60.0, PLong = 172.7, α95 = 4.0) and the orientation of the Permo-Triassic latitudes of the Kuznetsk Basin have a considerable angular deviation from those of the Siberian Platform (PLat = 49.0, PLong = 151.6, α95 = 5.0). The angular distance makes about 24
																								



2.
PETROSTRUCTURAL SIGNATURE OF OLIVINES IN ULTRAMAFIC ROCKS OF THE PARAMSKY AND SHAMANSKY MASSIFS (Baikal-Muya ophiolite belt)

A.I. Chernyshov
Tomsk State University, 36 ul. Lenina, Tomsk, 634050, Russia
Keywords: Ophiolites, ultramafic rocks, olivine, plastic deformation, petrofabric, thermodynamic conditions, dislocations, Baikal-Muya belt
Pages: 1103-1114

Abstract >>
The olivines in dunites and harzburgites of ophiolite massifs in the Baikal-Muya belt are characterized by a great diversity of deformations with a regular change of microstructural types: protogranular, mesogranular, porphyroclastic, porphyrolath, mosaic, mosaic-lath, and parquet-like. Petrofabrics of the petro- and mesogranular types have been formed by the translation slip and static annealing recrystallization at 1100-1300
																								



3.
CAMBRIAN GRANODIORITES AND THEIR PALEOWEATHERING PRODUCTS IN THE SOUTHEAST OF THE WEST SIBERIAN GEOSYNECLISE: PETROGRAPHY, GEOCHEMISTRY, AND 40Ar/39Ar AGE

S.V. Saraev and V.A. Ponomarchuk
United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: West Siberian geosyneclise, granodiorites, absolute age, Cambrian, weathering
Pages: 1115-1120

Abstract >>
Using the 40Ar/39Ar method, an Early Cambrian age has been established for granodiorites stripped in the bottom-hole zone (4824-5005 m) of Vezdekhodnaya BH-4 (Tomsk Region) in the southeast of the West Siberian geosyneclise. Primitive crust of weathering is developed on the granodiorites. The rocks are overlain by gritstones of sedimentary nature. The results obtained suggest a short time gap between the intrusion of the granodiorites into volcanosedimentary strata and the first effusion of the overlying submarine basalts.
																								



4.
THE AGE AND GEODYNAMIC INTERPRETATION OF THE KITOI GRANITOID COMPLEX (southern Siberian craton)

D.P. Gladkochub, T.V. Donskaya, A.M. Mazukabzov, E.B. Sal'nikova*, E.V. Sklyarov, and S.Z. Yakovleva*
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
* Institute of the Precambrian Geology and Geochronology, Russian Academy of Sciences,
2 nab. Makarova, St. Petersburg, 199034, Russia
Keywords: Granitoids, terrane, supercontinent, Late Archean, Siberian craton
Pages: 1121-1133

Abstract >>
Study was given to granitoids of the Kitoi complex on the southern flank of the Siberian craton (Sharyzhalgai uplift). The granitoids are regarded as syntectonic in accordance with their regional occurrence, geology, and structure. Their U-Pb zircon age is 2532 ± 12 Ma. Petrological, geochemical, and isotopic data obtained suggest that the Kitoi granitoids might have been produced from the enclosing metamorphosed sedimentary rocks. The intrusion of these granitoids proceeded synchronously with the formation of the Late Archean Urik-Kitoi collision zone, which originated during the accretion of the Irkut and Oka superterranes of the Sharyzhalgai uplift. Granitoids of the Kitoi complex and coeval granulites of the Urik-Kitoi collision zone are indicators of Late Archean collision processes running within the Sharyzhalgai uplift. These collision and accretion processes correlate well with similar events that took place in the Aldan Shield and in some ancient cratons. On a global scale, these events proceeded during the formation of the Late Archean Pangea 0 supercontinent (Arctic).
																								



5.
PALEOCARPOLOGY AND PROBLEMS OF THE PALEOGENE STRATIGRAPHY OF WEST SIBERIA

V.P. Nikitin
Novosibirskgeologiya Enterprise, 28 ul. Romanova, Novosibirsk, 630099, Russia
Keywords: Eocene, Oligocene, stage, seed complexes, floristic levels, West Siberia
Pages: 1134-1140

Abstract >>
By the example of West Siberia, it is shown that paleocarpology permits fractional division of continental Cenozoic strata in closed areas, impossible with other paleontological methods. Ten biostratigraphic zones have been recognized in the studied Upper Lutetian-Aquitanian stratigraphic section.
																								



6.
STRUCTURE OF SEDIMENTARY COVER AND BASEMENT BENEATH THE SOUTH BASIN OF LAKE BAIKAL INFERRED FROM SEISMIC PROFILING

V.D. Suvorov and Z.R. Mishen'kina
Institute of Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Seismic structure, velocity, sediment, Lake Baikal
Pages: 1141-1149

Abstract >>
Structure of the deposits and basement beneath the South basin of Lake Baikal is investigated down to a depth of 14 km on a profile about 100 km long. Ray tracing modeling of refracted and reflected waves is applied. A discrepancy between the observed and calculated wave traveltimes does not exceed 0.05-0.1 s for the parameters of cross section. In addition, the reliability of the sedimentary cover structure is confirmed by similar synthetic and observed record sections. Four layers with individual characteristics are allocated, divided by seismic boundaries with rather sharp differences of velocity. Velocity changes with depth on the given profile are similar to results of seismic observations in the Selenga depression, in deposits of the West Siberian Plate, Siberian craton and Vilyui basin. It is possible to assume that the sedimentary cover up to 10-12 km thick hosts not only Cenozoic and Mesozoic but also Paleozoic rocks. Therefore it is possible that the age of the South basin of Lake Baikal is more ancient than the Cenozoic-Mesozoic.
																								



7.
SPACE SENSITIVITY OF RELATIVE PARAMETERS IN HIGH-FREQUENCY ELECTROMAGNETIC LOGGING

V.N. Glinskikh and M.I. Epov
Institute of Geophysics, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Pseudogeometric factor, approximate approach, phase difference, relative amplitude, high-frequency electromagnetic sounding
Pages: 1150-1157

Abstract >>
The study develops methods for approximate simulation of high-frequency relative parameters in models of 2D conducting media using the pseudogeometrical factor approach. Linear representation of magnetic field is applied to obtain equations of pseudogeometrical factors for relative amplitude and phase difference which define conductivity and permittivity dependences of signals. Modeling the contributions of separate zones of the subsurface to the signals allowed inferences on the down-well resolution of sounding. The new algorithms for the integral contributions and pseudogeometrical factors proved to be efficient tools in instrument design and data processing.
																								



8.
STRAIN WAVES IN THE EARTH: THEORY, FIELD DATA, AND MODELS

V.G. Bykov
Kosygin Institute of Tectonics and Geophysics, Far Eastern Branch of the RAS,
65 ul. Kim Yu Chen, Khabarovsk, 680000, Russia
Keywords: Strain wave, tectonic wave, generation mechanism, earthquake migration, seismology
Pages: 1158-1170

Abstract >>
The presented overview traces the development of the strain wave theory over the past 35 years. The study includes classification of strain waves reported in the literature and analysis of the relevant terminology. Twenty five basic terms actually denote various features of the deformation process expressed at different scales. The terms are synthesized in tables that display the original definitions and interpretations, the forms of manifestation of strain waves in nature and recording methods, as well as velocities, sources, and hypothetical mechanisms of generation of these waves. The strain wave theory can provide a physical background for explaining the driving mechanisms of seismic migration.