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Russian Geology and Geophysics

2013 year, number 2

1.
THE RIFT ORIGIN OF THE VILYUI BASIN (East Siberia), FROM RECONSTRUCTIONS OF SEDIMENTATION AND MECHANICAL MATHEMATICAL MODELING

O.P. Polyanskii, A.V. Prokopev, A.V. Babichev, S.N. Korobeinikov, V.V. Reverdatto
Keywords: Sedimentary basin, rift, subsidence, numerical simulation, backstripping analysis, extension, deformations
Pages: 121-137

Abstract >>
Results of modeling of the formation of the Vilyui sedimentary basin are presented. We combine backstripping reconstructions of sedimentation and thermal regime during the subsidence with a numerical simulation based on the deformable solid mechanics. Lithological data and stratigraphic sections were used to strip the sedimentary beds successively and calculate the depth of the stratigraphic units during the sedimentation. It is the first time that the evolution of sedimentation which is nonuniform over the basin area has been analyzed for the Vilyui basin. The rift origin of the basin is proven. We estimate the spatial distribution of the parameters of crustal and mantle lithosphere extension as well as expansion due to dike intrusion. According to the reconstructions, the type of subsidence curves for the sedimentary rocks of the basin depends on the tectonic regime of sedimentation in individual basins. The backstripping analysis revealed two stages of extension (sediments 45 km thick) and a foreland stage (sediments >2 km thick). With the two-layered lithosphere model, we conclude that the subcrustal layer underwent predominant extension (by a factor of 1.22.0 vs. 1.11.4 in the crust). The goal of numerical experiments is to demonstrate that deep troughs can form in the continental crust under its finite extension. Unlike the oceanic rifting models, this modeling shows no complete destruction or rupture of the continental crust during the extension. The 2D numerical simulation shows the possibility of considerable basement subsidence near the central axis and explains why mafic dikes are concentrated on the basin periphery.



2.
RECONSTRUCTING THE STAGES OF OROGENY AROUND THE JUNGGAR BASIN FROM THE LITHOSTRATIGRAPHY OF LATE PALEOZOIC, MESOZOIC, AND CENOZOIC SEDIMENTS

I.S. Novikov
Keywords: Orogenic chronology, paleogeography, Junggar basin, Northwest China, Xinjiang
Pages: 138-152

Abstract >>
The Junggar basin contains an almost continuous section of Late CarboniferousQuaternary terrigenous sedimentary rocks. The maximum thicknesses of the stratigraphic units constituting the basin cover make up a total of 23 km, and the basement under the deepest part of the basin is localized at a depth of 18 km. Both the folded framing and the basin edges have undergone uplifting and erosion during recent activity. These processes have exposed all the structural stages of the basin cover. Considering the completeness and detailed stratigraphic division of the section, we can determine the exact geologic age of intense mountain growth and erosion periods as well as estimate the age of orogeny periods by interpolating the stratigraphic ages. During the Permian orogeny, which included two stages (255265 and 275290 Ma), the Junggar, Zaisan, and TurpanHami basins made up a whole. During the Triassic orogeny (210230 Ma), the Junggar and TurpanHami basins became completely isolated from each other. During the Jurassic orogeny (135145 and 160200 Ma), the sedimentation took place within similar boundaries but over a smaller area. During the Cretaceous orogeny (6585 and 125135 Ma), the mountain structures formed mainly at the southern boundaries of the basin and along the KaramailiSaur line. The Junggar and Zaisan basins were separated at that time. The Early and Middle Paleogene were characterized by relative tectonic quiescence. The fifth orogenic stage began in the Oligocene. The recent activity consists of two main stages: Oligocene (2333 Ma) and NeogeneQuaternary (1.27.6 Ma to the present).



3.
HIGH-MAGNESIUM PICRITEBASALT ASSOCIATIONS OF THE TUNKA TERRANE ( BaikalHovsgol region) AS AN INDICATOR OF THE back-Arc BASIN SPREADING

S.I. Shkolnik, V.G. Belichenko, L.Z. Reznitskii
Keywords: Metavolcanics, picrites, basalts, geochemistry, back-arc spreading, Tunka terrane
Pages: 153-165

Abstract >>
High-Mg metabasalts and metapicrites discovered within the Urtagol Formation in the central zone of the Tunka bald mountains (East Sayan) are studied. In geochemistry the high-Mg metavolcanics are similar to subductional rocks. We have established that the Nb-rich recycled material of oceanic crust (RSC) was a source of elements for high-Ti metabasalts, and subductional fluid rich in LREE and Th relative to Nb was the source of these elements for high-Ti metapicrites. The enrichment of low-Ti metavolcanics, formed, probably, at the early stages of the basin opening, was due to the contamination of melt with continental-crust material. A comparison of the metavolcanics with nonmetamorphosed analogs is made, and some genesis aspects are considered. The results obtained led to the conclusion that the metavolcanics mark the paleospreading of the back-arc basin.



4.
THE TALAZHIN PLAGIODUNITETROCTOLITEANORTHOSITEGABBRO MASSIF ( East Sayan): PETROGEOCHEMISTRY AND ORE POTENTIAL

A.N. Yurichev, A.I. Chernyshov, E.G. Konnikov
Keywords: Layered massifs, plagiodunites, troctolites, petrology, ore mineralization
Pages: 166-180

Abstract >>
The petrology and ore potential of the Talazhin massif located in northwestern East Sayan are studied. The internal structure of the intrusion, the petrographic composition of its rocks, and their metallogenic, petrostructural, and petrogeochemical features are considered. The probable temperature and chemical composition of the parental magma of the pluton were computed using the KOMAGMAT-3.52 program on the modeling of equilibrium crystallization. The obtained data indicate that the Talazhin massif is a rhythmically layered plagiodunitetroctoliteanorthositegabbro intrusion formed from low-Ti high-alumina olivinebasalt melt. It is promising for CuNiPGE mineralization.



5.
SELF-CONSISTENT PRESSURE SCALES BASED ON THE EQUATIONS OF STATE FOR RUBY, DIAMOND, MgO, B2NaCl AS WELL AS Au, Pt, AND OTHER METALS TO 4 Mbar AND 3000 K

T.S. Sokolova, P.I. Dorogokupets, K.D. Litasov
Keywords: , , , , Ag, Al, Au, Cu, Mo, Nb, Pt, Ta, W, MgO, B2-NaCl
Pages: 181-199



6.
THE ROLE OF PRESSURE IN THERMOCATALYTIC PROCESSES IN THE SEDIMENTARY COMPLEX OF THE SOUTH CASPIAN BASIN

A.A. Feyzullayev
Keywords: Fluid overpressures, cracking, kerogen, oil, clay-mineral transformation, retardation, South Caspian basin
Pages: 200-205

Abstract >>
The role of overpressures in thermochemical processes in the South Caspian basin is considered. The studies, which take the world experience into account, suggest that the South Caspian basin (mainly its deep-water part), as well as other basins with abnormally high fluid pressures, is characterized by retarded kerogen and oil cracking and reaction of clay-mineral transformation. These processes can be periodically intensified by the development of diapirs and mud volcanoes, which are centers of pulsed hydrocarbon discharge from the system. The conclusion is made that deeply buried deposits in basins with fluid overpressure are promising for hydrocarbon pools.



7.
STRESS AND DEFORMATION OF THE EARTHS CRUST IN THE ALTAI-SAYAN MOUNTAINOUS AREA

Yu.L. Rebetsky, O.A. Kuchai, A.V. Marinin
Keywords: Tectonophysics, geodynamics, stresses, strains, faults, earthquake focal mechanisms, loading mechanisms
Pages: 206-222

Abstract >>
We present the results of tectonophysical reconstruction of natural stress of the Earths crust in the Altai-Sayan mountain region using cataclastic analysis of fault slips and seismic data on the focal mechanisms of earthquakes. This method allows one to obtain the parameters of the total stress tensor by invoking additional data: generalized experimental data on the brittle fracture of rocks, seismic data on the released stress of strong earthquakes, and data on the topography and density of rocks. The results of the tectonophysical reconstruction of stresses showed significant heterogeneity of the stress state, which is manifested not only in the variation of the strike and dip of the principal axes of the stress tensor, determining changes in the geodynamic regime of the Earths crust, but also in the close location of the regions of high and low isotropic tectonic pressure in relation to the lithostatic pressure. The variance of the ratio of tectonic pressure to lithostatic pressure is in the range of 0.591.31, with an average value for the region close to unity. This paper discusses internal or external mechanisms capable of generating the stress field obtained by the tectonophysical reconstruction.



8.
ACCELERATION RESPONSE SPECTRA FOR THE EARTHQUAKES OF THE SOUTHWESTERN FLANK OF THE BAIKAL RIFT ZONE

A.F. Drennov, V.I. Dzhurik, S.P. Serebrennikov, E.V. Bryzhak, N.N. Drennova
Keywords: Acceleration response spectra, strong earthquakes, sense of fault motion, Baikal Rift Zone
Pages: 223-230

Abstract >>
The acceleration response spectra of earthquakes with M = 4.06.5 in the southwestern part of the Baikal Rift Zone have been studied. The absorption properties of the medium and the attenuation of seismic signals in the study region were determined. Average acceleration response spectra were obtained for regional earthquakes. A comparative analysis of the acceleration response spectra was made for earthquakes focal mechanisms with different senses of motions: reverse faults, reverse slip, strike slip, and oblique slip. The effect of the sense of fault motion in the seismic source on acceleration response spectra was determined.



9.
TIME CORRELATION OF CRACK FORMATION DURING IMPACT FRACTURING OF ROCKS

I.P. Shcherbakov, V.S. Kuksenko, A.E. Chmel
Keywords: Granite, dynamic fracturing, acoustic emission, fractoluminescence, waiting time
Pages: 231-236

Abstract >>
Samples of marble and granite with different grain sizes were subjected to impact fracturing under laboratory conditions. The acoustic-emission (AE) signals generated by growing cracks were recorded at 10 ns intervals. Synchronically, the fractoluminescence (FL) resulting from the breakage of interatomic bonds on the sample surface was recorded. The duration of the intervals between the AE signals was shown to be a power-low function typical of correlated (self-similar) processes. However, the FL signals did not follow this law, because the duration of free-radical formation is much shorter than the intervals at which they appear when chemical bonds break down. The AE data indicate that new cracks appear more often in materials with a smaller grain size.



10.
STONELEY WAVES, RADIAL WAVES, AND METHOD OF MEASURING PERMEABILITY AND ELECTROACOUSTIC CONSTANT OF SATURATED POROUS MEDIA

V.N. Dorovsky, Yu.V. Perepechko, A.I. Fedorov
Keywords: Permeability, saturated porous media, acoustic waves, radial oscillations, Stoneley waves, electroacoustic constant
Pages: 237-245

Abstract >>
A two-mode method of measuring permeability and electroacoustic constant in the course of borehole logging is considered. The first mode is the Stoneley wave with its electroacoustic ratio; the second mode is the radial wave in the formation around the borehole with the electric field it generates. The radial wave enables one to measure the electroacoustic constant and the Stoneley wave, the electroacoustic ratio, linearly dependent on permeability. Using these measurements jointly enables one to find permeability of the porous medium. All formation evaluation can be reduced to an additional measurement of electric conductivity.