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Russian Geology and Geophysics

2002 year, number 9

1.
A NEW REFERENCE SECTION FOR THE UPPER JURASSIC AND CALLOVIAN IN NORTHERN WEST SIBERIA

A. L. Beizel', Yu. N. Zanin, A. G. Zamirailova, V. I. Il'ina, N. K. Lebedeva, L. K. Levchuk, M. A. Levchuk, S. V. Meledina, B. L. Nikitenko, B. N. Shurygin, and P. A. Yan
Keywords: Upper Jurassic and Callovian deposits, stratigraphy, lithology, ammonites, bivalves, microfauna, spore and pollen, dinocysts
Pages: 811-825

Abstract >>
The section of Zapadno-Purpeiskaya BH-710, drilled in the central part of the plate, is one of the reference sections of the Upper Jurassic in northern West Siberia. This section is represented by a succession of formations most typical of this range in West Siberia: Vasyugan, Georgievka, and Bazhenov. The rock lithology was examined in detail. The section was paleontologically characterized using a complete range of fossils: ammonites, bivalves, microfauna, dinocysts, spore, and pollen. On this basis the section was subdivided biostratigraphically. Logging data have been analyzed. Some new stratigraphic results have been obtained. The middle part of the Callovian (uppermost Lower Callovian, Middle Callovian and, partly, Upper Callovian) in the studied section is severely reduced to absent. The ammonites Indosphinctes (Elatmites) mokschaensis (Sas.) have been found in West Siberia for the first time. This species is widespread in the Middle (and partly Upper) Callovian of the Russian Platform. The Middle-Upper Volgian part of the Bazhenov Formation is much reduced in thickness. It has been established that the largest (upper) part (about two thirds) of the Bazhenov Formation in this section is of Berriasian age. The interval between the ammonite-based uppermost beds of the Lower Berriasian and the lowermost beds of the Lower Valanginian is about 12 m. About a half of them is occupied by the upper part of the Bazhenov Formation overlapped by the Sortym Formation.



2.
ESTIMATION OF HF CONTENTS IN MAGMATOGENE FLUIDS OF PORPHYRY Cu-Mo ORE-MAGMATIC SYSTEMS (Siberia, Mongolia)

V. I. Sotnikov, A. N. Berzina, A. P. Berzina, V. O. Gimon, and V. Yu. Kiseleva
Keywords: Porphyry Cu-Mo deposits, magmatogene fluids, concentration of HF, sources of fluorine, Siberia, Mongolia
Pages: 837-846

Abstract >>
From results of microprobe analysis and experimental data on biotite systems of ore-bearing porphyry complexes (stocks, dikes) and the host granitoids (massifs), we have calculated concentrations of HF in magmatogene fluids coexisting with biotite. Porphyry complexes of Cu-Mo deposits of Siberia and Mongolia are characterized by low concentrations of HF (MHF): from 0.0153 to 0.0024 mole/dm3 at T = 800-700 oC. The MHF of the deposits decreases in the sequence: Sora-Vykhodnoe-Zhireken, Aksug-Erdenetuin-Obo-Shakhtama. This sequence (except for the Shakhtama deposit) is to a certain extent correlated with the silica content of ore-bearing porphyries, intensity of potassic metasomatism, and Cu/Mo in ores. We have found no correlation of MHF with (87Sr/86Sr)0 of porphyries, abundance of mineralization, and contents of ore-forming components. The ore-bearing porphyries and more ancient host granitoids (except for the large Erdenetuin-Obo deposit and Vykhodnoe ore occurrence) differ slightly in MHF. Therefore, the elevated activity of HF in porphyry Cu-Mo ore-magmatic systems is related not only to the concentration of F in magmas but also to the evolution of porphyry melts in more open settings. The great spread in (87Sr/86Sr)0 values of ore-bearing porphyry complexes at different deposits (from 0.70393 to 0.70774) suggests mantle-crustal sources of fluorine.



3.
ELVANS OF CORNWALL (England) AND SOUTHERN SIBERIA AS SUBVOLCANIC COUNTERPARTS OF SUBALKALIC RARE METAL GRANITES

V. S. Antipin, C. Halls, M. A. Mitichkin, P. Scott, and A. N. Kuznetsov
Keywords: Elvans and rare-metal granites, geochemistry, magmatism, petrology, basalts and monzonitoids, dike belt, subvolcanic rock, isotope-geochemical study
Pages: 847-857

Abstract >>
Elvans are known from several rare metal provinces, where they are spatially and genetically closely related to subalkalic rare-metal granites. Elvan magmatism manifests itself at the final stage of the evolution of lower-crustal granitoid magma chambers. Elvans are produced by differentiation of a subalkalic granitoid magma. Occurrence of elvans in zones of deep-seated faults and dike belts, where basite and monzonitoid magmatism is expressed, as well as isotope-geochemical data suggest that the elvan formation was much affected by a subcrustal fluid enriched in specific rare elements.



4.
ULTRAMAFIC ROCKS OF RAKOVAYA BAY (Eastern Kamchatka): COMPOSITION AND GEODYNAMIC CLASSIFICATION

A. B. Osipenko and G. I. Anosov
Keywords: Ultramafic rocks, ophiolites, mineralogy, geochemistry, paleogeodynamics, Eastern Kamchatka
Pages: 858-872

Abstract >>
We present results of detailed mineralogical and geochemical investigations of peridotites from allochthonous plate in Rakovaya Bay (the north of Avachinskaya Bay, Eastern Kamchatka). In geologic position and composition the studied rocks are much similar to ultramafic rocks of other massifs of the East Kamchatkan ophiolite belt and <%-2>are referred to as restite peridotites of the so-called suprasubductional type transformed by multistage metamorphism. It is suggested that peridotites of Rakovaya Bay along with ultramafic rocks of the Ganal'sky Ridge and ultrabasic xenoliths of the Avachinsky Volcano form a linear NW-oriented zone, which spatially coincides with the Avacha-Kolpakova zone of structural deformations and is the southern margin of the area of occurrence of ophiolite-type ultramafic rocks in Eastern Kamchatka.



5.
LABORATORY SEISMIC MODELING OF A MEDIUM CONTAINING FLUID-SATURATED SANDSTONE

A. M. Verkhovskii
Keywords: Physical modeling, fluid-saturated sandstone
Pages: 873-881

Abstract >>
The paper addresses modeling of sandstone as a mixture of sand grains with predetermined size distribution, modal diameter, and sorting coefficient of grains and content of fine-grained (viscous) component. Sandstone is considered a granular medium whose properties are analyzed in terms of controlling processes and modeling suitability. The behavior of grain contacts is the most difficult point of modeling.
The suggested 2D (sheet) model simulates a medium containing a layer of fluid-saturated sandstone. The model includes acoustic and filtration properties of grain contacts with flat surfaces. Vacuum fluid saturation may account for various types of natural settings, namely, oil plus bound water (oil reservoir), gas plus bound water (gas reservoir), and water alone (water reservoir).



6.
CRACKED SOLID GEOMETRY AND PARAMETRIC RESONANCE

B. P. Sibiryakov
Keywords: Pore geometry, specific surface area, instability, resonance
Pages: 882-887

Abstract >>
Resonance phenomena are often observed in seismology and seismic exploration: vibration applied to oil wells, earthquakes caused by periodic oscillations of hydropower stations, crust movements associated with Moon rotation, or motions of the Earth's surface felt in regions of active petroleum production. These phenomena have a surprisingly poor theoretical background in geophysics, though parametric resonance is well known in physics. The reason may be that wave phenomena in rocks are simulated in geophysics in the context of continuum media that lack internal geometry and, hence, characteristic sizes of structures related to the specific surface area. However, resonance phenomena fraught with natural and technical risk can be theoretically investigated in terms of a model containing specific surface area of cracks with a length-inverse dimension.



7.
To the 70th birthday of Al'girdas-Zenonas Stanislovo Dagis


Pages: 888