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Russian Geology and Geophysics

2009 year, number 1

1.
Permo-Triassic volcanics of the Koltogory-Urengoi rift of the West Siberian geosyneclise

S.V. Saraeva, T.P. Baturinaa, V.A. Ponomarchuk b , A.V. Travin b
a Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Volcanism; geochemistry; geodynamics; Permo-Triassic; West Siberian geosyneclise
Pages: 1-14

Abstract >>
The lithologic composition of basalts from the most complex sections of the Koltogory-Urengoi Rift is considered, and their 40Ar/39Ar ages are given: basalts from the lower section of Nikol'skaya BH-1 (Bergamak Formation) - 272.9 ± 10.5 and 249.5 ± 3.0 Ma, basalts from the uppermost section (Voinov Formation) - 247.5 ± 2.9 Ma, and basalts from the lower section of Tyumenskaya SDB-6 (Korotchaevo Formation) - 251.2 ± 2.0 Ma. According to these and the paleomagnetic data, trap magmatism began in the Koltogory-Urengoi Rift in the Permian and ended in the Early Triassic, whereas the paleontological data suggest its beginning in the Early Triassic and its termination in the late Middle Triassic.
In Tyumenskaya SDB-6 we have recognized both low-K tholeiitic and medium- to high-K subalkalic and calc-alkalic basalts, which form large alternating packets up to 480 m thick. This section is juxtaposed to the anomalous sections of the Siberian Platform trap formation near the margins of the Tunguska syneclise. The section of Nikol'skaya BH-1 is composed mainly of medium- and high-K subalkaline basalts with scarce flows of low-K ones. The low-K basalts differ from the medium- and high-K varieties in having lower contents of TiO2, P2O5, Ba, Rb, Th, and ΣLREE.
The Tyumenskaya SDB-6 basalts are characterized by paleohypergene alterations, up to the development of more than five levels of alumina-ferruginous cuirasses, as well as superposed chloritization, sericitization (hydromication), carbonatization, zeolitization, silicification, and epidotization, whereas the Nikol'skaya BH-1 basalts are subjected mainly to carbonatization, chloritization, and hydromication.
We have concluded that the existence of a vast mega-arch above the superplume within the West Siberian geosyneclise in the Permo-Triassic was complicated by the Koltogory-Urengoi Rift. The Triassic rift deposits are both continental and marine sediments (sandstones and siltstones with glauconite, coccolith oozes, spherulitic lavas, and hyaloclastites). The basic volcanism within the rift showed the features of both rift and flood basalts as well as E-MORB.
																								



2.
Paleoarchean tonalite-trondhjemite complex in the northwestern part of the Sharyzhalgai uplift (southwestern Siberian craton): results of U-Pb and Sm-Nd study

O.M. Turkina a,b , N.G. Berezhnaya c , A.N. Larionov c , E.N. Lepekhina c , S.L. Presnyakov c , T.E. Saltykova c
a Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Novosibirsk State University, 2 ul. Pirogova, Novosibirsk, 630090, Russia
c All-Russian Research Geological Institute, 74 Srednii prosp., St. Petersburg, 199106, Russia
Keywords: Paleoarchean; Siberian craton; Sharyzhalgai uplift; tonalities; trondhjemites; U-Pb age; Sm-Nd isotope geochemistry; petrogenesis
Pages: 15-28

Abstract >>
In the northwestern part of the Sharyzhalgai uplift of the Siberian craton (Bulun block), the earliest sialic crust (grey-gneiss complex) is composed of plagiogneisses, their migmatized varieties, and subordinate plagiogranitoids. The petrochemical, trace-element, and Sm-Nd isotope compositions of rocks were studied, and U-Pb dating of zircons (SHRIMP II) was performed. Plagiogneisses and plagiogranitoids of trondhjemite and, more seldom, tonalite compositions are predominant; their compositions are typical of rocks of Archean tonalite-trondhjemite-granodiorite (TTG) complexes (Al2O3 ≥ 15%, Mg# = 28-38, (La/Yb) n = 23-66, Sr/Y = 27-135, Eu/Eu* = 0.7-1.1). Plagiogneisses of meta-andesite-rhyodacite association are subordinate (SiO2 = 59-69%, (La/Yb) n = 7-32, Sr/Y = 11-24, Eu/Eu* = 0.5-0.7). Cathodoluminescent study of zircons revealed
																								



3.
Rare-earth elements as indicators of ore sources and the degree of differentiation and ore potential of rare-metal granite intrusions (eastern Transbaikalia)

V.D. Kozlov
Institute of Geochemistry, Siberian Branch of the RAS, 1a ul. Favorskogo, Irkutsk, 664033, Russia
Keywords: Rare-earth elements; magmatic differentiation; rare-metal granites; granitophile trace elements; rare-metal mineralization; ore potential
Pages: 29-42

Abstract >>
The meteoritic-material-normalized REE patterns of rare-metal granite intrusions of the ore-bearing Kukul'bei complex (J2-J3), eastern Transbaikalia, were studied. It is shown that the intrusions were initially enriched in granitophile volatiles and trace elements (rare metals), i.e., this phenomenon is not related to the differentiation of their parental magma chambers. On the differentiation of the Kukul'bei rare-metal intrusions, the REE contents decrease in passing from granites of the main intrusive phase (MP) to late leucocratic differentiates (muscovite and amazonite granites), the differentiates become more enriched in granitophile elements, and their rare-metal contents drastically increase as compared with the MP granites. The ore-bearing bodies of muscovite and amazonite granites have extremely low REE contents and the highest contents of granitophile (including ore-forming) elements.
The REE patterns of the Kukul'bei intrusive differentiates are not universal among rare-metal intrusions. By the example of highly ore-bearing rare-metal granite intrusions of the Erzgebirge, Central Europe, it has been established that their late deep-seated differentiates (ultrarare-metal lithionite-zinnwaldite Li-F-granites) accompanied by highly productive Sn-W mineralization concentrate both granitophile elements and REE (particularly HREE). Among the studied Transbaikalian rare-metal intrusions of the Kukul'bei complex, only the differentiates of the most ore-bearing Sherlovaya Gora intrusive system belong to the above type. The analysis of the REE patterns of the Kukul'bei granites confirmed the earlier conclusions on the low ore potential of the rare-metal mineralization of the studied intrusive complex.
																								



4.
Two stages of high-pressure metamorphism in the Main Uralian Fault area (northern Urals)

G.A. Petrova, Yu.L. Ronkin b , N.V. Popov c , N.I. Tristan a , P.S. Kozlov b
a Uralian Geological-Survey Expedition Joint-Stock Company, 55 ul. Vainera, Yekaterinburg, 620144, Russia
b Institute of Geology and Geochemistry, Uralian Branch of the RAS, 7 Pochtovyi per., Yekaterinburg, 620151, Russia
c Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: High-pressure metamorphism; Main Uralian Fault; Sm-Nd isochrone age
Pages: 43-45

Abstract >>
Metamorphism in the northern sector of the Main Uralian Fault (MUF) area, northern Urals, is considered by the example of the Salatim glaucophane-schist and Belokamenka kyanite-staurolite complexes. New isotope-geochronological dates for metamorphic rocks of the MUF area are presented. The obtained data evidence the existence of two metamorphic events, of Early and Late Devonian ages, which apparently correspond to the wedging-up of subduction paleozones.
																								



5.
Ultrabroadband electromagnetic wave propagation in hydrocarbon reservoirs in the presence of an oil-water interface

M.I. Epov a , V.L. Mironov b , S.A. Komarov b , K.V. Muzalevskii c
a Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Physics, Siberian Branch of the RAS, 50/38, Akademgorodok, Krasnoyarsk, 660036, Russia
c Altai State University, 61 ul. Lenina, Barnaul, 656049, Russia
Keywords: Horizontal well; fluid-saturated formation; complex permittivity; dispersive mixtures; refractive dielectric model; broadband pulse; Green's function; simulation
Pages: 46-52

Abstract >>
Numerical experiments are applied to simulate propagation of broadband pulses which are transmitted by an electric dipole and travel in a uniform oil-bearing formation or in a layered reservoir with an oil-water interface. We calculate the frequency responses of the oil- and water-saturated layers as low-frequency filters for the propagating waves and find the respective cutoff frequencies. Attenuation rates are analyzed in the cases of incident nanosecond and picosecond pulses in uniform oil-bearing formations and those reflected from the oil-water interface. The low frequency filtering of pulses is investigated in terms of its effect on wave energy attenuation during propagation in oil-bearing rocks.
																								



6.
A new method of controlled-source frequency induction soundings

R.B. Zhuravleva, D.G. Mironov
Institute of Geophysics, Ural Branch of the RAS, 100 ul. Amundsena, Yekaterinburg, 620016, Russia
Keywords: Subsurface structure; information parameter; frequency induction sounding; field frequency; separation; resistivity; resolution
Pages: 53-56

Abstract >>
We suggest a new inversion method for frequency induction data implying the use of a new parameter, which has a simple analytical form in the case of a uniform subsurface. The new parameter is found from induction numbers measured in the field of a vertical magnetic dipole or a vertical magnetic dipole combined either with a horizontal electrical dipole or with a horizontal magnetic dipole. Compared with the classical methods, the new technique provides better resolved resistivity curves and faithful images of the subsurface at higher frequencies and smaller transmitter-receiver separations. The inversion algorithm is applied to amplitude and amplitude-phase data and provides reliable depth assignment of the detected resistivity layers in the latter case.
																								



7.
Paleomagnetism of granites from the Angara-Kan basement inlier, Siberian craton

A.N. Didenko a,b , I.K. Kozakov c , A.V. Dvorova b
a Kosygin Institute of Tectonics and Geophysics, Far Eastern Branch of the RAS, 65 ul. Kim Yu Chena, Khabarovsk, 680000, Russia
b Geological Institute, Russian Academy of Sciences, 7 Pyzhevsky per., Moscow, 119017, Russia
c Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, 21 nab. Makarova, St. Petersburg, 199034, Russia
Keywords: Paleoproterozoic; paleomagnetic pole; Siberian craton
Pages: 57-62

Abstract >>
We report a new paleomagnetic determination of Paleoproterozoic rocks from the Siberian craton which showed a positive baked contact test and a stable age of the high-temperature NRM component. The mean paleomagnetic pole of Siberia for ~1730 Ma located at 42.9
																								



8.
A macroseismic study of the Taldy-Sai caravanserai in the Kara-Bura River valley (Talas basin, Kyrgyzstan)

A.M. Korjenkov a , K.Sh. Tabaldiev b , Al.V. Bobrovskii c , Ar.V. Bobrovskii a , E.M. Mamyrov a , L.A. Orlova d
a Institute of Seismology, National Academy of Sciences of Kyrgyzstan, 52/1 Asanbai, Bishkek, 720060, Kyrgyzstan
b Manas Kyrgyz-Turkey University, 135 Dzhal, Bishkek, 720044, Kyrgyzstan
c National Mapping & Geodetic Surveys of Kyrgyzstan, 107 ul. Kievskaya, Bishkek, 720001, Kyrgyzstan
d Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Archeoseismology; earthquake-induced damage to buildings; damage patterns; Talas valley, Kyrgyzstan
Pages: 63-70

Abstract >>
We report a macroseismic study of a ruined medieval building, a small caravanserai located along the caravan way from the Talas valley to the Chatkal and Fergana valleys in Kyrgyzstan. The ruins document several events in which the caravanserai was destroyed, apparently during earthquakes, and was rebuilt or repaired. The earliest earthquake occurred soon after the building was put up, about 400 years ago, according to radiocarbon dating of charcoal, and another event shook the area between 400 and 50 years BP. After being damaged in the ultimate earthquake, in the middle of the 20th century, the building was eventually abandoned.