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Russian Geology and Geophysics

2012 year, number 8

1.
THE ALKALINE AND CARBONATITIC ROCKS OF GORNY ALTAI ( Edel'veis omplex ) AS INDICATORS OF EARLY PALEOZOIC PLUME MAGMATISM IN THE CENTRAL ASIAN FOLD BELT

V.V. Vrublevskiia, V.I. Krupchatnikova, A.E. Izokhb, and I.F. Gertnera
aTomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
bV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Alkaline magmatism, carbonatites, mantle plume, Central Asian Fold Belt
Pages: 721-735

Abstract >>
The minor intrusions of the Edel'veis alkaline-carbonatite complex are bounded by the spurs of the North Chuya Ridge in southeastern Gorny Altai. According to Ar-Ar isotope data, the complex formed in the Middle Cambrian (~507 Ma). All of its components (alkali clinopyroxenite-melanogabbro-alkali syenite + Ca-carbonatite) occur in only one pluton. Silicate igneous rocks are equivalent in silica content and alkalinity to potassic alkaline and subalkalic mafic rocks. Apatite-phlogopitic Ca-carbonatites are enriched in P2O5 (up to 3.6 wt.%), Sr (~2500-5500 ppm), and REE (up to ~2000 ppm) and are, presumably, of liquation genesis. A PREMA-type plume component was a predominant magma source for the complex (εNb () = +6.56... +6.85). According to isotope data (87Sr/86Sr() ~ 0.7032-0.7039; δ18 ~ 7.5-14.9 ; δ13 ~ -2.7...-8.4 ), the fractionation of the melts was accompanied by their crustal contamination. The trace-element composition of the rocks suggests that the complex developed on a continental margin and its development was accompanied by late-collisional rifting and the mixing of moderately depleted (PREMA) and enriched suprasubduction lithospheric mantle (EM I or EM II) with continental crust. It is presumed that the alkaline and carbonatite complexes in the western Central Asian Fold Belt are of primary plume origin and form a LIP within this belt together with other associations produced by Early Paleozoic (510-470 Ma) magmatism.



2.
RECOGNITION OF THE TIME AND LEVEL OF EMPLACEMENT OF THE SILLAI PATTI CARBONATITE COMPLEX, MALAKAND DIVISION, NORTHWESTERN PAKISTAN: CONSTRAINTS FROM FISSION-TRACK DATING

N.U. Khattaka, M. Asif Khana, N. Alib, S.M. Abbasa, and T.K. Tahirkhelia
aNational Centre of Excellence in Geology, University of Peshawar, Peshawar-25120, Khyber Pakhtunkhawa, Pakistan
bPhysics Division, PINSTECH, P.O. Nilore, Islamabad, Pakistan
Keywords: Fission-track dating, age standard approach, apatite, age, Sillai Patti carbonatite, northwestern Pakistan
Pages: 736-744

Abstract >>
The Sillai Patti carbonatite complex represents the second largest carbonatite body of the Peshawar Plain Alkaline Igneous Province of northern Pakistan. It is situated about 20 km west of Malakand, near Sillai Patti Village. Here, the carbonatite occurs along a fault in the form of a sheet striking in the NNE-SSW direction and dipping southward. The carbonatite body is about 12 km long and 2-20 m thick, predominantly intruded along the faulted contact of metasediments and granite gneiss but locally, within the metasediments.
A fission-track age of 29.40 ± 1.47 Ma was obtained for the Sillai Patti carbonatite complex. Close resemblance of the fission-track apatite age of this study with the fission-track as well as other high-temperature radiometric ages from the same and the neighboring carbonatite complexes of the alkaline belt of northern Pakistan suggests emplacement of the Sillai Patti carbonatite complex at higher crustal level and subsequent extremely fast cooling to near ambient temperatures (<60 ?C) required for the complete retention of fission tracks in apatite. The age data also point out that the fission-track age of 29.40 ± 1.47 Ma of this study is the age of intrusion of the carbonatitic magma of the Sillai Patti carbonatite complex to shallow, near-surface level.
Comparison of the uplift-induced denudation rates of the region with the world data clearly reflects the presence of a postcollisonal extensional environment in the region south of the Main Mantle Thrust during Oligocene time. This strongly negates the idea of the earlier workers of emplacement of the carbonatite complexes of the Loe-Shilman and Sillai Patti areas along thrust faults during the Oligocene.



3.
GAS RESERVOIRS IN THE DEAD SEA AREA: EVIDENCE FROM CHEMISTRY OF COMBUSTION METAMORPHIC ROCKS IN NABI MUSA FOSSIL MUD VOLCANO

E.V. Sokola, O.A. Kozmenkoa, S.N. Kokha, and Ye. Vapnikb
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bDepartment of Geological and Environmental Sciences, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105, Israel
Keywords: Paralava, mud volcanism, hydrocarbons, reservoir rocks, Hatrurim Formation, Nubian-type sandstone, Dead Sea
Pages: 975-997

Abstract >>
Nabi Musa located at the northern tip of the Dead Sea at 31?48?N, 35?25?E is one of fifteen complexes of the Hatrurim Formation or the so-called "Mottled Zone" (MZ) which are fossil mud volcanoes. Self-ignition of methane during their eruptions in the Middle-Late Pleistocene caused combustion metamorphism of sediments. Melting foci have been discovered in two craters of Nabi Musa volcano, with numerous veins of paralavas having particular calcic-silicic compositions (Ca2SiO4- and CaSiO3-normative). Their major- and trace-element spectra bear signature of a mixed sedimentary protolith consisting of Cretaceous marine carbonates, marl, and quartz sand. The paralavas inherit high Sr, P, and U enrichments, positive La/La* and Y anomalies, and a negative Ce/Ce* anomaly from calcareous marine sediments, including bituminous and apatite-rich chalks. The presence of quartz arenite in the protolith is responsible for relatively high Ti, Nb, Zr, and Hf, while the marl pelitic component accounts for MREE and LREE depletion. The suggested mixing models predict that the Nabi Musa paralavas result from combustion metamorphism of a sediment mixture with 53-60 wt.% chalk, 5-14 wt.% marl, and 27-44 wt.% quartz arenite. The history of mud volcanism at Nabi Musa began with small eruptions that mobilized gas and water from shallow (within 300 m) Turonian carbonate aquifers, and later explosive activity triggered violent gas blowouts from the older terrigenous reservoir of Aptian-Albian Nubian-type sandstone lying as deep as 1300-1500 m.



4.
THE AGE OF CAMPTONITE DIKES OF THE AGARDAG ALKALI-BASALT COMPLEX ( western Sangilen ): RESULTS OF Ar/Ar AND U/Pb DATING

A.A. Gibshera, V.G. Malkovetsa, A.V. Travinaa, E.A. Belousovab, V.V. Sharygina, and Z. Koncc,d
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bARC Centre of Excellence for Core to Crust Fluid Systems/GEMOC, Dept of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia
cInstituto Andaluz de Ciencias de la Tierra (IACT), Consejo Superior de Investigaciones Cientificas & Universidad de Granada (CSIC & UGR), Avenida de las Palmeras, 418100-Armilla (Granada), Spain
dLithosphere Fluid Research Lab (LRG) Department of Petrology and Geochemistry, Eötvös University, Pázmány Péter sétány, I/C, Budapest, H-117, Hungary
Keywords: Ar/Ar dating, U/Pb dating, camptonite, Sangilen, Tuva
Pages: 998-1013

Abstract >>
A camptonite dike swarm (Agardag alkali-basalt complex) in the western part of the Sangilen Upland abounds in mantle xenoliths. Mineralogical, petrographic, and petrochemical studies showed that the dikes are composed of lamprophyres of two groups, basic and ultrabasic. Ar/Ar dating of amphibole and phlogopite megacrysts yields an intrusion age for the dikes of 443.0 ± 1.3 Ma. 206Pb/238U dating of zircon from a glomeroporphyritic intergrowth in camptonite from one of the dikes yielded a core age of 489.0 ± 5.4 Ma. This corresponds to the time of formation of the Chzhargalanta granite-leucogranite complex (489.4 ± 2.6 Ma). The 206Pb/238U age of the zircon rim is 444.0 ± 7.5 Ma. The ages obtained by Ar/Ar dating of amphibole and biotite megacrysts and by U/Pb dating of the magmatic rim of zircon crystal from the camptonite coincide within the dating error, which indicates that the camptonite dikes formed in the Late Ordovician. These dikes are the oldest-known example of mantle-derived xenoliths in mafic volcanic rocks from an off-craton setting. These are samples of the Upper Ordovician lithospheric mantle.



5.
NEW BIOSTRATIGRAPHIC CONSTRAINTS ON THE LOWER AND LOWER MIDDLE CAMBRIAN OF THE KHARAULAKH MOUNTAINS ( northeastern Siberian Platform, Chekurovka anticline )

I.V. Korovnikov and N.V. Novozhilova
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: Stratigraphy, Lower Cambrian, Middle Cambrian, biostratigraphy, trilobites, small shelly fossils, Chekurovka anticline, Siberian Platform
Pages: 776-786

Abstract >>
The Cambrian section of the western limb of the Chekurovka anticline was studied, with layer-by-layer collection of animal fossils. This permitted us to refine the biostratigraphic division of this section. Four biostratigraphic units (beds) with small shelly fossils were identified: Lapworthella tortuosa , Lapworthella bella , Mobergella radiolata , and Rhombocorniculum cancellatum . They characterize most of the Tommotian and Atdabanian Stages of the Lower Cambrian. The Lower Tyuser Subformation and the Sekten Formation were constrained by small shelly fossils for the first time. Numerous trilobite finds helped to reveal intervals correlating with the Delgadella anabara-Nevadella and Judomia-Uktaspis (Prouktaspis) Regional Zones in the upper Atdabanian.
The upper Sekten Formation (black shales) forms the Kuonamka Formation. Within this interval, the following trilobites were found: Triplagnostus gibbus , Tomagnostus sibiricus , Pseudanomocarina sp., Eodiscus oelandicus , Paradoxides sacheri , and Ptychagnostus aff. atavus . They are widespread in the vast territory of the eastern Siberian Platform, within the Kuonamka Formation.
Also, Korobovia khorbosuonica , Charaulaspis postprimus , and Hebediscus convexa trilobites were observed, which had been found earlier in the Khorbosuonka River section (Olenek uplift). This permits a detailed correlation between these localities.
Similarity was observed between Triangulaspis annio trilobites and young Charaulaspis . This casts doubt upon the fact that the first Triangulaspis annio finds in the northeastern Siberian Platform belonged to the upper Atdabanian.



6.
GEOCHEMISTRY OF BIOMARKERS AND CATAGENESIS OF ORGANIC MATTER OF CRETACEOUS AND CENOZOIC DEPOSITS IN THE INDIGIRKA-ZYRYANKA BASIN ( northeastern Yakutia )

V.A. Kashirtseva, V.V. Gaidukb, O.N. Chalayac, and I.N. Zuevac
aA.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNK Rosneft Joint-Stock Company, ul. Krasnaya 54, Krasnodar, 350000, Russia
cInstitute of Oil and Gas Problems, Siberian Branch of the Russian Academy of Sciences, ul. Oktyabr'skaya 1, Yakutsk, 677891, Russia
Keywords: Indigirka-Zyryanka basin, Cretaceous and Paleogene-Neogene deposits, organic matter, biomarker molecule, oleanane
Pages: 787-797

Abstract >>
Organic matter of Cretaceous and Cenozoic deposits in the Indigirka-Zyryanka basin was studied by bituminological analysis and chromato-mass spectrometry. The regularities of distribution of alkanes and polycyclic aromatic hydrocarbons depending on the catagenesis of fossil organic matter are shown. Sesquiterpanes of the drimane series have been recognized in the Cretaceous deposits, and tetracyclic biomarkers of phyllocladane (kaurane), in the Cenozoic ones. The biomarkers were produced from terpenes of conifers, and the identified set of pentacyclic oleanenes are the products of angiosperms flourishing in the Paleogene and Neogene. As evidenced from geochemical indices, the Cenozoic deposits did not reach the PT -conditions of "the main oil formation zone" and should not be used for the quantitative evaluation of the regional petroleum potential. Nevertheless, the Cenozoic clayey units can be perfect isolating horizons for fluids migrating from more ancient, including Cretaceous, deposits.



7.
STRAIN AND DISPLACEMENT RATES DURING A LARGE EARTHQUAKE IN THE SOUTH BAIKAL REGION

V.Yu. Timofeeva, D.G. Ardyukova, E.V. Boikoa, E.I. Gribanovab, V.M. Semibalamutb, A.V. Timofeeva, A.V. Yaroshevichc
aA.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bSeismological Division of the Geophysical Survey, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Lavrent'eva 13/3, Novosibirsk, 630090, Russia
cIrkutsk Territorial Center for the State Monitoring of the Geologic Environment, ul. Klary Tsetkin 9a, Irkutsk, 664039, Russia
Keywords: Adit strainmeters and tiltmeters, borehole measurements, GPS measurements, strain and displacement rates, earthquakes and coseismic changes, Baikal region
Pages: 798-816

Abstract >>
Crustal kinematic characteristics such as strain and displacement rates are important in the monitoring of present-day processes in zones of seismic and industrial hazard. Strain measurements on different temporal and spatial baselines reveal potentially hazardous zones. Data on coseismic displacements and strain can be used to refine earthquake models, and long-term characteristics are important in searching for earthquake precursors and studying the rheology of the crust and fault zones. Tilt measurements in the adit of the Talaya seismic station (51.68?N, 103.64?E, South Baikal region) began in 1985; strain measurements, in 1990; and GPS measurements, in 2000.
The data reflect time variation in the local strain parameters and permit a comparison with the GPS data on the region and western Central Asia. The data on strain variations obtained in the Ala-Archa underground observatory (42.63?N, 74.50?E, North Tien Shan) are analyzed together with those obtained in the region by GPS methods.
Strain rates on very long baselines were determined using data from permanent IGS stations for Central Asia - the territory expanding from Dzungaria in the south to the Siberian Platform in the north and from the Tien Shan in the west to Lake Baikal in the east. We consider the example of using strain gaging and GPS data to construct a dislocation model and refine the parameters of the Kultuk earthquake (South Baikal region, 27 August 2008, M = 6.3).



8.
HIGH-FREQUENCY INDUCTION DATA AFFECTED BY BIOPOLYMER-BASED DRILLING FLUIDS

I.V. Surodinaa and M.I. Epovb
aInstitute of Computing Mathematics and Mathematical Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Lavrent'eva 6, Novosibirsk, 630090, Russia
bA.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: High-frequency induction logging, biopolymer-based drilling mud, finite-difference modeling
Pages: 817-822

Abstract >>
Biopolymer-based drilling fluids affect data of high-frequency isoparametric induction logging. Highly conductive fluid invaded into drilling-induced flaws produces zones of high resistivity contrasts. Thus, the logs acquire new features that never appear in drilling with argillic mud. These effects have been simulated with regard to high resistivity contrasts for the case of flawed borehole walls, and the modeling results were checked against experimental data.



9.
EFFECTS OF A MUDCAKE ON STONELEY WAVES IN A FLUID-FILLED POROUS FORMATION AROUND A BOREHOLE

A.V. Sineva, E.I. Romenskya,b, and V.N. Dorovskya
aBaker Hugues, Russian Science Center, ul. Kutateladze 4A, Novosibirsk, 630128, Russia
bSobolev Institute of Mathematics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 4, Novosibirsk, 630090, Russia
Keywords: Stoneley waves, permeability, mudcake
Pages: 823-828

Abstract >>
A mudcake formed on the borehole wall between a fluid-filled porous formation and the borehole fluid can affect Stoneley wave propagation used to estimate the formation permeability. The mudcake effect on the permeability dependence of radial oscillations of borehole fluid is investigated in a system with a source generating radial acoustic waves in the borehole and hydrophones (pressure sensors) that record the respective attenuating oscillations of the borehole fluid. The permeability of the porous formation is estimated from theoretical permeability dependence of the attenuation exponent, knowing the time dependence of the exponential attenuation of borehole fluid oscillations.



10.
INVERSION OF HETEROGENEOUS ANISOTROPIC MAGNETOTELLURIC RESPONSES

V.V. Plotkin
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: Electrical anisotropy, synchronous 2D array MT data, lateral heterogeneity, effective conductivity tensor
Pages: 829-836

Abstract >>
Inversion of laterally heterogeneous MT responses collected by a dense synchronous 2D array allows a new approach to estimating electrical anisotropy. The procedure includes solving an overdetermined equation system, assuming distant-dependent anisotropy in a smooth approximation. Inversion is performed using an effective conductivity tensor, which approximates some limited domain of the survey polygon. The algorithm for simulating 2D array MT responses with the effective conductivity tensor approach implies correlation of surface components of the EM field measured simultaneously at all stations within the chosen domain of the survey polygon. The suggested technique of data acquisition and processing ensures reconstruction of the full conductivity tensor from laterally variable components of the EM field.