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Russian Geology and Geophysics

2009 year, number 8

Tectonic map of the Vendian-Lower Paleozoic structural stage of the Lena-Tunguska petroleum province, Siberian Platform

A.E. Kontorovich a , S.Yu. Belyaeva, A.A. Kontorovich b , V.S. Starosel'tsev c , M.M. Mandel'baum d , A.V. Migurskii c , S.A. Moiseev a , A.F. Safronov e , V.S. Sitnikov f , Yu.A. Filiptsov g , A.V. Khomenko a , Yu.G. Eremin a , O.V. Bykova a
a Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Krasnoyarskgeofizika, 24v ul. Partizana Zheleznyaka, Krasnoyarsk, 660022, Russia
c Siberian Research Institute of Geology, Geophysics and Mineral Resources, 67 Krasnyi prosp., Novosibirsk, 630091, Russia
d Irkutskgeofizika, 8 ul. Gor'kogo, Irkutsk, 664025, Russia
e Institute of Oil and Gas Problems, Siberian Branch of the RAS, 1 ul. Oktyabrskaya, Yakutsk, 677891, Russia
f State Committee of the Sakha Republic (Yakutia) for Geology and Subsoil Resource Management, 13 ul. Kirova, Yakutsk, 677892, Russia
g Mineral Resources Management of Krasnoyarsk Territory, 62 ul. Marksa, Krasnoyarsk, 660049, Russia
Keywords: sedimentary cover; petroleum complex; structure map; classification; tectonic map; Siberian Platform
Pages: 649-659

Abstract >>
A new version of the tectonic map for the Vendian-Lower Paleozoic structural stage of the Lena-Tunguska petroleum province is presented. The map is based on the electronic structure map at a scale of 1:1,000,000, which was the first to be compiled for the uppermost Vendian within the study area. However, no tectonic zonation was made for the deep-buried Meso-Cenozoic Yenisei-Khatanga and Vilyui depressions. The principles and methodology of mapping are given. The study presents spatial, morphological, and quantitative characteristics of the major and large structures.

Formation of the Olyutorsky-Kamchatka foldbelt: a kinematic model

M.N. Shapiro a , A.V. Solov'ev b
a Institute of the Physics of the Earth, Russian Academy of Sciences, 10 ul. Bol'shaya Gruzinskaya, Moscow, 123995, Russia
b Geological Institute, Russian Academy of Sciences, 7 Pyzhevskii per., Moscow, 119017, Russia
Keywords: Late Mesozoic-Cenozoic; plate kinematics; northwestern Pacific; Olyutorsky-Kamchatka foldbelt
Pages: 660-673

Abstract >>
The Olyutorsky-Kamchatka foldbelt formed as a result of two successive collisions of the Achaivayam-Valaginsky and Kronotsky-Commander island arcs with the Eurasian margin where the two terranes docked after a long NW transport. We model their motion history from the Middle Campanian to Present and illustrate the respective plate margin evolution with ten reconstructions. In this modeling the arcs are assumed to travel on the periphery of the large plates of Eurasia, North America, Pacific, and Kula, for which the velocities and directions of motion are known from published data. The model predicts that the Achaivayam-Valaginsky arc was the leading edge of the Kula plate from the Middle Campanian to the Middle Paleocene and then moved slowly with the Pacific plate as long as the Middle Eocene when it accreted to Eurasia. The Kronotsky arc initiated in the Middle Campanian on the margin of North America and was its part till the latest Paleocene when the terrane changed polarity to move northwestward with the Pacific plate and eventually to collide with Eurasia in the Late Miocene. The predicted paleolatitudes of the Achaivayam-Valaginsky and Kronotsky-Commander island arcs for the latest Cretaceous and Paleogene are consistent with nine (out of eleven) reliable paleomagnetic determinations for samples from the two arcs. Additional changes imposed on the initial model parameters (kinematics of the large plates, relative position of the Kula-Pacific Ridge and the Emperor seamount chain, or time of active volcanism within the arcs) worsen the fit of the final reconstructions to available geological and paleomagnetic data. Therefore, the suggested model appears to be the most consistent one at this stage of knowledge.

Radon activity of faults(western Baikal and southern Angara areas)

K.Zh. Seminsky, A.A. Bobrov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: radon; fault; tectonic activity; Baikal rift; Siberian craton
Pages: 674-684

Abstract >>
We report results of transect radon surveys on twenty six large and small faults of different geometries in the western Baikal and southern Angara (southern Siberian craton) areas. The studied faults show up in the radon field as broad zones of high radon activity concentration, with their widths 1.4 times the widths of faulting-related deformation zones. Other things being equal, radon emanation depends on the size and slip geometry of faults and on their activity in the Cenozoic. Relative radon activity is higher in rift faults than in cratonic ones, in normal relative to strike-slip faults, and in larger and more active faults, the latter factor being the basic geodynamic control of radon emanation.

The Asachinskoe epithermal Au-Ag deposit in southern Kamchatka: physicochemical conditions of formation

A.A. Borovikov, A.S. Lapukhov, A.S. Borisenko, Yu.V. Seryotkin
Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: fluid inclusions; Au-Ag deposits; ore formation
Pages: 685-694

Abstract >>
The Asachinskoe epithermal Au-Ag deposit (southern Kamchatka) is referred to as low-sulfidation in quartz-adularia-sericite in Corbett's classification. Research into fluid inclusions of its minerals gave an insight into the PT -conditions of formation and gas composition of ore-forming fluids as well as the vertical variations in these parameters to a depth of more than 200 m within a 2 km long horizontal site of the deposit ore zone. It is shown that mineral assemblages formed at 320 to <100 °C. Ore-forming hydrothermal solutions were poor in salts (3-9.2 wt.% NaCl equiv.), with NaCl being the main component. Mineral assemblages with high contents of Au crystallized at 250-175 °C. Ore-free quartz-carbonate veins formed at 80-120 °C. High-temperature (300-320 °C) veins also lack ores. Rich gold ores were deposited in the environments where ore-bearing fluids boiled, mixing with meteoric waters.

Fayalite-sekaninaite paralava from the Ravat coal fire (central Tajikistan)

V.V. Sharygin a , E.V. Sokol a , D.I. Belakovskii b
a Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Fersman Mineralogical Museum, Russian Academy of Sciences, 18 Leninskii prosp., str. 2, Moscow, 119071, Russia
Keywords: fayalite; sekaninaite; clinoferrosilite; hercynite; tridymite; paralava; coal; Ravat coal fire; Fan-Yagnob coal deposit
Pages: 695-713

Abstract >>
We studied ferrous paralava, a high-temperature rock, produced by complete fusion of the sedimentary protolith in the Ravat natural coal fire which has been on for over two thousand years. The paralava was sampled from the Fan-Yagnob coal deposit at the Kukhi-Malik site in the vicinity of former Ravat Village in central Tajikistan. This rock contains fayalite, sekaninaite, hercynite, Ti-magnetite, tridymite, and siliceous glass. Low-Ca pyroxene (clinoferrosilite), globules of sulfides (mainly pyrrhotite) and Fe-Ti oxides, secondary greenalite (after fayalite) and hematite are minor. Paralava includes xenoliths of partially molten clinkers (up to 20 vol.%) composed of mullite, cordierite, tridymite, and relict detrital quartz. We found relatively high Fe contents (100 · Fe/(Fe+Mg) > 60) in mafic minerals, high K2O enrichment (up to 1.4 wt.%) in sekaninaite, and an unusually low CaO content (0.5 wt.%) in the rock. The Ravat paralava appears to be derived from a mixture of pelitic rocks (50-70%) and iron-rich rocks (30-50%), but without participation of calcareous material, which explains the low CaO and the absence of plagioclase and Ca-bearing pyroxene. The primary melt was as hot as >1210 °C, and the coal-fired fayalite-sekaninaite paralava crystallized at 1200-1100 °C, at a relatively low oxygen fugacity (near the QFM buffer), outside the zone of active aeration. Large-scale crystallization of ferrospinels and fayalite led to increasing Al2O3 and SiO2 in the melt whence sekaninaite and tridymite crystallized as later phases. The residual melt progressively acquired a more silicic-aluminous composition, rich in K2O, CaO, and P2O5, and became quenched to glass at >1080-1090 °C, when temperature dropped abruptly, possibly, by roof collapse or opening of large cracks, as it usually happens in underground coal fires.

Types of Holocene deposits and regional pattern of sedimentation in Lake Baikal

E.G. Vologina a , M. Sturm b
a Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
b Swiss Federal Institute of Aquatic Science and Technology EAWAG-ETH, CH-8600 Dubendorf, Switzerland
Keywords: bottom sediments; sedimentation; pelagic mud; turbidites; Lake Baikal
Pages: 714-719

Abstract >>
Results of research into recent sediments and their distribution in Lake Baikal are presented. Five areas with different mechanisms of sedimentation have been recognized: (1) deep-water plains with pelagic mud and turbidites; (2) littoral zones without turbidites; (3) underwater ridges (rises) with hemipelagic mud accumulated under calm sedimentation conditions; (4) delta (fan) areas near the mouths of large rivers, where sediments consist mainly of terrigenous material; and (5) shallow Maloe More with poorly sorted terrigenous material and abundant sand. The rate of sedimentation differs considerably in different Baikal areas. The highest rates appear near the mouths of large rivers, lower ones occur in the deep lake basins, and the minimum rates are developed on underwater ridges. A map of the distribution of Holocene sediments in Baikal has been compiled for the first time. The obtained results show that the bottom morphology significantly determines the type of sediments in the lake.

Conductivity of layered reservoirs in induction data processing: continuous-function approximation

V.N. Glinskikh, M.I. Epov
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: layered formation; numerical modeling; high-frequency induction sounding; electrical conductivity; continuous function
Pages: 720-725

Abstract >>
We suggest to approximate the depth-dependent conductivity of layered formations by continuous functions and use this approach to design an algorithm for 2D inversion of induction logging data. The logs represent formations consisting of alternating thin clay and sand layers of varying thickness, in which the sand layers can involve a developed invaded zone of a complex structure. Comparison of synthetic logs in models with piecewise constant and continuous approximations of conductivity shows that the continuous-function approximation is accurate within 5%, and the accuracy improves as the average conductivity of the layered formation is taken into account.

Strain amplitude-dependent attenuation of P and S waves in dry and water-saturated sandstone under confining pressure

E.I. Mashinskii
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: anelasticity; nonlinear stress-strain relation; hysteresis; anelastic seismic parameters; relaxation spectra; strain amplitude dependence of wave velocity and attenuation
Pages: 726-731

Abstract >>
The dependence of P - and S -wave attenuation on strain amplitude and frequency has been studied experimentally in dry and water-saturated sandstone samples under a confining pressure of 20 MPa. Attenuation of P and S reflections was measured at a frequency of 1 MHz in a strain range of ε ~ (0.3—2.0) ·10–6. The measured P -wave attenuation ( QP–1) in dry sandstone and S -wave attenuation ( QS–1) in dry and saturated samples turned out to be inversely proportional to strain amplitude while QP–1 in saturated sandstone showed no strain dependence. The frequency-dependent attenuation spectra in dry and saturated sandstone differed considerably in S waves but were generally similar for P reflections. Strain amplitude variations were found out to influence the frequency dependence of attenuation and to shift the relaxation spectra of S waves toward high frequencies relative to those of P waves. As strain increased, the S -wave attenuation peak in saturated sandstone became notably (to 40%) narrower. The unusual strain amplitude-dependent behavior of attenuation may be due to joint action of viscoelastic and microplastic mechanisms. The reported results may be useful for improving geological interpretation of acoustic and seismic data.