Geologiya I Geofizika, 2002, V 43, N 2, February.


TECTONICS AND GEOMORPHOLOGY

THE OKHOTSK OCEANIC VOLCANIC PLATEAU N. A. Bogdanov and N. L. Dobretsov 93 The plate of the Sea of Okhotsk is considered as an old oceanic volcanic plateau with tectonic boundaries. Its eastern and western boundaries are formed by right-lateral strike-slip faults; in the north, the plate is bounded by a Middle Cretaceous subduction zone, and the southern boundary is delineated by the ongoing subduction of the Pacific plate beneath Eurasia. On the plate margins (eastern Sakhalin, Taigonos Peninsula, Kuyul Ridge, and Omgon Peninsula in western Kamchatka), relict Middle Jurassic-Lower Cretaceous oceanic crust is exposed in accretionary prisms. The South Okhotsk basin is the largest fragment of the Kula oceanic plate. A volcanic uplift in the center of the Okhotsk plate is identified as the Okhotsk volcanic plateau. In terms of geophysics, the plateau is similar to other volcanic plateaus, such as Ontong-Jawa, Shatsky, Hess, etc. It is hypothesized that the Okhotsk volcanic plateau formed north of the mid-ocean ridge, within the Kula plate, in response to the late Jurassic-early Cretaceous activity of a hot mantle plume in the region of the triple junction of the Kula, Pacific, and Faralon plates. As a result of the northward motion of the Kula plate with the Okhotsk plateau, the latter blocked subduction beneath the Okhotsk-Chukchi volcanoplutonic belt in the late Turonian. Subduction zones blocked by oceanic volcanic structures are of broad occurrence near accretionary fold-nappe belts. Oceanic volcanic plateau, subduction, collision, accretionary prism, ophiolites, Sea of Okhotsk
FORMATION OF THE LATE PALEOZOIC STRUCTURE OF THE TELETSKOE REGION: KINEMATICS AND DYNAMICS (Gorny Altai-West Sayan junction) L. V. Smirnova, K. Theunissen, and M. M. Buslov 107 The Late Paleozoic structure and evolution of the junction between Gorny Altai and West Sayan is considered on the basis of geochronology and structural analysis by morphological, stereogeometric, and microstructural methods. The distinguished evolution stages of the region (Early-Middle Devonian, Late Devonian-Early Carboniferous, and Permian) fit the general geodynamic setting of the Altai-Sayan folded area. The Early-Middle Devonian stage was marked by intrusion of the Altyntauss granitoids into greenschist rocks. During the Late Devonian-Early Carboniferous stage, the Teletskoe shear zone was initiated along the eastern margin of the Altyntauss pluton. The formation of the shear zone was accompanied by strike-slip and thrust faulting under NW-SE compression and corresponds to the stage of collision between Siberia and the Altai-Mongolian terrane. According to new data, the northern part of the shear zone may have been produced by thrusting that acted simultaneously with left-lateral strike-slip motions on the major fault. The amount of horizontal displacement is estimated at about 80 km. The Permian stage corresponds to the Kazakhstan-Siberia collision and was associated with the formation of the North Sayan strike-slip fault under WE compression, with the right-lateral slip of about 30 km. The North Sayan fault truncates and deforms the Late Devonian-Early Carboniferous structure. Structure, kinematics, strike-slip fault, Paleozoic basement
RADON ANOMALIES AS EVIDENCE FOR ACTIVITY OF THE WEST SAYAN FAULT IN NORTHERN LAKE TELETSKOE (Gorny Altai) B. Dehandshutter, V. A. Bobrov, R. Hus, N. E. Astakhov, N. V. Androsova, and Yu. P. Popov 120 Lake Teletskoe, a major neotectonic unit of Gorny Altai, is a complexly structured graben formed during reactivation of Late Paleozoic fault zones. The formation of the graben in the northern part of the lake has been controlled by the West Sayan fault. The ongoing activity of the fault is evidenced by radon and mercury anomalies whose behavior was investigated by measurements along profiles perpendicular to active fault segments by various methods. Radon flux observed in activated charcoal showed anomalies over faults. Radon emanation in the soil-gas system was measured by scintillation and electric detectors that enable detection of anomalies in soil gas over fault zones. The concentration of radon measured in springs marked faults infiltrated with radon water. Enhanced concentrations of mercury measured in soil and water along the fault zone revealed an open fissure system channeling gas fluids. Therefore, the West Sayan fault zone is an active structure that provides vertical migration of radon and mercury. Radon, fault, neotectonics, vertical migration, gas geochemistry, Lake Teletskoe
PALEOHYDROLOGY OF LAKE BAIKAL IN RELATION TO NEOTECTONICS V. D. Mats, S. Fujii, K. Mashiko, L. Z. Granina, E. Yu. Osipov, I. M. Efimova, and A. V. Klimanskii 134 New data prove that the rise of the Baikal level in the past (to 120-150 m) may have really occurred and was caused by tectonic uplift of the western side of the Baikal basin. As the lake level rose, medium and high terraces were forming and sands deposited in the Selenga delta and elsewhere; the discharge through the Lena along the paleo-Manzurka valley (2.0-0.5 Ma ago) was blocked, and a new outlet appeared through the Il'cha-Irkut valley into the Yenisei system (0.5-0.6 Ma ago). That outlet was broken about 60 ka ago by the collapse of the Listvyanka block, which at the same time produced the present-day discharge channel through the Angara. Calculations show that the lake level may hardly have dropped for a geologically long time, but short episodes of low stand were possible. The terraces on the lake sides result from the joint effect of tectonic and hydrological factors. Analysis of the past evolution of the river network in the Western Baikal region allowed prediction of its possible changes in the future. Water level fluctuations, terraces, evolution of drainage network, Lake Baikal
PALEONTOLOGY

A MESOZOIC OCEAN IN ARCTIC: PALEONTOLOGICAL EVIDENCE V. A. Zakharov, B. N. Shurygin, N. I. Kurushin, S. V. Meledina, and B. L. Nikitenko 147 The fauna of Mesozoic epicontinental seas that existed on the territory of the present-day Arctic margin of Eurasia, North America, and islands in the Arctic Ocean is dominated by stenohaline mollusks (ammonoids, coleoids, bivalves, gastropods, brachiopods, foraminifers, ostracods, radiolarians, etc.). The marine biota consists of cosmopolitan taxa of the boreal Pacific and boreal Atlantic origin, Tethyan immigrants, and endemics, including hundreds of endemic species, tens of endemic genera, and six endemic families. Numerous lines of invertebrates in the Arctic basin evolved sustainably for tens of millions of years. The high taxonomic diversity of the specific marine biota and the ways of its panboreal migration could have been maintained by an oceanic basin that existed on the territory of the present-day Arctic throughout the Mesozoic, as a great volume of oceanic water was necessary to provide stable salinity and temperature in the surrounding epicontinental basins through 180 Ma. Long and sustainable development of the specific Mesozoic marine biota was provided by the South Anyui ocean in Triassic and Jurassic time and by the Amerasian ocean in the Cretaceous. This evidence substantiates the hypothesis of the presence of oceans in the Arctic territory through the Mesozoic which was suggested proceeding from geodynamic reconstructions. Mesozoic, paleoocean, paleontology, geodynamics, paleobiogeography, Arctic
PETROLOGY, GEOCHEMISTRY, AND MINERALOGY

THE MECHANISM OF TRACE-ELEMENT INTAKE DURING CRYSTAL GROWTH V. L. Tauson, I. Yu. Parkhomenko, V. I. Men'shikov, and K. V. Nepomnyashchikh 174 The mode of occurrence of cadmium in stoichiometric pyrrhotite synthesized hydrothermally at 450 C and 1 kbar was studied by combined atomic absorption spectroscopy and thermal analysis. The results, along with the available data on relatively highly fugitive elements (Cd, Pb) in solid phases, show that sorption may play a key role in the intake of incompatible elements during crystal growth under the PT-conditions of endogenic mineral formation. Incompatible elements in a growing crystal form an adsorbed surface compound or a complex if their concentration is relatively low or a surface nonautonomous phase if their concentration approaches the saturation limit. Of this concentration, only a small portion may be in the structural form, and special techniques are thus required to separate it if the occurrence limit of the elements is estimated by routine methods. Incompatible elements, trace elements, mode of occurrence, sorption, endocrypty, cadmium, pyrrhotite
GEOLOGY OF OIL AND GAS

AN OLD OIL AND GAS ACCUMULATION ZONE IN THE SOUTHERN SIBERIAN PLATFORM (Katanga uplift) A. V. Khomenko, E. N. Kuznetsova, and A. O. Gordeeva 180 The paper presents evidence that a large synsedimentary uplift existed in the southern Siberian Platform in the Early Paleozoic, which has been a zone of oil and gas accumulation since the late Early Cambrian. A number of carbonate reservoirs within the uplift yielded flows of petroliferous fluids and possibly contain the greatest portion of the oil and gas resources of the region. Cambrian, synsedimentary structure, hydrocarbons, Siberian Platform
GEOPHYSICS

RECALCULATION OF STANDING WAVES IN DETAILED SEISMOLOGICAL ENGINEERING STUDIES A. F. Emanov, V. S. Seleznev, A. A. Bakh, S. A. Gritsenko, I. A. Danilov, A. P. Kuz'menko, V. S. Saburov, and G. I. Tat'kov 184 A new approach is suggested that enables detailed seismological engineering investigation of buildings, bridges, dams, etc. by the method of standing waves using small-channel instruments. Recalculation of standing waves from one point to another, which is possible to a predetermined accuracy, allows simultaneous recording of standing waves on networks of points of any density from microseismic records obtained at these points at different times. Specific features of observation systems and standing waves recalculation algorithms are considered for various types of structures. Experimental data show that the new method has high potentialities for detection and detailed investigation of standing waves in engineering structures. Investigation of the geometry of standing waves and spatial distribution of phases provides information on the physical state of the structures. The new method is highly effective and cheap. Engineering seismology, standing waves, Wiener filter