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Russian Geology and Geophysics

2017 year, number 11

1.
MIDDLE-LATE PALEOZOIC GEODYNAMIC COMPLEXES AND STRUCTURE OF GORNY ALTAI AND THEIR RECORD IN GRAVITY DATA

N.L. Dobretsov1,2, M.M. Buslov3,2, E.S. Rubanova3,2, A.N. Vasilevsky1,2, A.V. Kulikova3,2, E.A. Bataleva4
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
4Research Station of the Russian Academy of Sciences in Bishkek, Bishkek, 720049, Kyrgyzstan
Keywords: Tectonics, geodynamics, shear zone, detrital zircons, granites, volcanoplutonic complexes, zoned metamorphic complexes, gravity field, Gorny Altai

Abstract >>
Middle-Late Paleozoic geodynamics and structure of Gorny Altai are studied with reference to gravity data. The northern and central parts of the area belong to the Gorny Altai terrane consisting of Late Precambrian-Paleozoic rocks originated in different tectonic settings on the Siberian continental margin, including Devonian active-margin volcanoplutonic complexes. In the south and east, the Gorny Altai terrane borders the Altai-Mongolia terrane along the Charysh-Terekta-Ulagan shear zone. The Altai-Mongolia terrane is composed of Early Paleozoic turbidites of the Kazakhstan-Baikal continent, Middle Paleozoic collisional garnet-disthene-andalusite schists, and Late Paleozoic zoned andalusite-cordierite schists, with granitic plutons on their periphery. The pattern of these complexes is similar to that of Cenozoic volcanoplutonic and metamorphic domes in the Kamchatka and Chukchi Peninsulas. The Devonian volcanoplutonic complexes from the Gorny Altai terrane and the Middle-Late Paleozoic metamorphic complexes from the Altai-Mongolia terrane are well evident in the gravity field. In general, gravity anomalies in the two terranes strike in different directions: NW in the Gorny Altai terrane and W-E in the Altai-Mongolia terrane, which highlights the structural heterogeneity of the Gorny Altai region. New dates have been obtained for magmatic detrital zircons from Paleozoic sedimentary rocks of the Anui-Chuya basin in the Gorny Altai terrane. The inferred source areas of zircon hosts are igneous rocks of the Precambrian craton basement and the Vendian-Early Ordovician Kuznetsk-Altai island arc. Early Neoproterozoic (1.00-0.75 Ma) detrital zircons are abundant in the Early Paleozoic turbidites of the Altai-Mongolia terrane but are absent from samples of the Gorny Altai terrane. Populations of detrital zircons in the the Gorny Altai terrane contain Devonian and Early Neoproterozoic specimens. The reported data prove that the Kazakhstan-Baikal and Siberian continents amalgamated in the Middle-Late Paleozoic. The resulting Gorny Altai tectonic framework of that time is recorded in the gravity field and in the provenance of detrital zircons.



2.
MANTLE HETEROGENEITY AT THE BOUVET TRIPLE JUNCTION BASED ON THE COMPOSITION OF OLIVINE PHENOCRYSTS

N.A. Migdisova1, A.V. Sobolev1,2, N.M. Sushchevskaya1, E.P. Dubinin3, D.V. Kuzmin4
1Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia
2Institut des Sciences de la Terre (ISTerre) Université J. Fourier-CNRS Maison des Géosciences, Grenoble Alpes CS 40700 38058 GRENOBLE Cedex 9
3Moscow State University, Leninskie Gory GSP-1, Moscow, 119991, Russia
4V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Mid-ocean ridges, tholeiites, pyroxenitic component, peridotite, primary melts, Bouvet triple junction

Abstract >>
Tholeiitic melts from the Bouvet triple junction (BTJ) of rift zones in the South Atlantic are moderately enriched rocks with specific lithophile-element patterns. The high (Gd/Yb) n values (up to 2.5) in some tholeiite compositions suggest the presence of garnet in the mantle source of primary BTJ melts. The high Ni and low Mn contents of the most magnesian olivines determined by high-precision probe microanalysis suggest the presence of pyroxenite, along with typical peridotite, in the melting source. The unusually wide within-sample variation in the proportions of pyroxenitic component in the source region ( X Px Mn/Fe = 0-90%) indicates different degrees of mantle heterogeneity beneath the spreading zone. Based on geochemical data, this component is a silica-oversaturated eclogite, reacting with peridotite to form olivine-free pyroxenite in the melting source. This component is probably represented either by subducted and recycled oceanic crust or by fragments of the ancient continental lithosphere buried into the mantle after the Gondwana breakup. The observed global and local mantle heterogeneities might have been developed during the complex geodynamic evolution of the Southern Ocean, whose opening was affected by the activity of the Mesozoic Karoo-Maud-Ferrar plume and multiple jumps of the spreading axes, which led to the involvement of fragments of the early oceanic lithosphere in the melting process.



3.
Nd-Sr-Os SYSTEMS OF ECLOGITES IN THE LITHOSPHERIC MANTLE OF THE KASAI CRATON (Angola)

L.P. Nikitina1,2, E.S. Bogomolov1,3,4, R.Sh. Krymsky5, B.V. Belyatsky5, N.M. Korolev1, V.N. Zinchenko6
1Institute of Precambrian Geology and Geochronology, nab. Makarova 2, St. Petersburg, 199034, Russia
2St. Petersburg State University, Institute of Earth Sciences, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russia
3A.P. Karpinsky Russian Geological Research Institute
4Srednii prosp. 74, St. Petersburg, 199106, Russia
5A.P. Karpinsky Russian Geological Research Institute, Srednii prosp. 74, St. Petersburg, 199106, Russia
6Department of Geology, Catoca Geological-Mining Community, Luanda, Republic of Angola
Keywords: Upper mantle, eclogites, Nd-Sr-Os systems, model isotopic age, genesis

Abstract >>
We studied the Sm-Nd, Rb-Sr, and Re-Os isotope compositions of mantle xenoliths (eclogites and peridotites) from diamondiferous kimberlites of the Catoca cluster of the Kasai Craton. In the eclogites, the primary strontium isotope composition 87Sr/86Sr varies from 0.7056 to 0.7071, and the neodymium isotope composition εNd, from 1.8 to 2.6. The 187Re/188Os and 187Os/188Os ratios range from 135 to 80 and from 1.3110 to 1.9709, respectively, which indicates a significant portion of radiogenic 187Os: γOs = 129-147. These isotope values exceed the values assumed for model reservoirs (primitive upper mantle (PUM) and bulk silicate Earth (BSE)) and those of chondrites. The isotope composition of the studied systems indicates the formation of eclogites from a rhenium-enriched source, namely, the subducted oceanic crust transformed as a result of metasomatism and/or melting under upper-mantle conditions.



4.
NUMERICAL MODELING OF THE MECHANISMS OF MAGMA MINGLING AND MIXING: A CASE STUDY OF THE FORMATION OF COMPLEX INTRUSIONS

A.N. Semenov1,2, O.P. Polyansky1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2S.A. Khristianovich Institute of Theoretical and Applied Mechanics, Russian Academy of Sciences, ul. Institutskaya 4/1, Novosibirsk, 630090, Russia
Keywords: Magma mingling, mixing, convection, melt, viscosity, crystallization, numerical modeling, intrusion, dike

Abstract >>
This paper describes a thermomechanical mathematical model of magma mingling and mixing during the formation of complex intrusions and presents the first results of numerical modeling. The model considers one-pulse intrusion of mafic or intermediate melts into a granitoid magma chamber. The model is based on literature data on the composition and structure of two polychronous intrusions: the Burgas quartz syenite massif and the Magadan granitoid batholith. The modeling shows that the main parameter controlling the convection regime is the density difference. The density and viscosity contrasts of interacting magmas during mingling and mixing are estimated. Depending on the density difference, one of the possible processes dominates: In the case of a small difference (less than 30-40 kg/m3), magma mixing and hybridization in a small contact zone takes place; in the case of a large difference (100 kg/m3 or more), magma mingling predominates. The viscosity contrast, in turn, determines whether interpenetration of melts or fragmentation of melts in the form of drops, spheres, etc. occurs. There is a limiting viscosity of salic magma (108 Pas) at which the flows freeze in the chamber and further cooling occurs with a slowly moving fluid. The time of formation of mingling structures is estimated to be several days to several hundred years, depending on the initial melt viscosity.



5.
CONDITIONS OF METAMORPHISM OF GARNET-BEARING ALUMINOUS GNEISSES IN THE OREKHOV-PAVLOGRAD ZONE OF THE UKRAINIAN SHIELD

Sh.K. Baltybaev1, A.V. Yurchenko1, S.B. Lobach-Zhuchenko1, V.V. Balagansky2, O.L. Galankina1, M.V. Morozov3, E.S. Bogomolov1
1Institute of Precambrian Geology and Geochronology, nab. Makarova 2, St. Petersburg, 199034, Russia
2Geological Institute of the Kola Science Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, Murmansk Region, 184209, Russia
3Tellur North-East LLC, ul. Soyuza Pechatnikov 8, St. Petersburg, 199000, Russia
Keywords: Metamorphism, garnet, aluminous gneisses, regularly oriented inclusions, Paleoproterozoic, thermobarometry, Sm-Nd system

Abstract >>
Garnet-bearing aluminous gneisses in the Vasilkovka area of the Orekhov-Pavlograd zone of the Ukrainian Shield were studied using the THERIAK-DOMINO, THERMOCALC, and WINTWQ software and mineral geothermobarometry methods. The stability fields of parageneses formed at the initial, peak, and post-peak metamorphic stages have been estimated: T = 500-650 ºC and P > 7 kbar, T = 800-850 ºC and P ≈ 8 kbar, and T = 600-670 ºC and P = 4.0-5.5 kbar, respectively. A «clockwise PT path has been established. Based on the aluminous gneiss, the age of metamorphism is determined as Paleoproterozoic (2014 11 Ma). Unique regularly oriented acicular goethite microinclusions were described in garnet. In contrast to other known oriented Ti-bearing mineral inclusions in garnet, these goethite inclusions suggest not only extremely high P and T values (necessary for the formation of oriented Ti-bearing inclusions) but also a high oxygen fugacity. The obtained data broaden the concepts of the ways and conditions of formation of regularly oriented mineral phases in garnet.



6.
GEOCHEMISTRY OF THE BARITE DEPOSITS NEAR ADANA-FEKE AREA (Eastern Taurides)

Afitap Tas Ozdogan1, Yusuf Uras2, Fevzi Oner3
1MTA Dogu Akdeniz Bolge Mudurlugu, Universiteler, Mahallesi Dumlupinar Bulvari No:139 06800, Ankara, Turkey
2Kahramanmaras Sutcu Imam University, Faculty of Engineering and Architecture, Department of Geological Engineering, 46040, Kahramanmaras, Turkey
3Mersin University, Faculty of Engineering and Architecture, Department of Geological Engineering, Mersin, Turkey
Keywords: Feke (Adana), barite, rare earth elements, fluid inclusions, isotope

Abstract >>
The barite deposits that emerge as veins and lodes within or along the contact zones of recrystallized limestone and dolomite units of Cambrian Degirmentas Formation are of epigenetic character. Depositional styles, paragenesis, host rock alteration styles, and high SrO contents of the barites suggest a hydrothermal origin for their formation. However, considering their rare earth element compositions, barite samples surround the field for seawaters when plotted on Ce N / Yb N -Yb N and Ce N /Sm N -Ce N /Yb N diagrams. Fluid inclusion data obtained from the barites indicated a formation from a fluid with low salinity (0.9-1.6 wt.% NaCl eq.) at homogenization temperatures between 78 and 190C. Sulfur isotopic compositions of barites vary between +32.2 and +36.3, and their 87Sr/86Sr values range between 0.709885 and 0.749652. Depositional styles, parageneses, trace element compositions, fluid inclusion data as well as δ34S and 87Sr/86Sr isotopic data indicate a model in which hydrothermal fluids were possibly derived from a buried intrusion mixed with meteoric and marine waters, further interacting with the Precambrian - Phanerozoic metaclastic and Cambrian carbonate rocks to form barite deposits.



7.
METAL-BEARING FLUIDS AND THE AGE OF THE PANIMBA GOLD DEPOSIT (Yenisei Ridge, Russia)

N.A. Gibsher1, M.A. Ryabukha1, A.A. Tomilenko1, A.M. Sazonov2, N.O. Khomenko1, T.A. Bulbak1, N.A. Nekrasova2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Institute of Mining, Geology, and Geotechnology of Siberian Federal University, pr. Imeni Gazety Krasnoyarskii Rabochii 95, Krasnoyarsk, 660025, Russia
Keywords: Quartz, gold, fluid inclusions, hydrocarbons, Ar-Ar age

Abstract >>
The Panimba gold deposit lies in the rocks of the epidote-amphibolite metamorphism facies and is confined to the exocontact zone of the Chirimba granitoid massif. Fluid inclusions in quartz and sulfides of two sites of the deposit, Mikhailovka and Zolotoi Brook, were studied by thermobarogeochemistry, gas chromatography, and chromatography-mass spectrometry. We have established that gold-quartz veins of the deposit were formed by metal-bearing Mg-Na-Cl-containing water-carbon dioxide-hydrocarbon fluids with salinity of 8-23 wt.% NaCl eq. at temperatures of 180 to 410 ºC and pressures of 0.2 to 3.3 kbar. Hydrocarbons and nitrogen- and sulfur-containing compounds of the fluids can transport gold and might be positive indicators of the gold presence in quartz veins. Fluids with salinity of >30-40 wt.% and sulfur isotope values (δ34S) of 0.9 to 6.7 of sulfides are the result of the action of postmagmatic solutions of the nearby Chirimba granitoid massif. The age of hydrothermal gold-sulfide mineralization of the Panimba deposit is within 817.2 5.3-744 17 Ma and falls in the time interval of crystallization of the Chirimba intrusion, 868.9 6.5 to 721.4 1.6 Ma, but it is considerably younger than the age of the regional metamorphism (996 32-889 26 Ma).



8.
COMPOSITION OF ALKYL ARENES OF PHANEROZOIC OILS

G.S. Pevneva1, A.K. Golovko1,2
1Institute of Petroleum Chemistry, Siberian Branch of the Russian Academy of Sciences, Akademicheskii pr. 4, Tomsk, 634055, Russia
2Tomsk Department of the A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Akademicheskii pr. 4, Tomsk, 634055, Russia
Keywords: Oil, alkyl benzenes, alkyl naphthalenes, alkyl phenanthrenes

Abstract >>
We summarize the results of our long-term research into the composition of alkyl derivatives of mono-, bi-, and tricyclic aromatic hydrocarbons of 113 crude oils from the Cenozoic (Sakhalin, Pannonian Basin (Serbia), China, and Vietnam), Cretaceous (West Siberia, Mongolia, China, and Saxony), Jurassic (West Siberia and Saxony), and Paleozoic (West Siberia, East Siberia, and Timan-Pechera and Volga-Ural petroliferous provinces) deposits localized at depths from 200 to 4500 m. To identify compositional similarities and differences of crude oils from deposits of different ages, we processed the obtained data on the individual composition of alkanes, alkyl benzenes, alkyl naphthalenes, and alkyl phenanthrenes by principal-component analysis. The analysis has revealed the regularities of changes in the content and composition of alkyl aromatic hydrocarbons in crude oils depending on the age of the enclosing deposits.



9.
AUTHIGENIC CARBONATE SEDIMENTATION IN ERAVNOE GROUP LAKES (western Transbaikalia): RESPONSE TO HOLOCENE CLIMATE CHANGE

E.P. Solotchina1, E.V. Sklyarov2,3, P.A. Solotchin1, L.V. Zamana4, I.V. Danilenko1, O.A. Sklyarova5, P.G. Tatkov6
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
3Far East Federal University, ul. Sukhanova 8, Vladivostok, 690950, Russia
4Institute of Natural Resourses, Environment, and Cryology, Siberian Branch of the Russian Academy of Sciences, ul. Butina 26, Chita, 672090, Russia
5Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, 664033, Irkutsk, Russia
6Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakhyanovoi 6a, Ulan-Ude, 670047, Russia
Keywords: Bottom sediments, carbonates, XRD analysis, infrared spectroscopy, 18O and 13C isotopes, Late Holocene, paleoclimate, Lake Dolgoe, Eravnoe basin, East Siberia

Abstract >>
Sediments of intracontinental closed lakes are unique natural archives that store climate history records. We study Late Holocene carbonate-bearing sediments of Lake Dolgoe, a small saline lake in the Eravnoe basin on the Vitim Plateau (western Transbaikalia). Sediment samples have been analyzed by several methods: powder X-ray diffractometry, Infrared spectroscopy, stable isotope (18O and 13C) determination, laser diffraction particle size analysis, XRF elemental analysis, etc. The mineral phases of bottom sediments include clastic and carbonate components and hydromagnesite at the section top; carbonates are authigenic varieties of the calcite-dolomite series. Modeling of complex XRD profiles reveal Mg-calcite with various Mg contents and excess-Ca dolomites which are mixed-structure crystals compositionally close to stoichiometric dolomite. The crystal structure and relative percentages of carbonates from the dated sedimentary section controlled by climate and lake level changes allow reconstructing the Holocene history of Lake Dolgoe.



10.
FIRST RESULTS OF STUDY OF LAKE BAUNT BOTTOM SEDIMENTS (northern Transbaikalia)

M.A. Krainov1, E.V. Bezrukova1,2, E.V. Kerber1, O.V. Levina1, E.V. Ivanov1, A.A. Shchetnikov3, I.A. Filinov3
1A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
2Institute of Archeology and Ethnography, Siberian Branch of the Russian Academy of Sciences, pr. Lavrentieva 17, Novosibirsk, 630090, Russia
3Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Transbaikalia, lacustrine sediments, Pleistocene, Holocene, paleoclimate, paleomagnetism, excursions, lithology

Abstract >>
In March 2014, the Lake Baunt bottom sediments were drilled in the deepest part of the lake basin (33 m). The penetrated interval is 13.7 m thick, with the age of the base being evaluated at 28-30 ka. Lithological study of the penetrated sediments demonstrates the upper part of the section dominated by diatom ooze, whose concentration decreases gradually downward the section, up to the replacement of the ooze by silty clay. The obtained data on variations in petromagnetic parameters, concentration of biogenic silica, and sediment compaction indicate considerable variations of sedimentary environments during the Late Pleistocene and Holocene. Being compared with the previously reconstructed landscape and climate dynamics for the sedimentary succession of Lake Kotokel for this time interval, the above parameters reveal that the Lake Baunt bottom sediments reliably fix the regional paleoclimate signal. For the first time for lakes of the Baikal region, Gothenburg and Mono Lake magnetic excursions are identified in the paleomagnetic record of the Lake Baunt section.



11.
PREDICTIVE MODELS FOR THE LOCALIZATION OF SOIL LIQUEFACTION IN EARTHQUAKES ON THE MAIN SAYAN FAULT (southern East Siberia)

I.A. Denisenko1,2, O.V. Lunina1
1Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2Irkutsk State Technical University, ul. Lermontova 83, Irkutsk, 664074, Russia
Keywords: Liquefaction, earthquake, faults, prediction

Abstract >>
Predictive models for the localization of soil liquefaction for seismic events with magnitudes MS = 7.5 and 8.0 were constructed based on available data on a possible earthquake in the zone of the Main Sayan Fault. It has been established that for MS = 7.5, liquefaction will extend over a distance of 40 km from the causative seismogenic fault. For MS = 8.0, the limiting distance from the activated segment of the Main Sayan Fault will be 112 km. The calculation models take into account the effect of faults on the predicted process, which allows a more accurate identification of areas with different probabilities of this event. Zones of possible liquefaction at MS = 7.5 include the towns of Kultuk, Sludyanka, Baikalsk, Arshan, and Podkamennaya. At MS = 8.0, the liquefaction process will spread over a large area including the cities of Usole-Sibirskoe, Angarsk, and Irkutsk, especially localities near the Angara River and its major tributaries. Similar evaluation can also be made for other natural situations with known seismogenic faults, fault-block divisibility of the Earths crust for the Pliocene-Quaternary stage of tectonism, earthquake magnitude, and potentially liquefiable soils within the model area.



12.
RECURRENCE OF STRONG SEISMIC EVENTS IN THE AREA OF THE 2011-2012 TUVA EARTHQUAKES ACCORDING TO PALEOSEISMOLOGICAL data

A.N. Ovsyuchenko1, Yu.V. Butanaev2, A.V. Marakhanov1, A.S. Larkov1, S.S. Novikov1, K.S. Kuzhuget2
1O.Yu. Schmidt Earth Physics Institute, ul. Bol. Gruzinskaya 10, str. 1, Moscow, 123242, Russia
2Tuva Institute for Exploration of Natural Resources, Siberian Branch of the Russian Academy of Sciences, ul. Internatsional'naya 117a, Kyzyl, 667010, Russia
Keywords: Earthquake, active tectonics, paleoseismology, seismic focus, seismic regime, Tuva

Abstract >>
The paper presents the results of paleoseismological studies in the epicentral area of the Tuva earthquakes of 2011 ( M = 6.7) and 2012 ( M = 6.8). Their seismotectonic position and seismic history over the last millennia has been studied. The results are of great importance because these earthquakes are the strongest in the history of seismological observations in Tuva and are thus the first well-studied strong earthquakes in this region. The data show that relatively weak events similar to the 2011-2012 Tuva earthquakes recurred every 300-500 years in the past millennium, while catastrophic earthquakes with M = 7.0-7.2 and higher occur approximately every thousand years.



13.
GEOLOGICAL AND GEOPHYSICAL INTERPRETATION OF INDUCED POLARIZATION DATA ON GOLD DEPOITS IN THE YANA-KOLYMA OROGENIC BELT

A.V. Tkachev, I.M. Khasanov, T.I. Mikhalitsyna
N.A. Shilo North-East Interdisciplinary Scientific Research Institute, Far East Branch of the Russian Academy of Sciences, ul. Portovaya 16, Magadan, 685000, Russia
Keywords: Induced polarization, phase frequency response, two-frequency phase parameter graphitization, carbon metasomatism

Abstract >>
This paper presents induced polarization (IP) data on a number of gold deposits and occurrences in the Magadan Region. Geophysical works are effective for the study of gold-quartz deposits of different morphological types (vein, veinlet-vein, and veinlet-disseminated). It is shown that multifrequency IP sounding reliably identifies zones of carbon metasomatism, a reliable indicator of potential gold mineralization areas in northeastern Russia. Carbon metasomatism is the typical shape of phase frequency response curves for graphite and graphitized rocks.



14.
THE CONTRAST SCALE OF MINERALS FOR NEUTRON TOMOGRAPHY OF PALEONTOLOGIC AND GEOLOGIC OBJECTS

A.A. Kaloyan1, E.S. Kovalenko1, A.V. Pakhnevich2, K.M. Podurets1
1National Research Center Kurchatov Institute, pl. Akad. Kurchatova 1, Moscow, 123182, Russia
2Borissiak Paleontological Institute, Russian Academy of Sciences, ul. Profsoyuznaya 123, Moscow, 117647, Russia
Keywords: Tomography, neutrons, X-rays

Abstract >>
Neutron tomography is considered as an alternative to X-ray tomography in the study of paleontologic and geologic objects. Based on experimental data, a contrast scale of minerals and rocks, including those present in paleontologic objects, has been constructed for neutron tomography. Examples of application of neutron tomography of geologic objects are given, and the potentialities of the above methods are compared.



15.
FAST COMPUTATION OF MT CURVES FOR A HORIZONTALLY LAYERED EARTH WITH LATERALLY INHOMOGENEOUS CONDUCTIVITY PERTURBATIONS

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: Magnetotelluric soundings of 3D inhomogeneous earth, static shift, induction distortion, fast algorithm, MT curves, electrical conductivity

Abstract >>
A new algorithm is proposed to compute magnetotelluric (MT) curves for a horizontally layered earth with laterally inhomogeneous conductivity. It is fast and ensures correction of induced eddy currents and galvanic distortions of MT curves produced by 3D inhomogeneities. The computation time is short (~1 min) due to the use of the perturbation method for solving Maxwells equations. The suggested algorithm has a better performance than the more costly classical Trefftz method but has an applicability limitation.