Late Cretaceous rift-related upwelling and melting of the Trindade starting mantle plume head beneath western Brazil

High mantle potential temperatures and local extension, associated with the Late-Cretaceous impact of the Trindade mantle plume, produced substantial widespread and voluminous magmatism around the northern half of the Paraná sedimentary basin. Our previous studies have shown that, above the central and eastern portions of the postulated impact zone where lithosphere extension is minimal, heat conducted by the plume caused large-scale melting of the more fusible parts of the subcontinental lithospheric mantle beneath the margin of the São Francisco craton and the surrounding Brasilía mobile belt. Here we combine geochemical data and field evidence from the Poxoreu Igneous Province, western Brazil to show how more intense lithospheric extension above the western margin of the postulated impact zone permitted greater upwelling and melting of the Trindade plume than further east. Laser ⁴⁰Ar/³⁹Ar age determinations indicate that rift-related basaltic magmas of the Poxoreu Igneous Province were emplaced at ? 84 Ma. Our detailed geochemical study of the mafic magmas shows that the parental melts underwent polybaric crystal fractionation within the crust prior to final emplacement. Furthermore, some magmas (quartz-normative) appear to have assimilated upper crust whereas others (nepheline- and hypersthene-normative) appear to have been unaffected by open-system crustal magma chamber processes. Incompatible trace element ratios (e.g. chondrite-normalised La/Nb?=?1) and isotopic ratios (⁸⁷Sr/⁸⁶Sr?=?0.704 and ¹⁴³Nd/¹⁴⁴Nd?=?0.51274) of the Hy-normative basalts resemble those of oceanic islands (OIB). We therefore propose that these “OIB-like” magmas were predominantly derived from convecting-mantle-source melts (i.e. Trindade mantle plume). Inverse modelling of rare-earth element (REE) abundances suggests that the initial melts were predominantly generated within the depth range of ?80–100 km, in mantle with a potential temperature of ?1500 °C.     

Ophiolite remnants at the eastern margin of the Bohemian Massif and their bearing on the tectonic evolution

Summary Amphibolites are widespread in the eastern part of the Bohemian Massif, east of the South Bohemian Pluton. Based on their geological situation, their metamorphic evolution and their geochemistry, they were separated into three genetically different units: the Rehberg ophiolite, the Buschandlwand amphibolite and the Raabs group. The metamorphic Rehberg ophiolite consists of a ultramafic to mafic plutonic sequence overlain by a gabbro/dike complex and a volcanic section with basaltic, andesitic and rhyolitic volcanics associated with pelitic to psammitic sediments. The entire ophiolite underwent amphibolite facies metamorphism. Rock/MORB normalisation plots and other element ratio plots, such as Ti vs. V or Ta/Yb vs. Th/Yb argue for a supra-subduction zone environment as site of the origin of the Rehberg ophiolite. The Letovice ophiolite in Moravia is structured in a similar way. Geochemically it shows a more MORB like composition but also a distinct tholeiitic island arc group. Although there is no age data for the protolith of both ophiolites, it is believed that they have formed in an oceanic basin separating the Brunovistulian-Moravian block to the east and the Moldanubian block to the west. Possible traces of the continuation of the ophiolites towards the north can be found in the Stare Mesto ophiolites and the ophiolites surrounding the Sowie Gory block in the Sudetes.

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Ophiolitrelikte am ostrand der Böhmischen Masse und ihre bedeutung für die tektonische entwicklung

Zusammenfassung Amphibolite sind in der Böhmischen Masse, östlich des Südböhmischen Plutons weit verbreitet. Ausgehend von ihrer geologischen Position, ihrer metamorphen Entwick lung und ihrer Geochemie lassen sie sich in drei genetisch unterschiedliche Einheiten teilen: den Rehberg Ophiolith, den Buschandlwand Amphibolit und die Raabser Gruppe. Der metamorphe Rehberg Ophiolith besteht aus einer ultramatischen bis mafischen plutonischen Abfolge, die von einem Gabbro/Gangkomplex überlagert wird und einer vulkanischen Folge mit Basalten, Andesiten and Rhyoliten, die mit tonigen und sandigen Sedimenten verknüpft sind. Der gesamte Ophiolithkörper wurde unter amphibolitfaziellen Bedingungen metamorph überprägt. Rock/MORB Diagramme und andere Elementdarstellungen, wie z.B. das Ti vs. V, oder das Ta/Yb vs. Th/Yb Diagramm sprechen für eine Entstehung des Rehberg Ophioliths in einer Suprasubduction Zone. Der Letovice Ophiolith in Mähren weist eine ähnliche Struktur auf. Geochemisch zeigt er stärkere Ähnlichkeiten mit MORB, enthält aber auch Elemente von tholeiitischen Inselbogenbasalten. Auch wenn es für beide Ophiolithe noch keine Protolith-Altersdaten gibt, scheint es dennoch wahrscheinlich, daß sie in einem Ozeanbecken, das den Brunovistulisch-Moravischen Kontinentalblock im Osten vom Moldanubischen Kontinent im Westen trennt, gebildet wurden. Die mögliche Fortsetzung beider Ophiolithe könnten im Norden der Stare Mesto Ophiolith und die Ophiolithe rund um den Sowie Gory Block in den Sudeten darstellen.

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With 7 Figures     

The economic restructuring of Moscow in the international context

This paper deals with the trends of economic restructuring in Moscow in the 1990s under globalization and reforms. The comparison of structural shifts in Moscow with the largest cities of the West gives an idea about the position of the Russian capital on the trajectory of post-industrial transformation. The analysis covers three dimensions: a) general trends of post-industrial restructuring, b) the role of large cities in national economies, and c) universal and special trends of intra-urban transformation. The reforms of the 1990s initiated many new developments in the economic life of Moscow, making it more similar to the Western cities, both in general sectoral structure and intra-urban landscape. Nevertheless, Moscow still lags far behind the world cities as regards the stage of the most important post-industrial processes. The conflict between new market developments and the inherited patterns of the socialist city becomes one of the driving forces of the economic transformation in Moscow as a whole and in different types of its districts.     

THE IMPORTANCE OF TOPOGRAPHIC CORRECTIONS ON MAGNETOTELLURIC RESPONSE DATA FROM RUGGED REGIONS OF ANATOLIA

Topographic irregularities cause some distortions of magnetotelluric (MT) fields. In the vicinity of a topographic feature, the TM-mode distortion increases with the height and inclination of the slope. It is well-known that TM-mode ( E _⊥) topographic effects are much greater than TE-mode ( E _ı) distortions.   We have made a study of MT anomalies in TM-mode due to two-dimensional topography. In order to reduce these effects, the distortion tensor stripping technique was used. After corrections, the resulting data can be interpreted as if they were obtained over a flat surface and depend only on the subsurface structure. However, this technique sometimes causes some geometrical distortions of the real subsurface structure.   One of our aims is to overcome this failure. We have modified the correction coefficients by considering the actual one-dimensional geology. Model studies showed that our approach is especially useful in removing the terrain effects on complex 2D subsurface structures.   The other purpose of this study is to emphasize the importance of a proper terrain correction for data from sites having mountainous topography over complex geology, e.g. strike-slip faults, suture zones and rift valleys. Some examples of MT data sets collected from the North Anatolian Fault Zone and from the thrust regions of the Western Taurides will be presented.     

Untersuchung der Sorptionseigenschaften des Kationenaustauschers KB-2M mit Makronetzstruktur zur Abtrennung von Zinkionen aus Ab- und Spülwässern

Study of Sorptional Properties of the Cation Exchanger KB-2M with Macroreticular Structure for Recovery of Zinc Ions from Sewage and Rinsing Water Although a number of ion-exchange methods have been employed for the recovery of some transition metals from industrial effluents, knowledge about ion-exchange resins with macroreticular structure is poor. The present paper describes the mechanism of sorption on such exchangers and their application for recovery of zinc from sewage rinsing water. Ion exchanger of macroreticular structure are polymers with long-chained cross-linking agents. We have synthesized carboxylic ion-exchange resins by hydrolysis of copolymerisates of methyl acrylate with different cross-linking agents: divinylbenzene, divinyl sulfide, divinyl ester of ethylene glycol and divinyl ester of di- or triethylene glycol. The sorption process on modifications of the carboxylic resins KB-2 of various structure was studied with different methods: potentiometric titration, infrared spectroscopy, electron microscopy, X-ray structural analysis. The initial zinc concentration in rinsing water was 0.05 mol/L at pH from 3 to 6. For the sorption, 0.2…1.0 g of resin were equilibrated with 100 mL of zinc solution. After equilibrium (12 h), the resin was separated from solution. The zinc ions were determined by atomic absorption spectrometry after stripping with 100 mL of 10% sulfuric acid. The distribution ratio D was calculated (D: mmole of Zn sorbed per gram of resin divided by mmole of Zn per millilitre of solution). By means of infrared spectroscopy, the mechanism of sorption of zinc ions from rinsing water was determined. There may be a possibility of the formation of complexes in the cation-exchange resin phase. It was found out in this paper that the cation-exchanger KB-2M of macroreticular structure is the most effective for the sorption of the Zn²⁺-ions from sewage and rinsing water.     

Influence of the total atmospheric optical depth and cloud cover on solar irradiance components

Broadband solar irradiance data obtained in the spectral range 400–940 nm at Kwangju, South Korea from 1999–2000 have been analyzed to investigate the effects of cloud cover and atmospheric optical depth on solar radiation components. Results from measurements indicate that the percentage of direct and diffuse horizontal components of solar irradiance depend largely on total optical depth (TOD) and cloud cover. During summer and spring, the percentages of diffuse solar irradiance relative to the global irradiance were 5.0% and 4.9% as compared to 2.2% and 3.0% during winter and autumn. The diffuse solar irradiance is higher than the direct in spring and summer by 24.2%, and 40.6%, respectively, which may largely be attributed to the attenuation (scattering) of radiation by heavy dust pollution and large cloud amount. In cloud-free conditions with cloud cover ≤2/10, the fraction of the direct and diffuse components were 66.0% and 34.0%, respectively, with a mean daily global irradiance value of 7.92±2.91 MJ m⁻² day⁻¹. However, under cloudy conditions (with cloud cover ≥8/10), the diffuse and direct fractions were 97.9% and 2.2% of the global component, respectively. The annual mean TOD under cloudless conditions (cloud cover≤2/10) yields 0.74±0.33 and increased to as much as 3.15±0.67 under cloudy conditions with cloud amount ≥8/10. An empirical formula is derived for estimating the diffuse and direct components of horizontal solar irradiance by considering the total atmospheric optical depth (TOD). Results from statistical models are shown for the estimation of solar irradiance components as a function of TOD with sufficient accuracy as indicated by low standard error for each solar zenith angle (SZA).     

Numerical Modeling of Ice Jams

A numerical model is proposed to describe the formation of ice jams under the effect of a release wave.     

Study of Heavy Metal Compound Transformations in Surface Waters

Results of studying Fe(III) hydrolysis and sorption of heavy metal compounds by organic matter of bottom sediments are discussed. The rate of Fe(III) hydrolysis is found to be largely determined by the concentration of dissolved organic substances. Values of kinetic parameters are obtained for heavy metal compounds sorption under static and dynamic conditions. Calculating the solubility of Fe, Cu, Cd, Zn, and Pb sulfides allowed the assessment of the amount of metals lost by bottom sediments due to the formation of metal complexes with dissolved organic substances contained in natural waters.     

Geographical and Ecological Characteristics of the Caspian Sea and Modern Tendencies in the Evolution of Its Ecosystem

The Caspian Sea is characterized in the geographic and ecological aspects, and the state of its ecosystem is estimated. The natural and anthropogenic processes that control the formation of the environmental conditions in the Caspian Sea and the distribution of principal commercial hydrobionts and their food items are analyzed. Data on modern tendencies in changes in the abiotic and biotic parameters of the ecosystem, their causes and mechanisms are summarized. Prospects of further changes related to the development of shelf fields of petroleum hydrocarbons are assessed.     

Nutrient Transport into the White Sea with River Runoff

Averaged data from long-term observations of concentrations of mineral-nutrient fractions along with fragmentary data and indirect estimates of organic-component concentrations in the tributaries of the sea (the Niva, the Onega, the Northern Dvina, the Mezen, and the Kem rivers) are analyzed. Monthly variations in the concentrations of the major nutrients in the river water flowing into the sea are characterized, and relationships between them in different seasons are determined. Annual nutrient transport into the White Sea by river water is assessed based on characteristics of river runoff and nutrient concentrations using a mathematical model. Wide variations are established in the ratios of organic and mineral fractions of nutrients delivered into the sea. The shares of mineral components in the total runoff of N_tot and P_tot into the sea are found to be equal to 18.1 and 18.8%, respectively.