Die Genese der stratiformen Sulfidlagerstätte Kalwang (Steiermark), der Grünsteinserie und einer assoziierten silikatreichen Eisenformation

Zusammenfassung Die bearbeitete Lagerstätte ist dem Typ submarin exhalativer Bildung zuzuordnen. Grünschiefermetamorphe Nebengesteine (ehemalige vulkanosedimentäre Abfolge) unterlagenin situ einer hydrothermalen Alteration. Metallösungen (hot brines), welche zur Bildung der Sulfidlager führten, eruptierten im Bereich submariner Fumarolen. Sie entstammten Interaktionen meteorischer Wässer mit vulkanogenen In- und Extrusivprodukten. Die Lösungen bildeten schichtgebundene Erzlager, die zoniert als hoch-bis niedrigtemperierte Bildung vorliegen. Eine assoziierte silikatreiche Eisenformation schließt die Vererzung sowie die vulkanische Tätigkeit ab. Die Grüngesteine werden als Metabasite kontinentaler bis ozeanbodentholeiitischer Edukte gedeutet. Hinsichtlich der geotektonischen Situation verweisen alle Merkmale auf das Milieu einer MORB-Typ assoziierten, alterationsbedingten sulfidischen Vererzung als Folgeprodukt zunehmender Ozeanisierung eines kontinentalen Riftbereiches.

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Genesis of the Kalwang stratiform sulphide deposit, Styria, Austria, and of associated metavolcanics and siliceous banded iron formation

Summary The Kaiwang copper deposit (Styria, Austria) occurs within a Lower Paleozoic volcanosedimentary sequence which forms part of the extensive Nördliche Grauwackenzone of the Eastern Alps. Stratiform bodies of pyrite (0.02–0.05% Ni; 0.05–0.08%Co)-chalcopyrite and (Ni,Co-free) pyrrhotite-chalcopyrite ores are associated with mafic metavolcanic rocks; metapelites and marbles are also present in the ore environment. Comprehensive analyses of major and trace elements suggest that the metavolcanites have been derived from tholeiites of intraplate-to ocean floor affinity linked to the development of an intracontinental rift. Regional metamorphism of lower greenschist grade was preceded by spilitization of the volcanic rocks. Mineralization at Kalwang is submarine-exhalative; some copper sulphides have been deposited in supply channels prior to reaching the sea floor. Towards the hanging-wall, the ore-bearing sequence is terminated by a two metres thick manganiferous iron formation; manganese is concentrated almost exclusively in spessartine garnet. The BIF has been derived from a manganiferous, chamositic precursor sediment. Stratabound base metal deposits further west in the Northern Greywacke Zone show similar evolutionary trends; this points towards a coherent metallogenetic pattern for this important tectonic unit.

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Mit 12 Abbildungen     

Salt efflorescences and Saline lakes; a distributional analysis

Salt lakes and salt efflorescences are a common phenomenon of many arid zones. Rocks weather rapidly in the presence of saline materials, and the rate of such weathering may be controlled by the mineralogy of the salts concerned. The distribution of the main salt types is presented for the polar deserts of Antarctica and the Arctic, and for the warmer deserts of Australia, North America, South America, Africa and Asia. There is great variety in the types of salts encountered and marked differences between different regions, with, for example, Australia being dominated by sodium chloride (halite) and southern Canada by the sulphates of magnesium and sodium. The possible causes of such variability and its pattern are analysed in terms of the nature of inputs into drainage basins and the various changes that take place within basins. Finally, it is apparent that in those situations when weathering has been observed as an active process there are a great many different salts involved.     

The winterstorm “Vivian” of 27 February 1990: About the meteorological development,wind forces and damage situation in the forests of Switzerland

Summary During the months January and February 1990 a series of severe cyclones were responsible for enormous wind-induced damage in Europe. The final of this series, on 27 February 1990, cyclone Vivian mainly affected the alpine valleys of Switzerland. 5 Millions m³ of timber were felled by the severe winds, a record number in this century. A complete damage survey of the deforested areas offers in combination with meteorological data an unique data set for a detailed case study of this extreme event.This paper describes the general meteorological development from the synoptic scale down to the mesoscale of Switzerland and presents a general overview of the damage situation. The main results show that a rare situation of a straight frontal zone stretching over the whole Atlantic Ocean and showing a strong gradient in temperature pointed directly toward Central-Europe. Two waves formed along this elongated polar front and deepend rapidly to depressions. The first low travelled on the southernmost trajectory of the whole storm series and affected Switzerland most. North of the Alps the prefrontal warm air was blocked to the east by the arriving coldfront and had to escape into the complex terrain of the alpine valleys. There, the stormy winds were strengthened by channelizing and Föhn effects. The large temperature gradient between the prefrontal and the incoming air masses induced thunderstorm activity which vortices and downdrafts might have enhanced locally. As a result most of the damaged forested areas were found between 1200 and 1600 m MSL on slopes, which were mainly exposed toward the prevailing NW-winds. A comparison of extreme wind speeds for the period 1978–1992 revealed that this event's extreme high speed of 74.5 m/s, measured at a high elevated pass station in the mountains, was exceptional. For lower elevated stations the wind speeds were high but in the range of other observed extreme values. In addition to the severe wind forces the duration of sustained high wind speed was exceptionally long during February 1990.With 16 Figures     

Isotope evidence for ijolite formation by fenitization: Sr−Nd data of ijolites from the type locality Iivaara,Finland

Ijolites from the type locality at Iivaara, Finland, form a continuous series of magmatic rocks ranging from urtites to melteigites. Both Ni and Cr, but also the large ion lithophile light-rare-earth elements, Zr, Hf, Nb, Rb, Sr and Ba are low in concentration. The Nd contents equal those of the neighboring fenites, Sr is distinctly less abundant, and there is no significant Eu anomaly. The ¹⁴³Nd/¹⁴⁴Nd and ⁸⁷Sr/⁸⁶Sr of the ijolites demonstrate a systematic covariation between the data of carbonaties from the Kola Alkaline Province (_Sr – 13.8, _Nd + 5.6) and those of the fenites at Iivaara (_Sr + 132.9, _Nd – 24.7) with _Sr varying from +0.3 to +23.9 and _Nd varying from-9.2 to-19.3. The trace element abundances and the isotopic data give evidence for a crystallization of the rocks from a liquid generated by melting (rheomorphism) of high-grade fenitized country rocks rather than from a primary mantle-derived magma which was contaminated at crustal levels. The fenitization of wall rocks preceding the ijolite magma formation was clement selective. Mixing of elements during the fenitization process between the designated components carbonatite (or derivative fenitizing fluid) and wall rock should have been dynamical depending on the stability of the wall rock mineral assemblages in contact with the fenitizing fluids, the migration velocity of these fluids, and their capacity of the respective elements. Such dynamical mixing explains best the variation of the isotope ratios withont systematic covariation of the respective element concentrations.     

Numerical simulation of turbulent convective flow over wavy terrain

By means of a large-eddy simulation, the convective boundary layer is investigated for flows over wavy terrain. The lower surface varies sinusoidally in the downstream direction while remaining constant in the other. Several cases are considered with amplitude up to 0.15H and wavelength ofH to 8H, whereH is the mean fluid-layer height. At the lower surface, the vertical heat flux is prescribed to be constant and the momentum flux is determined locally from the Monin-Obukhov relationship with a roughness lengthz _o=10^–4 H. The mean wind is varied between zero and 5w _*, wherew _* is the convective velocity scale. After rather long times, the flow structure shows horizontal scales up to 4H, with a pattern similar to that over flat surfaces at corresponding shear friction. Weak mean wind destroys regular spatial structures induced by the surface undulation at zero mean wind. The surface heating suppresses mean-flow recirculation-regions even for steep surface waves. Short surface waves cause strong drag due to hydrostatic and dynamic pressure forces in addition to frictional drag. The pressure drag increases slowly with the mean velocity, and strongly with /H. The turbulence variances increase mainly in the lower half of the mixed layer forU/w _*>2.     

Limiting wave growth for electron cyclotron waves

Quasilinear weak diffusion theory presented by Kennel and Petschek (1966) and advanced by Schulz and Davidson (1988) is further extended to put an upper limit on the growth of electron cyclotron waves. It is shown that the power gain of whistler mode electron cyclotron wave (other than plasmaspheric hiss) can not exceed 40 dB. Inside the outer radiation belt, the upper limit of temporal wave growth is 350 rad s^–1 and normalised wave growth is 0.017. The limits are independent of the kind of the electron diffusion and are applicable for on the equator/off the equator locations of wave-particle interactions.     

The vorticity and angular momentum budgets of Asian summer monsoon

The study delineates the vorticity and angular momentum balances of Asian summer monsoon during the evolution and established phases. It also elucidates the differences between these balances in the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis and the National Centre for Medium Range Weather Forecasts (NCMRWF) analysis fields. The NCEP/NCAR reanalysis for a 40 year period (1958-97) and the NCMRWF analysis for a three year (1994-96) period are made use of for the purpose. The time mean summer monsoon circulation is bifurcated into stable mean and transient eddy components and the mean component is elucidated. The generation of vorticity due to stretching of isobars balances most of the vorticity transported out of the monsoon domain during the evolution period. However, during the established period, the transportation by the relative and planetary vorticity components exceeds the generation due to stretching. The effective balancing mechanism is provided by vorticity generation due to sub-grid scale processes. The flux convergence of omega and relative momenta over the monsoon domain is effectively balanced by pressure torque during the evolution and established phases. Nevertheless, the balance is stronger during the established period due to the increase in the strength of circulation. Both the NCMRWF and NCEP fields indicate the mean features related to vorticity and angular momentum budgets realistically. Apart from the oceanic bias (strong circulation over oceans rather than continents), the summer monsoon circulation indicated by the NCEP is feeble compared to NCMRWF. The significant terms in the large-scale budgets of vorticity and angular momentum enunciate this aspect     

Influence of southern oscillation and SSTs over Nino-3.4 region on the winter monsoon rainfall over coastal Andhra Pradesh

An analysis of the mean monthly data of 124 years reveals that the relationship between the Southern Oscillation Index in September and the winter monsoon rainfall (WMR) over Coastal Andhra Pradesh (CAP) is variable and non-stationary. In the recent four decades, however, SOI (Sept) is negatively and significantly correlated with CAP WMR. A similar analysis is performed using 50 years of mean monthly SSTs over Nino-3.4 region in August and September and CAP WMR to detect a possible relationship and there is a striking positive relation between them. In both of the above cases, the September signal is more significant in the recent four decades than for the other months and seasons for probable prediction of CAP WMR. Finally, to examine the influence of SO on the winter monsoon rainfall, a non-parametric test “Mann-Whitney Rank Statistics” test has been applied to the rainfall associated with extreme positive and negative SOI events     

Implications of climatic variability and climate change for water resources availability and management in West Africa

The paper examines: (a) trends in climatic variations and variability with particular emphasis on rainfall (b) the characteristics of climatic events, including floods and droughts, (c) seasonal variations in river flows, (d) mean annual trends in river flows and discharges, (e) local variations of extremes of rainfall and river discharges, (f) the effects of climatic variability and climate change on ground water variations, (g) the problems of acute shortage of freshwater, and (h) the prevalence of water stress whose characteristics would be worsened with the projected impacts of climate change. The results show that: (i) there are a lot of spatial and temporal variations in the characteristics of rainfall and the hydrological systems locally and regionally, although in general, there have been downward trends in rainfall and increases in water deficits and drought events, (ii) that flood events, which also have impacted adversely in many parts of the region, have also been witnessed. The paper then produces projections for future urban and rural water supplies in Nigeria, which is an epitome of West Africa and examines the two main categories of adaptation measures needed to improve water management, namely, those involving the water supply and water demand systems in the study region. Finally, the paper discusses the need to address a number of mechanisms for implementation of the various adaptation measures including: (a) building capacity and manpower, (b) promoting education and public awareness, (c) public participation and the involvement of stakeholders, (d) the establishment of both national and regional co-operation, and (e) the need for climatic and other environmental data collection and monitoring. This revised version was published online in July 2006 with corrections to the Cover Date.     

Loss of orbital angular momentum in close binary systems during their evolution

A total 91 binary systems of systemic mass less than 6.5M have been studied. It is found that binary systems obey the relation: logH=C–1.8 logM whereC is constant having values –1.18, –2.12 and –2.27 respectively for detached, semi-detached and contact binary systems. It is inferred that during evolution, the systemic orbital angular momentum decreases.