Extensional tectonics and mid-Paleozoic massive sulfide occurrences in Europe

The age and lithologic settings of mid-Paleozoic massive sulfide deposits in Central Europe and southwest Iberia are suggestive of extensional tectonic environments. This inference is supported by the facies configurations of contemporaneous clastic sediments, the presence of deepwater lithologies and pelagic faunas, and marked mafic-felsic bimodalism in associated volcanic rocks.The massive sulfide deposits of the Moravia-Silesia area, Rammelsberg, Meggen, and other deposits appear to have formed in the same tectonic environment: one dominated by crustal extension. The important massive sulfide deposits of the southwest Iberian province formed somewhat later, but appear to be related to a phase of crustal extension initiated in late Devonian time.These two sets of rifting (sensu latu) events correlate in time with Caledonide collision in the north and subsequent Acadian collision further south. The postulated extensional events thus may relate directly to these collisions.All the areas under consideration were subsequently affected by Hercynian compressional events. The high potash granites associated with Hercynian collisions are largely the products of crustal melting and consequently have associated with them ore deposits characterized by lithophile elements such as tin, tungsten and uranium. A significant fraction of the Paleozoic metallogeny of Europe can thus be understood in terms of extensional tectonic events followed by compressional events less than 100 m.y. later.

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Zusammenfassung Das Alter und die lithologische Zusammensetzung von massiven Sulfiderzlagerstätten des Devons in Mittel-Europa und Südwest-Iberien deuten auf eine Ausweitungstektonik. Diese Hypothese wird bekräftigt durch die Fazieskonfiguration gleichalter klastischer Sedimente, das Auftreten von Tiefseeablagerungen und pelagischen Faunen, und die ausgesprochen mafisch-felsische Bimodalität von assoziierten Vulkaniten.Die massiven Sulfidlagerstätten von Mähren und Schlesien, Rammelsberg, Meggen und andere Vorkommen scheinen sich unter den gleichen tektonischen Bedingungen gebildet zu haben, nämlich unter Dehnungseffekten der Kruste. Die wichtigsten massiven Sulfidlagerstätten der südwestlichen Iberischen Provinz entstanden etwas später, sie scheinen einer Dehnungsphase beginnend im höheren Devon zugeordnet zu sein.Diese zwei Phasen eines Riftings (sensu lato) stimmen zeitlich mit der kaledonischen Kollision im Norden und der darauffolgenden akadischen Kollision weiter südlich überein. Die angenommenen Dehnungsvorgänge können daher direkt mit diesen Kollisionen in Verbindung gebracht werden.Alle besprochenen Gebiete sind in der Folge von herzynischen Einengungs-Erscheinungen betroffen worden. Die hochgradig kali-haltigen Granite, die den herzynischen Kollisionen zugeordnet sind, sind größtenteils die Ergebnisse von krustalen Schmelzvorgängen und haben deshalb assoziierte Erzlagerstätten, die durch lithophile Elemente wie Zinn, Wolfram und Uran gekennzeichnet sind. Ein beträchtlicher Teil der paläozoischen Metallogenese Europas kann daher aus der Sicht distraktiver tektonischer Erscheinungen gesehen werden, deren Einengungs-Vorgänge weniger als 100 Millionen Jahre später folgten.

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Résumé L'âge et la composition lithologique des gisements de sulferes massifs du Paléozoïque moyen de l'Europe Centrale et du sud-ouest de la Péninsule ibérique suggèrent un environement tectonique de distension. Cette hypothèse est appuyée par la configuration des facies des sédiments clastiques contemporains, la présence de lithologies d'eau profonde et de faunes pélagiques et par l'existence d'un net bimodalisme mafique-felsique dans les roches volcaniques associées.Les importants gisements de sulfere de Moravie et de Silésie, du Rammelsberg, de Meggen et autressemblent s'être formés sous un régime tectonique semblable, principalement sous l'effet de distensions de la croûte. Les gisements du sud-ouest de la Péninsule ibérique se sont formés un jeu plus tard, mais semblent être liés à une phase de distension crustale ayant débutéau Dévonien supérieur.Ces deux séries de ruptures (sensu latu) sont corrélés dans le temps avec la collision calédonienne au nord et la collision acadienne subséquente plus au sud.Les évènements de distension invoqués peuvent done être directement liés à ces collisions.Toutes les régions considérées ici furent affectées plus tard par la compression hercynienne. Les granites à haute teneur en potasse, liés aux collisions hercyniennes sont, en grande partie, des produits de la fusion crustale. Ils sont par conséquent associés à des gisements de minerais d'étain, de tungstène et d'uranium. Une partie importante de la métallogénie paléozoïque de l'Europe peut être ainsi comprise en termes d'événements tectoniques de distensions suivis moins de 100 millions d'années plus tard, par une compression.

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Atmospheric circulation climate changes

The role of the atmospheric circulation in climate change is examined. A review is given of the information available in the past record on the atmosheric circulation and its role in climate change, firstly at the surface via sea level pressure in both the northern and southern hemispheres and secondly for the free atmosphere. As with most climate information, the climate record is compromised by non-physical inhomogeneities arising from changes in observing and analyzing techniques and changes in data coverage. Problems with and threats to the rawinsonde network are discussed. Global analyses produced by the operational centers, U.S. National Meteorological Center (NMC) and the European Centre for Medium Range Weather Forecasts (ECMWF), for weather forecasting purposes contain many discontinuous changes in the analyses arising from improvements in the system used to produce them. A discussion is given of the prospects for and motivation behind an activity known as reanalysis in which the historical data are reanalyzed using a state-of-the-art system that is held constant for the entire record. The only sources of spurious change then are the changes in the observing system, such as the introduction of space-based observations. Recommendations are made on needed actions for better understanding and monitoring climate change.The role of the atmospheric circulation and the strong links to other variables such as temperature, precipitation and wind are established and illustrated with a survey of decadal variability, the evidence for it, and the way in which the observed atmospheric circulation is involved in the Pacific and Atlantic sectors. The importance of teleconnections is stressed, especially in the winter half year, for understanding local climate change. The likelihood that changes will be manifested in the frequency and intensity of preferred modes of behavior in the atmosphere, such as the El Niño-Southern Oscillation and Pacific-North American teleconnection patterns, rather than in changes in the modes is also emphasized. The recently observed climate changes and the tendency for an unprecedented prolonged El Niño are interpreted in this framework. The key coupled atmosphere-ocean character of decadal variability is noted with the atmosphere providing the spatial scales, the ocean the memory, but also with the need for collaborative, as opposed to destructive, interactions through the atmospheric circulation.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The solubility control of rare earth elements in natural terrestrial waters and the significance of PO 4 3− and CO 3 2− in limiting dissolved rare earth concentrations: A review of recent information

Rare earth element (REE) concentrations in alkaline lakes, circumneutral pH groundwaters, and an acidic freshwater lake were determined along with the free carbonate, free phosphate, and free sulfate ion concentrations. These parameters were used to evaluate the saturation state of these waters with respect to REE phosphate and carbonate precipitates. Our activity product estimates indicate that the alkaline lake waters and groundwaters are approximately saturated with respect to the REE phosphate precipitates but are significantly undersaturated with respect to REE carbonate and sulfate precipitates. On the other hand, the acidic lake waters are undersaturated with respect to REE sulfate, carbonate, and phosphate precipitates. Although carbonate complexes tend to dominate the speciation of the REEs in neutral and alkaline waters, our results indicate that REE phosphate precipitates are also important in controlling REE behavior. More specifically, elevated carbonate ion concentrations in neutral to alkaline natural waters tend to enhance dissolved REE concentrations through the formation of stable REE-carbonate complexes whereas phosphate ions tend to lead to the removal of the REEs from solution in these waters by the formation of REE-phosphate salts. Removal of REEs by precipitation as phosphate phases in the acid lake (pH=3.6) is inconsequential, however, due to extremely low [PO ₄ ^3– ] _F concentrations (i.e., 10^–23 mol/kg).     

Late holocene paleoclimatic and paleobiologic records from sediments of Devils Lake,North Dakota

An 84 cm sediment core collected from the center of Devils Lake, North Dakota, was analyzed at 1-cm intervals for,²¹⁰Pb,¹³⁷Cs, sediment conductivity, the concentrations of, biogenic silica, total organic carbon, carbon to nitrogen ratio, and the carbon and nitrogen isotopic composition of the organic fraction. Variations in²¹⁰Pb activities in the upper 20 centimeters indicate that sediment accumulations rates in Devils Lake are not constant, and that accumulation rates were highest during periods of high lake level. The mean sedimentation accumulation rate was calculated as 0.24 cm^–1 yr. The¹³⁷Cs profile is characterized by near-surface maximum concentrations, possibly the result of redistribution of¹³⁷Cs during salinity excursions.Biogenic silica is strongly correlated to lake level in Devils Lake. Periods of low lake level (characterized by high sediment conductivity) correspond to low biogenic silica concentrations. The trends in biogenic silica are attributed to variations in diatom productivity in the lake and to variations in sediment accumulation rates. Based on biogenic silica content and the composition of organic matter in the sediment (total organic carbon, carbon:nitrogen ratio and the ¹³C and ¹⁵N composition of total organic matter), paleobiologic conditions of Devils Lake during low lake stands were characterized by, (1) decreased primary productivity, (2) decreased input of detrital organic matter, and (3) increased nitrogen availability.During the 350 years of sediment accumulation represented by the 84-cm sediment core Devils Lake has experienced two periods of sustained high lake level; one between about 130 and 170 years ago (1820 to 1860 A.D.) and the second between 270 and 310 years ago (1680 to 1720 A.D.). Devils Lake experienced a period of intense drying about 260 years ago (1720 A.D.).     

A multi-term trial function stability analysis of isotropic relativistic star clusters

A multi-term trial function technique is developed for studying the dynamic stability of isotropic relativistic star clusters by using the variational principle originated by Ipser and Thorne (1968). The technique is applied ton=4 polytropic clusters, and low-temperature isothermal clusters. These two types of cluster have pronounced core-halo structures and they have both proved difficult to analyse with single-term trial function methods. Then=4 polytropic clusters are proved to be dynamically unstable if their central redshifts are greater thanz _c=0.412. This is quite close to the point on their sequence withz _c=0.41, where their fractional binding energy peaks. Strong evidence is obtained that all isothermal clusters with no dispersion in the stellar rest mass become dynamically unstable near the region where their fractional binding energy peaks, and that none of these clusters is dynamically stable if their central redshift exceedsz _c0.53.     

Influence of UV-B Radiation and Temperature on Photodegradation of PAHs: Preliminary Results

The joint impact of UV-B radiation and temperature on photodegradation of polycyclic aromatic hydrocarbons (PAHs) sorbed to an organic solvent was assessed in this study. This approach was experimentally performed in a laboratory investigation by means of comparison of two different environments: Atlantic (Lancaster, UK) and Mediterranean (Tarragona, Catalonia, Spain) climatic conditions. The concentration of 10 PAHs contained in a tetradecane solution was compared under two different temperatures (10 and 20°C) and UV-B doses (6.5 and 22.5 kJ m⁻² day⁻¹). No photodegradation was observed for the heaviest hydrocarbons (benzo(a)anthracene, chrysene, benzo(a)pyrene, dibenzo(g,h,i)perylene and coronene). In general terms, the half-life of PAHs was highly dependent on their molecular weight. Significant faster photodegradation rates were detected specially for light PAHs. It indicates that a synergistic effect occurred when both temperature and UV-B dose increased. This synergism might have a great implication on the long-range transport of environmental organic pollutants taking into account that low-latitude areas are the hottest and most irradiated of the planet.