Isotopic datings of reddish granitoids in southern Värmland,southwestern Sweden

Three reddish granites from the Gneiss Complex of south-western Sweden have been dated with the U-Pb and one of them also with the Rb-Sr method. The Gneiss Complex consists of two mega-units separated by a tectonic discontinuity. The two granites from the western mega-unit (»the Western Gneiss Segment«) yield zircon upper-intercept ages of 1552 _–36 ⁺³⁸ and 1499 _–36 ⁺³⁶ Ma (2). These ages are minimum estimates of the intrusion ages, but the difference between the obtained and the true age is probably small. This assumption is based on studies of the morphology and internal structures of the zircons and also on air abrasion experiments.The third granite is located in the eastern mega-unit (the »Eastern Gneiss Segment«) and forms a number of small massifs, 50 m in diameter. The U-Pb and Rb-Sr ages agree within the limits of the errors — 1140 _–52 ⁺⁵⁴ Ma (upper intercept) and 1104 ± 100 Ma, respectively — but the obtained age is nevertheless dubious. Thin-section studies reveal that the zircons are heterogeneous with different types of material making up the inner and outer parts. Electron-microscopic studies as well as air abrasion and leaching experiments were performed to establish possible differences in age and chemistry between the inner and outer parts. The central parts are made up of almost pure ZrSiO₄ whereas the outer parts are layered with alternating pure ZrSiO₄ layers and layers rich in trace elements. The leaching and air abrasion data do not indicate any age difference between the inner and outer parts. This supports the validity of the upper-intercept age as an intrusion age.The Rb-Sr age is questionable since the obtained initial⁸⁷Sr/⁸⁶Sr ratio is as low as 0.7027. This cannot possibly be true for a felsic, late Proterozoic granite. A plausible explanation could be a rotation of the isochron due to migration of Rb and Sr during a low-grade event. This event is also responsible for the alteration of the biotites and plagioclases.These data provide additional evidence for extensive ensialic magmatism in the period succeeding the lithosphere-forming event.

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Zusammenfassung Drei rötliche Granite aus dem Südwestschwedischen Gneiskomplex sind mit der U-Pb Methode und einer davon zusätzlich mit der Rb-Sr Methode datiert worden. Der Gneiskomplex besteht aus zwei Haupteinheiten, die tektonisch voneinander getrennt sind. Zwei Granite aus der westlichen Haupteinheit (dem sogenannten »Western Gneiss Segment«) ergeben obere Schnittpunktsalter der Zirkone von 1552 _–36 ⁺³⁸ bzw. 1499 _–36 ⁺³⁶ Ma (2). Diese Alter stellen Minimumalter für die Instrusionen dar, die nur geringfügig jünger sind als die wahren Instrusionsaltern. Diese Vermutung stützt sich auf Untersuchungen der Morphologie und der internen Struktur der Zirkone sowie auf Experimente mit Hilfe der Luftabriebstechnik (air abrasion technique).Der dritte Granit stammt aus der östlichen Haupteinheit (dem sogenannten »Eastern Gneiss Segment«), in der er kleine Körper von etwa 50 m Durchmesser bildet. Die U-Pb und Rb-Sr Alter von 1140 _–52 ⁺⁵⁴ Ma (oberer Schnittpunkt), bzw. 1104 ± 100 Ma stimmen innerhalb des Fehlers überein. Trotzdem ist dieses Alter fragwürdig. Dünnschliffuntersuchungen zeigen, da\ die Zirkone heterogen sind, und da\ Rand und Kern unterschiedlich zusammengesetzt sind. Um Unterschiede in Alter und Chemismus zwischen Rand und Kern festzustellen, wurden Untersuchungen mit dem Elektronenmikroskop, Luftabriebsexperimente und Anätzexperimente durchgeführt. Die Kerne bestehen fast aus reinem ZrSiO₄, wogegen die äu\eren Ränder aus Wechsellagerungen von reinem ZrSiO₄ und Lagen mit hohem Spurenelementgehalt bestehen.Die Anätzversuche und die Luftabriebsexperimente brachten keinen Altersunterschied zwischen Rand und Kern. Diese Tatsachen sprechen dafür, da\ das obere Schnittpunktsalter dem Instrusionsalter entspricht.Das Rb-Sr Alter ist fragwürdig, zumal das⁸⁷Sr/⁸⁶Sr-Initialverhältnis einen sehr niedrigen Wert von 0,7027 aufweist, der für einen spätproterozoischen Granit viel zu niedrig ist. Eine mögliche Erklärung ist die Rotation der Isochrone wegen einer Migration von Rb und Sr während eines Ereignisses bei niedriger Temperatur, ein Ereignis, das auch für die Umwandlung von Biotit und Plagioklas verantwortlich zu sein scheint. Die oben aufgeführten Daten geben zusätzliche Hinweise für einen sialischen Magmatismus im Zeitraum des fortschreitenden Ereignisses der Bildung der Lithosphäre.

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Résumé Trois granites rougeâtres provenant du complexe gneissique du sud-ouest de la Suède ont été datés par la méthode U-Pb et, pour l'un d'entre eux, également par la méthode Rb-Sr. Le complexe gneissique consiste en deux grandes unités séparées par une discontinuité tectonique. Les zircons de deux granites provenant de l'unité occidentale (»Western Gneiss Segment«) fournissent des âges (intersection supérieure) de 1552 _–36 ⁺³⁸ et 1499 _–36 ⁺³⁶ Ma (2). Ces âges constituent des estimations minimales des âges d'intrusion, la différence entre l'âge mesuré et l'âge véritable étant probablement minime. Cette supposition se base sur l'étude de la morphologie et des structures internes des zircons, ainsi que sur des expériences d'abrasion à l'air.Le troisième granite est situé dans l'unité orientale (»Eastern Gneiss Segment«) et se présente en plusieurs massifs d'une cinquantaine de mètres de diamètre. Les âges U-Pb et Rb-Sr coÏncident dans les limites des erreurs (1140 _–52 ⁺⁵⁴ (point d'intersection supérieur) et 1104±100 Ma) l'âge obtenu étant néanmoins incertain. L'étude en coupes minces montre que les zircons sont hétérogènes, leurs parties centrales et périphériques présentant des constitutions différentes. Des examens au microscope électronique, ainsi que des essais d'abrasion à l'air et de corrosion à l'acide ont eté effectués afin de mettre en évidence des différences éventuelles d'âge et de composition chimique entre les parties contrales et périphériques. Tandis que les parties centrales consistent en ZrSiO₄ pratiquement pur, les parties extérieures se composent de couches de ZrSiO₄ pur alternant avec des couches contenant de multiples éléments en traces. Les données obtenues sur les grains corrodés à l'acide ou soumis à une abrasion à l'air n'indiquent cependant pas de différence d'âge entre les parties centrales et périphériques. Ceci confirme la validité de l'âge obtenu (point d'intersection supérieur) comme âge d'intrusion.L'âge Rb-Sr est douteux, étant donné que le rapport initial⁸⁷Sr/⁸⁶Sr n'est que de 0,7027, valeur improbable pour un granite felsique du ProtérozoÏque supérieur. Il paraÎt raisonnable de supposer une rotation de l'isochrone, due à une migration de Rb et Sr durant un événement à basse température. Cet événement serait également responsable de l'altération des biotites et des plagioclases. Ces données fournissent un argument supplémentaire en faveur d'un magmatisme ensialique pendant la période qui suit la formation de la lithosphère.

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- U/Pb, Rb/Sr. , . — . . Western Gneiss Segments — 1552 _–36 ⁺³⁸ 1499 _–36 ⁺³⁶ (2). . , air abrasion technique. — Eastern Gneiss Segments —, 50 . U/Pb 1140 _–52 ⁺⁵⁴ Ma ( ), Rb/Sr - 1104 ± 100 ; , . . , . , : , air abrasion technique . ZrSiO₄, ZrSiO₄, . air abrasion technique . , ., Rb/Sr, , ⁸⁷Sr/⁸⁶Sr (0,7027), . . - . — , , , . , .

     

Concentration pattern during turbulent dispersion

The inertial subrange of the atmospheric turbulence spectrum extends downward from some 25 m in linear size. Energy is supplied to large eddies and cascades down the size range. The physics implies a certain concentration pattern for material being dispersed. The concentration frequency distribution (for very many ‘equal’ samples) should be log-normal with invariant slope, independent even of sample size. Correlations should be invariant if time lag or distance is measured in units proportional to linear sample size. Even sources with different characteristics might produce similar features. Turbulent dispersion data with air ions as tracer provide a means for testing the theory. Digitized and statistically processed data from 4 instantaneous-source and 8 continuous-source experiments agree well with the theory. Two other experiments, where analog data only are available, also support the conclusions.     

Reservoir characterization of the Cardium Formation, Pembina Field in Alberta

<正>The late Cretaceous Cardium Formation,which existing in the mud shale Colorado Group has the highest hydrocarbon volumes in the Western Canada Sedimentary Basin(WCSB)of Alberta.It represents approximately 20percent of the hydrocarbons indentified in WCSB as initial volume-in-place and as remaining established reserves.The Cardium Formation is developed from the very     

A discussion of structural and thermal control of magnetic anomalies on the mid-Norwegian margin

We discuss the correlation between the depth extent of magnetic sources, the Curie temperature depth and crustal structures on the mid-Norwegian margin. Spectral methods can be used to estimate the depth extent of magnetic sources, even if the bottom is located in the lower crust, however, only with limited resolution. The bottom of the magnetic surfaces is often regarded to represent the depth to the Curie isotherm. However, comparison with a 3D model based on the interpretation of potential field and seismic reflection data and thermal modelling shows that the depth extent of the magnetic sources is merely controlled by the overall geometry of the crystalline crust and not the temperature distribution. The observed changes in the magnetic field between the inner and outer part of the mid-Norwegian margin appears not to reflect, as previously assumed, the depth to the Curie temperature but the geometry of the basement and lower crust. Our 3D model of the mid-Norwegian margin reveals a basement configuration that involves a basement with different petrophysical properties, which can be connected with lithological basement units of onshore Norway.     

Diatom stratigraphy in five offshore sediment cores from the northwestern Baltic proper implying large scale circulation changes during the last 8500 years

Five Holocene sediment cores from the northwestern Baltic proper were analysed for lithology, siliceous microfossil assemblages and geochemical parameters. The data indicate that surface water salinity and redox conditions below the halocline have changed drastically at least four times since the Baltic Sea changed from a fresh water lake (the Ancylus Lake) to a semi-enclosed brackish water sea (the Litorina Sea) c. 8500 yrs BP. These variations appear to be mainly effects of changes in water depth at the thresholds of inlet areas. Based on these changes, and earlier studies of the shoreline displacement in the inlet areas, we propose a tentative model for changes of large scale water circulation in the Baltic Sea during the last c. 8500 yrs.At the transition from fresh to brackish water 8500 ¹⁴C yrs BP, upwelling of nutrient rich bottom water started to occur, causing a slight increase in primary production. Diatom assemblages in sediments indicate a slow rise in surface water salinity during this period.At 7000-6500 ¹⁴C yrs BP, surface water salinity and primary production simultaneously increased, as anoxic bottom conditions were established at depth below the halocline. We suggest that high primary production was caused by increased input of oceanic water, leading to increased upwelling of nutrient rich bottom water. At the anoxic bottoms laminated sediments formed until 5000-4500 ¹⁴C yrs BP. This period (c. 7000-4500 ¹⁴C BP) was contemporaneous with the post-glacial transgression maximum in Öresund, and we suggest it represents the most saline phase of the Baltic Sea post-glacial history.Due to a regression in Öresund starting 4500 ¹⁴C yrs BP, upwelling decreased and the halocline was lowered, resulting in decreased primary productivity and hence oxic deep water conditions. The diatom assemblages of the sediments indicate a lowering of salinity at the beginning of this period.We suggest that the second period of anoxic bottom conditions c. 2000-1500 ¹⁴C yrs BP was caused by a change of dominating inflows from the Öresund to the Belt Sea. This resulted in decreased salinity of the inflowing water which did not penetrate to the deepest parts of the basin as frequently as before. The diatom record indicates both a second lowering of salinity and a change in the large scale water circulation at the beginning of this period.     

Evolving neural network using variable string genetic algorithm for color infrared aerial image classification

Coastal wetlands are characterized by complex patterns both in their geomorphlc and ecological teatures. Besides field observations, it is necessary to analyze the land cover of wetlands through the color infrared （CIR） aerial photography or remote sensing image. In this paper, we designed an evolving neural network classifier using variable string genetic algorithm （VGA） for the land cover classification of CIR aerial image. With the VGA, the classifier that we designed is able to evolve automatically the appropriate number of hidden nodes for modeling the neural network topology optimally and to find a near-optimal set of connection weights globally. Then, with backpropagation algorithm （BP）, it can find the best connection weights. The VGA-BP classifier, which is derived from hybrid algorithms mentioned above, is demonstrated on CIR images classification effectively. Compared with standard classifiers, such as Bayes maximum-likelihood classifier, VGA classifier and BP-MLP （multi-layer perception） classifier, it has shown that the VGA-BP classifier can have better performance on highly resolution land cover classification.     

Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices

NGC 1316 is a giant, elliptical galaxy containing a complex network of dark, dust features. The morphology of these features has been examined in some detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is found that most of the features are constituted of long filaments. There also exist a great number of dark structures protruding inwards from the filaments. Many of these structures are strikingly similar to elephant trunks in H ii regions in the Milky Way Galaxy, although much larger. The structures, termed mammoth trunks, generally are filamentary and often have shapes resembling the letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved into two or more filaments, many of which showing signs of being intertwined. A model of the mammoth trunks, related to a recent theory of elephant trunks, is proposed. Based on magnetized filaments, the model is capable of giving an account of the various shapes of the mammoth trunks observed, including the twined structures.