Petrography, geochemistry, and geochronology of granitoid rocks in the Neoproterozoic-Paleozoic Lufilian–Zambezi belt, Zambia: Implications for tectonic setting and regional correlation

There are several pre-orogenic Neoproterozoic granitoid and metavolcanic rocks in the Lufilian–Zambezi belt in Zambia and Zimbabwe that are interpreted to have been emplaced in a continental-rift setting that is linked to the break-up of the Rodinia supercontinent. However, no geochemical data were previously available for these rocks in the Zambian part of the belt to support this model. We conducted petrographic and whole-rock chemical analyses of the Neoproterozoic Nchanga Granite, Lusaka Granite, Ngoma Gneiss and felsic metavolcanic rocks from the Lufilian–Zambezi belt in Zambian, in order to evaluate their chemical characteristics and tectonic settings. Other magmatic rocks of importance for understanding the evolution of the belt in Zambia, included in this study, are the Mesoproterozoic Munali Hills Granite and associated amphibolites and the Mpande Gneiss. The Neoproterozoic rocks have monzogranitic compositions, aluminum-saturation indices (ASI) < 1.1, and high contents of high field strength elements (HFSE) and rare earth elements (REE). The chondrite-normalised spider diagrams are similar to those of A-type granites from the Lachlan fold belt and show negative Sr, P, and Ti anomalies. On various tectonic discrimination diagrams the Neoproterozoic rocks plot mainly in A-type granite fields. These petrographic and trace element compositions indicate that these rocks are A-type felsic rocks, but they do not have features of granites and rhyolites emplaced in true continental-rift settings, as previously suggested. On the basis of the A-type features and independent regional geological and geochronological data, we suggest that the Neoproterozoic granitoid and felsic metavolcanic rocks were emplaced during the earliest extensional stages of continental rifting in the Lufilian–Zambezi belt. The apparent continental-arc like chemistry of the granitoid and felsic metavolcanic rocks is thus inferred to be inherited from calcalkaline sources. The Mesoproterozoic Munali Hills Granite and Mpande Gneiss have trace element features e.g., Nb–Ta depletions, which indicate that that these gneisses were emplaced in a convergent-margin setting. The MORB-normalised spider diagram of co-magmatic amphibolites exhibit a fractionated LILE/HFSE pattern recognized in subduction zones. This inference is consistent with remnants of ocean crust, juvenile Island arcs and ophiolites elsewhere in the Mesoproterozoic Irumide belt in Zambia and Zimbabwe. In addition, we report the first U–Pb zircon age of 1090.1 ± 1.3 Ma for the Munali Hills Granite. The age for the Munali Hills Granite provides new constraints on correlation and tectono-thermal activity in the Lufilian–Zambezi belt. The age of the Munali Hills Granite indicates that some supracrustal rocks in the Zambezi belt of Zambia, which were previously thought to be Neoproterozoic and correlated with the Katanga Supergroup in the Lufilian belt, are Mesoproterozoic or older. Consequently, previous regional lithostratigraphic correlations in the Lufilian–Zambezi belt would require revision.     

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Analyse von Echogrammen zur Ermittlung der wahren Profile von SanddÜnen am Boden der Nordsee

Zusammenfassung Es werden Überlegungen angestellt, in welchen Fällen es erlaubt ist, die in den Echogrammen aufgezeichneten Profile von unterseeischen SanddÜnen ohne Entzerrung auszuwerten, und in welchen Fällen das nicht erfolgen darf. Die EinflÜsse des mit der Tiefe veränderlichen Durchmessers des Wirkbereiches einer Echolot-Anlage und der Echolänge auf die echographische Aufzeichnung und Auswertung werden diskutiert. Die Berechnung des Wirkbereichsdurchmessers und die Zeichnung der Schallschwingerkennlinie ist Voraussetzung fÜr die Beurteilung der Frage der Abbildungstreue; beides wird an Hand eines praktisch gewonnenen Echogramms fÜr ein Profil durchgefÜhrt. Aus bestimmten Formen der geschriebenen Profile und den Echolängen wird geschlossen, daß den Großrippeln gelegentlich Kleinrippeln Überlagert sind. HierfÜr wird ein Echogramm aus jÜngerer Zeit als Beweismittel gezeigt und diskutiert; die Grenzen der Auflösung zur Erfassung derartiger Kleinrippeln können aus den physikalischen Daten der Echolot-Anlage und den jeweils vorliegenden Tiefenverhältnissen berechnet werden.

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Analysis of echograms made with a view to reveal the true profiles of sand dunes on the bottom of the North Sea

Summary The question is considered which cases may and which may not allow to utilize the echo records of profiles of submarine sand dunes without slope corrections. The influences are discussed the diameter of the effective range of an echo sounding equipment and the echo lengths exert on the echograms and, hence, on their evaluation, bearing in mind that the diameter of the effective range varies with the depth. If the trueness to nature of the echograms is to be judged it is indispensable to calculate the diameters of the cross-sections and to plot the characteristic of the cone; both these operations are explained with the aid of an echogram of a submarine profile. From certain forms of the recorded profiles and from the echo lengths it is concluded that small ripples are sometimes superimposed upon great ripples. An echo record of recent date which is discussed here gives evidence of this kind of superposition. The limits of resolution which may still allow to recognize this kind of small ripples can be calculated from the physical data of the echosounding equipment and from local depths conditions.

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Analyse d'échogrammes de sondeurs ultra-sonores faite pour révéler les vrais profils de dunes de sable sur le fond de la mer du Nord

Résumé On examine les circonstances dans lesquelles il est permis ou non d'exploiter les enregistrements d'écho des profils de dunes sousmarines sans corriger l'erreur de pente. On expose les influences que le diamètre du champ d'opération d'un sondeur ultra-sonore et la longueur d'écho exercent sur les enregistrements d'écho et, par conséquent, sur leur interprétation. (Il est peut-Être à propos de rappeler ici que le diamètre du champ d'opération de l'instrument varie avec la profondeur.) Si l'on veut juger jusqu'à quel degré les enregistrements d'échos s'accordent avec les profils actuels sousmarins il est indispensable de calculer le diamètre du champ d'opération et de tracer la caractéristique du cÔne des ondes sonores; l'exécution de ces deux opérations est démontrée à l'aide de l'enregistrement d'un profil sousmarin. Certaines formes des profils enregistrés et les longueurs d'écho nous permettent d'en tirer la déduction que de petites rides souvent superposent les grandes rides. Un récent graphique d'échos exposé dans ce travail fait preuve de la présence de ce type de superposition. Les limites de la résolution qui permettent encore de reconnaÎtre ces petites rides peuvent Être calculées des données physiques du sondeur ultra-sonore et des profondeurs locales.

     

New paleomagnetic results from Upper Cretaceous arc-type rocks from the northern and southern branches of the Neotethys ocean in Anatolia

International Journal of Earth Sciences - A paleomagnetic study of Cretaceous arc type rocks in the Central-Eastern Pontides and in the Southeastern Taurides investigates the tectonic and...     

Nutrient budgets for European seas: a measure of the effectiveness of nutrient reduction policies

Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic.     

Effect of enhanced water exchange on ecosystem functions in backwaters of an urban floodplain

This study evaluated the effects of a controlled surface water connectivity scheme on several backwaters in an urban floodplain within the city limits of Vienna, the Upper Lobau. A phosphorus budget and ecosystem metabolism measurements were used to assess the reaction of two trophically distinct floodplain backwater sections on changed connectivity conditions. The surface water connection led to a reduction of the retention times in the backwater system. The water column nutrient concentrations in the individual backwater sections approached those of the source water body. The significance of these effects, however, depends on the historical and current trophic situation of the respective water bodies. Generally, the surface water connectivity introduced particulate phosphorus export up to 30% increase over the influent loading and dissolved phosphorus up to 14% increase over the influent loading. However, in sections with submersed macrophyte development, which provided enhanced filtering capacities for particulate matter, sediment and phosphorus accumulation rates were increased. At the same time, water transparency increased resulting in a positive feedback supporting further macrophyte development. Based on these findings, the evaluation of restoration measures in urban floodplains needs to consider the spatial and temporal dynamics of nutrients and ecosystem processes such as gross primary production and community respiration to predict long-term development.     

Measurements of meteor smoke particles during the ECOMA-2006 campaign: 2. Results

The first sounding rocket of the European ECOMA-project (ECOMA, Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere) was launched on 8 September 2006. Measurements with a new particle detector described in the companion paper by Rapp and Strelnikova [2008. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 1. Particle detection by active photoionization. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.06.002] clearly showed meteor smoke particle (MSP) signatures in both data channels. The data channels measure particles directly impacting on the detector electrode and photoelectrons from the particles actively created using ionization by the UV-photons of a xenon-flashlamp. Measured photoelectron currents resemble model expectations of the shape of the MSP layer almost perfectly, whereas derived number densities in the altitude range 60–90 km are larger than model results by about a factor of 5. Given the large uncertainties inherent to both model and the analysis of our measurements (e.g., the composition of the particles is not known and must be assumed) we consider this a satisfactory agreement and proof that MSPs do extend throughout the entire mesosphere as predicted by models. The measurements of direct particle impacts revealed a confined layer of negative charge between 80 and 90 km. This limited altitude range, however, is quantitatively shown to be the consequence of the aerodynamics of the rocket flight and does not have any geophysical origin. Measured charge signatures are consistent with expectations of particle charging given our own measurements of the background ionization. Unfortunately, however, a contamination of these measurements from triboelectric charging cannot be excluded at this stage.     

Feed forward neural network and interpolation function models to predict the soil and subsurface sediments distribution in Bam,Iran

An application of the artificial neural network (ANN) approach for predicting mean grain size using electric resistivity data from Bam city is presented. A feed forward back propagation network was developed employing 45 sets of input data. The input variables in the ANN model are the electrical resistivity, water table as a Boolean value and depth; the output is the mean grain size. To demonstrate the authenticity of this approach, the network predictions are compared with those from interpolation methods and the same data. This comparison shows that the ANN approach performs better results. The predicted and observed mean grain size values were compared and show high correlation coefficients. The ANN approach maps show a high degree of correlation with well data based grain size maps and can therefore be used conservatively to better understand the influence of input parameters on sedimentological predictions.