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Aspects of Pan-African tectonics
No full textA meeting convened at Heidelberg devoted two days, October 22nd and 23rd, 1998, to discuss a number of topics an the Pan-African of (northern) Africa. Proceeding from Egypt and Morocco as the regional focus of studies from our Heidelberg working group in the Frame of bilateral cooperation projects, we were glad to receive, and accept, contributions from other working groups an different aspects and areas of Pan-African tectonics. These contributions are now presented here. In addition, there are also a few texts from colleagues who were unable to come to Heidelberg. The Pan-African took place between c. 700 and 550 Ma ago and affected both pre-existing continental terranes and oceanic and magmatic arc terranes. For reviews, see, for example, Stern (1994), EI Gaby & Greiling (1988), Kröner (1984). Recently, it has been attempted to re-assemble Gondwana into its Pan-African shape, prior to the syn- and post-Pan-African breakup into the continents we see today, by Unrug (1996, 1997). From this latter work, Figure 1 is modified. It gives an overview over the actual area at about 650 Ma ago and shows the importance of the Pan-African orogeny for the formation of Gondwana and the surrounding continents. The present contributions cover three areas in Western Gondwana: Namibia, Morocco, and the Arabian-Nubian Shield. All three of them are highlighted by arrows. The contributions tackle various aspects of the Pan-African evolution and different episodes, starting with the pre-collisional evolution and ending with late- and post-tectonic events. Accordingly, we have tried to group the papers into three sections: I. Accretion- and collision-related magmatism, metamorphism and structure (8 contributions) II. Shear zones and mineralization(7 contributions) III. Post-collisional evolution and extension (9 contributions) A brief introduction to the individual papers is given at the beginning of each of the three sections. As a matter of fact, the arrangement may notalways appear as logical. However, we feel this grouping may show differences or similarities between the various studied regions. For this reason, we also included a study of pluton emplacement from California, since this example may be an analogue for a number of early- and [...
Magmatic evolution of a neoproterozoic Island-Arc : syn- to post-orogenic igneous activity in the Anti-Atlas (Morocco) : German - Moroccan cooperation in scientific research and technological development
No full textThis volume presents some of the first results of a cooperation between the Geology Department of the Chouaib Doukkali University at EI Jadida in Morocco and the Geologic-Palaeontologic Institute of the Ruprecht-Karls-University at Heidelberg in Germany. The main objectives of this cooperation are the understanding of the emplacement of magmatic bodies, related dykes, and mineralizations. In order to unravel the Pan-African tectonic evolution in the Anti-Atlas (Fig. 1), which led to the genesis of this magmatism and mineralization, detailed structural, microscopic and AMS work, is applied. In addition to the scientific and economic aims, the cooperation project intends to develop the general knowledge in economic and structural geology, in close cooperation with University institutions and mining companies. The first initiative from the Morroccan side was taken by Dr. Ali Bajja of EI Jadida. He is now Professor at the Cadi Ayyad University at Marrakech but still contributing actively to the cooperation project. This is documented very weil by his review paper on the Pan-African volcanism in the Anti-Atlas. More detailed studies concern the eastern Saghro in the eastern Anti-Atlas, where the cooperation between Drs. Ennih and Errami of EI Jadida and the working group at Heidelberg resulted in a number of artieles on the emplacement and evolution of granitoid plutons in the Imiter area, elose to the Imiter mine (Fig. 2). Applied methods range from petrography, geochemistry, mineral chemistry to structural and microstructural work and the application of magnetic methods. In particular, the anisotropy of the magnetic susceptibility (AMS) showed once again its high potential in determining and quantifying strain even in such rocks, where strain markers for conventional methods are lacking. With regard to the regional importance of the results, Figure 1 shows the general situation of the Anti-Atlas in the frame of the late Neoproterozoic orogenic belts, called Pan-African in present Africa, which built up the supercontinent of Gondwana. On the map, the Anti-Atlas appears to be at a marginal position with regard to [...
Late orogenic basin evolution, deformation and metamorphism in the Pan-African Basement, Wadi Queih, Eastern desert of Egypt
No full textThe present volume presents the latest contributions to the geoscientific cooperation project between the Egyptian Geological Survey and Mining Authority (EGSMA), Cairo, Arab Republic of Egypt, and the Geologisch-Paläontoloplsches Institut (GPI), Ruprecht-Karls-Universität, Heidelberg, Federal Republic of Germany. This International cooperation project is sponsored by the Federal Ministry for Education, Science, Research and Technlogy (BMBF), Bonn, through the International Bureau of Forschungszentrum Jülich. The overall objectives are to assess the structural and tectonic evolution, orogeny and terrane boundaries with particular emphasis on thelocation, nature and geometry of ore deposits. Ultimately, these cooperative efforts should lead to the comprehensive assessment and effective mining of economic minerals. The cooperat ion project has also turned attention to the very low-grade metamorphic rocks of the Hammamat Group and adjacent low-grade volcano-sedimentary sequences which host a number of important mineral deposits. These rock associations represent late-Pan-African molasse-type deposits and associated igneous rocks, which probably represent the late-tectonic stage of extensional collapse. Consequently, the Hammamat Group is represented by thick, coarse clastic sequences fining upwards into arkoses, sandstones, siltstones and mudstones. These rocks are usually conside red as being deposited in discrete sedimentary basins, commonly referred to as Hammamat Basins
Geology, geochemistry and structure of Gabal Muqsim area and environs, South Eastern Desert, Egypt
No full textBilateral Cooperation in Geosciences between the Arab Republic of Egypt and the Federal Republic of Germany and in particular the cooperation between the Egyptian Geological Survey and Mining Authority (EGSMA), Cairo, and the Geologisch-Palaontologisches Institut (GPI) of Ruprecht-Karls-University, Heidelberg has resulted in another important monograph to be published in the Scientific Series of the International Bureau of Forschungszentrum JOlich. In the frame of the general aim of the cooperation project to bring together the detailed regional knowledge of the Egyptian side with the general experience on tectonic and ore forming processes, and laboratory facilities of the German side the contribution by M. F. Sadek strikes a good balance between field-based studies in the Eastern Desert of Egypt and laboratory work and interpretation of results both at EGSMA, Cairo, and GPI, Heidelberg. Topically the project attemps to clarify the tectonic evolution of the Pan-African basement in the Eastern Desert of Egypt together with the formation and location of ore deposits. Therefore, M. F. Sadek and his co-workers selected an area within the reaches of Wadi Allaqy, where a number of well-known gold (e.g. Haimur, Abu Fas) and base metal deposits (e. g. Abu Swayel) are located. In fact, the Abu Fas mine lies within the area of the present monograph. The mine and the area as a whole are close to the southern boundary of Egpyt and partly within sight of the Sudan. Therefore the present study is the most southerly located contribution to the cooperation project so far. Besides clarifying the geologic-tectonic-genetic aspects of the known ore deposits, the work by M. F. Sadek focussed also on a major, late-tectonic ultramafic-mafic intrusion and its role in the general tectonic evolution. Whereas the tectonic importance of this intrusive body in the wider regional context of the Pan-African evolution has been discussed elsewhere (Greiling et al. 1994) it must be emphasized here that this layered, mainly gabbroic intrusion is of great economic potential with regad to Cr or platinum group elements. [...
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Structural geological and geochemical studies on the Panafrican Basement Rocks, Wadi Zeidun, Central Eastern Desert, Egypt
No full textThe present work is a geologieal, structural and geochemieal study on the Pan-African basement rocks in the area of Wadi Zeidun and its southern tributaries Wadi Maasar and Wadi Meesar, which cover approximately 600 km in the Central Eastern Desert of Egypt. Detailed field studies revealed that the area comprises four main petrotectonic assemblages: 1)- Island-arc assemblage; 2)- Volcanogenic metasediments; 3)- Molasse-type sediments, and 4)- Late-collision granitoids and felsites as well as minor dykes and veins. The island arc-assemblage in the study area includes low-k, calc-alkaline/ tholeitic metavolcanics and a volcaniclastic sequence intruded by Wadi Maasar arc-granitoids. The volcanogenic metasediments east and northeast of Gabal EI Shalul are composed mainly of a foliated, cleaved and bedded sequence of green metaconglomerates interbedded with grey phyllites, slates, metamudstones, metasiltstones and graded bedded metagreywackes. Thepetrochemical characters of these rocks revealed that they are comparable with the oceanic island are sandstones. The molasse-type sediments in the study area form three isolated exposures (basins). They are composed mainly of a succession ofinterbedded purple conglomerates, sandstones and siltstones of alluvial fan-braided stream deposition. The modal composition of these sandstones plot in the two fields of dissected are and recycled orogen. The late-collision granites are represented by two main plutons; El Shalul and El Hassanawia. Both are essentially pink in colour, composed mainly of quartz, perthite, plagioclase and minor biotite in addition to hornblende in El Hassanawia granite. The geochemistry of these granitesshows a calc-alkaline character of normal granite composition, being formed in an environment of compression. [...
Beskrivning till berggrundskartorna 25G Ammarnäs NV, NO, SV & SO (Description to the bedrock maps 25G Ammarnäs NV, NO, SV& SO)
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