755 research outputs found
Palaeozoic Amalgamation of Central Europe: an introduction and synthesis of new results from recent geological and geophysical investigations.
No full textThe Cambrian to mid Devonian basin development and deformation history of Eastern Avalonia, east of the Midlands Microcraton: new data and a review.
No full textA review is given of recently published and new data on Avalonia east of the Midlands Microcraton. The three megasequences from Cambrian to mid Devonian described in Wales and Welsh Borderland are also present east of the Midlands Microcraton (Brabant Massif, Condroz, Ardennes, Remscheid and Ebbe inliers, Krefeld high). The three mega-sequences are caused by a tectonic driving mechanism and are explained by three different geodynamic contexts: an earlier phase with extensional basins or rifting and rather thick sequences, when Avalonia was still attached to Gondwana; a second phase with a shelf basin with moderately thin sequences when Avalonia was a separate continent and a later phase with a shelf or foreland basin development and thick sequences. Deformation of the megasequences 1 and 2 or 1 to 3 varies between areas. In Wales and the Lake District the Acadian phase is long-lived and active from early to mid Devonian. In the Ardennes inliers a deformation is active between the late Ordovician and the Silurian (Ardennian Phase), with a similar intensity as the core of the Brabant Massif, when present erosion levels are compared. The Brabant Massif is partly deformed by the long-lived Brabantian Phase from late Silurian till early mid Devonian. Both the Ardennes inliers and the Brabant Massif are not classic orogenic belts, only slate belts where no more than the epizone is reached at present erosion levels. Areas supposedly close to the microcraton or basement are nearly undeformed (SW Brabant Massif and central Condroz). A model of anticlockwise rotation of Avalonia of about 55° from Caradoc to Emsian is proposed to explain the deposition setting of megasequence 3 and the subsequent Acadian and Brabantian deformation. Immediately after the Avalonian microcontinent touched Baltica in Caradoc times it created a short-lived subduction magmatic event from The Wash to the Brabant Massif and soon after the magmatism ended a foreland basin developed. Possibly during and after that development a long-lived and slow compressional event occurred, leading to the deformation of the Anglo-Brabant Deformation Belt. In the early Devonian, contemporaneous with the shortening of the Anglo-Brabant Deformation Belt, extension occurred in the Rheno-Hercynian Zone, possibly caused by the same slow rotation of Avalonia. More evidence emerges that Avalonia cast of the Midlands Microcraton comprises not one but probably two terranes: the remnant of the palaeocontinent Avalonia, and what is called the palaeocontinent Far Eastern Avalonia; the latter is only occasionally observed in the few deep boreholes into the Heligoland-Pomerania Deformation Belt, in southern Denmark, NE Germany and NW Poland, with scant available indirect data in between indicating only Proterozoic basement and no Caledonian deformation. For Far Eastern Avalonia a similar palaeogeographical history is postulated as Avalonia, with rifting from Gondwana in Arenig or earlier times, collision with Baltica before the mid-Ashgill and deformation between the late Ordovician and latest Silurian. The Avalonia concept might need to be expanded to an 'Avalonian Terrane Assemblage' with cratonic cores and small short-lived oceans as in the Armorican Terrane Assemblage.SCOPUS: ar.kinfo:eu-repo/semantics/publishe
Lower Palaeozoic basin development and Caledonian deformation history in and around Belgium in the framework of Eastern Avalonia
No full textT.C. Powers, '25, author of the book, "Leakage: The Bleeding of the American Economy"
No full textIncludes letters from the American Society for Testing Material about T.C. PowersBlack and WhitePeople: Powers, T.C
Palaeozoic terranes and their lithospheric boundaries within the Trans-European Suture Zone (TESZ): a review
No full textThe Trans-European Suture Zone (TESZ) is a broad and complex zone of terrane accretion separating ancient lithosphere of the Baltic Shield and East European Craton (EEC) from the younger lithosphere of western and southern Europe. There is debate about the number of terranes involved, and their origins. The most significant terrane boundaries, originally oceanic sutures, are poorly exposed, and are defined using faunal provinciality. Prominent geophysical lineaments may represent sub-terrane boundaries within composite terranes. The Avalonia Composite Terrane was amalgamated to Baltica in latest ician time. The provenance of the Malopolska and Moravo–Silesian terranes, whose Neoproterozoic basement is suspect with respect to Baltica, but with which they nonetheless share faunal affinities, is still debated. The extent of the Variscide Rhenohercynian Zone defines the southern limit of the early Palaeozoic-accreted terranes. Terranes within the Bohemian Massif exhibit HP metamorphism recording subduction-driven collision prior to incorporation in the TESZ collage, itself associated with a HP event. In Romania, the Saxothuringian Zone (and Rheic Suture) are directly juxtaposed with the EEC, and the crustal structure of the TESZ has been much modified by post-Palaeozoic tectonism. Deep seismic reflection data, where available, show that the oceanic sutures are frequently associated with inclined reflectivity zones (IRZ) in the lithospheric mantle, here inferred to mark relict subduction zones. Interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the IRZ, resulting from early orogenic lithospheric delamination at the Moho interface and/or post-orogenic ‘reordering’ processes. The mantle IRZ appear to indicate a N-directed polarity for early Palaeozoic subduction, apparently incompatible with the geological evidence, which indicates subduction of the Tornquist Sea beneath Avalonia, and a large amount of underthrusting of Avalonia by Baltica. Possible explanations for these apparently incompatible observations are evaluated
A compressional wedge model for the Lower Palaeozoic Anglo-Brabant Belt (Belgium) based on potential field data
No full textStructural field observations only allow kinematic inferences to be made for the southern extremity of the predominantly concealed Lower Palaeozoic Anglo-Brabant Belt. On the other hand potential field data (aeromagnetic and Bouguer anomaly maps), enable the field of vision to be enlarged. They not only corroborate the kinematics derived from structural field observations: they also reveal possible key players in the late Silurian to early Devonian deformation event causing the observed orogenic architecture. This integrated approach has led to a compressional wedge model for the Brabant Massif. It is also proposed that crystalline basement blocks, most probably of Precambrian age, controlled the kinematics. Finally, it is suggested that the development of rift or pull-apart basins in a transtensional intracontinental setting during the Cambrian may have been crucial in the subsequent deformation history of the Anglo-Brabant Belt.status: Publishe
Timing of the Avalonia-Baltica plate convergence as inferred from palaeogeographic and stratigraphic data of chitinozoan assemblages in west Pomerania, northern Poland.
No full textChitinozoa and Nd isotope stratigraphy of the Ordovician rocks in the Ebbe Anticline, NW Germany.
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The southern margin of the East European Craton: new results from seismic sounding and potential fields between the North Sea and Poland
No full textThe extension of eastern Avalonia from Britain through the NE German Basin into Poland is, in some sense, a virtual structure. It is covered almost everywhere by late Paleozoic and younger sediments. Evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks. During the last two decades, much geophysical and geological information has been gathered since the European Geotraverse (EGT), which was followed by the BABEL, LT-7, MONA LISA, DEKORP-Basin'96, and POLONAISE'97 deep seismic experiments. Based on seismic lines, a remarkable feature has been observed between the North Sea and Poland: North of the Elbe Line (EL), the lower crust is characterised by high velocities (6.8 - 7.0 km/s), a feature which seems to be characteristic for at least a major part of eastern Avalonia (far eastern Avalonia). In addition, the seismic lines indicate that a wedge of the East European Craton (EEC) (or Baltica) continues to the south below the southern Permian Basin (SPB)-a structure which resembles a passive continental margin. The observed pattern may either indicate an extension of the Baltic crust much farther south than earlier expected or oceanic crust of the Tornquist Sea trapped during the Caledonian collision. In either case, the data require a reinterpretation of the docking mechanism of eastern Avalonia, and the Elbe-Odra Line (EOL), as well as the Elbe Fault system, together with the Intra-Sudedic Faults, appear to be related to major changes in the deeper crustal structures separating the East European crust from the Paleozoic agglomeration of Middle European terranes
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