Abstract
The crustal basement of Northwest Germany can be interpreted as an “Avalonian Terrane Assemblage” subdivided by a roughly NW-SE (Hercynian) and SW-NE (Rhenish) running horst and graben system. In Late Devonian and Early Carboniferous times, this assemblage was flooded by the sea and mainly marine carbonates were deposited on the horsts and Stillwater shales in the grabens, as interpretable through magnetotelluric measurements. During the Late Carboniferous Variscan Orogeny, this terrain became the coal-rich foreland of the colliding Rhenohercynian belt. The shale-filled grabens reacted through folding and thrusting with different anticlinal patterns, the main carbonate covered horst in a still unknown way. This horst was the location of the Late Carboniferous basin center and of the inverted oil-rich Mesozoic Lower Saxony Basin (southwestern sector), respectively, with the so-called Bramsche Massif therein. It probably acted as an indenter for the evolution of the Variscan ore-rich Harz Mountains and forced the approaching Rhenohercynian orogen to stack the appropriate tectonic nappes by horizontal shortening to very high altitudes and the root into large depths. Based on seismic evidence this root is still an uncompleted crust/mantle transition zone with a deep reflection seismic and petrological Moho and a shallower hardly reflecting refraction seismic velocity Moho. The alternative, partly unsolved location of the Variscan Deformation Front in Northwest Germany may represent the new findings. The results may be supported by a comparison with features of the northern Alpine deformation belt.
Highlights
Plate tectonics relates the subsurface of the Central European Basin System, which encompasses, among others, the Variscan Foreland Basin, the North German Basin as central part of the Southern Permian Basin, the inverted Lower Saxony Basin and the North Sea Basin as significant members therein (Figure 1) with the ancient pre-Devonian continent figuration of Africa (Gondwana), Baltica, Avalonia and North America (Laurentia) in a very complex manner [1] (Figure 2)
The shale-filled grabens reacted through folding and thrusting with different anticlinal patterns, the main carbonate covered horst in a still unknown way. This horst was the location of the Late Carboniferous basin center and of the inverted oil-rich Mesozoic Lower Saxony Basin, respectively, with the so-called Bramsche Massif therein
This paper briefly describes the plate tectonic history of Eastern Avalonia, its (Devonian to) Lower Carboniferous sedimentary cover by applying the magnetotelluric method as an eye-opener [13] that includes the investigation of the Bramsche anomaly as a dominant feature within the southwestern sector of the inverted Lower Saxony Basin as well, the Variscan Deformation of the Upper Carboniferous subvariscan basin fill by applying 3D-seismic [14] and how the development of the Harz Mountains and its root [15] [16] may be related to the evolution of the shape of the Variscan Deformation Front
Summary
Plate tectonics relates the subsurface of the Central European Basin System, which encompasses, among others, the Variscan Foreland Basin, the North German Basin as central part of the Southern Permian Basin, the inverted Lower Saxony Basin and the North Sea Basin as significant members therein (Figure 1) with the ancient pre-Devonian continent figuration of Africa (Gondwana), Baltica, Avalonia and North America (Laurentia) in a very complex manner [1] (Figure 2). Collisions between those plates resulted in Caledonian orogeny with the development of mountain ranges at its present-day northeastern and northwestern edges. Comparing Variscan features with Alpine ones may support the conclusions of this paper
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