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Abstract

The 187 km long line 4N was recorded in 1985 as part of the DEKORP project, the German continental seismic reflection program, and served as a basis for a network of six seismic reflection lines KTB 8501 – 8506, which were performed to investigate the planned target area for the Continental Deep Drilling Program (KTB) in the Upper Palatinate. The aim of the survey 4N was to explore the crustal structure of the central Mid-European Variscides down to the Moho and the uppermost mantle with high-fold near-vertical incidence vibroseis acquisition and, in particular, to scan the suture between the Moldanubian Zone and the northward adjacent Saxothuringian Zone. Details of the experiment, first results and interpretations were published by DEKORP Research Group (1987, 1988). The Technical Report of line 4N gives complete information about acquisition and processing parameters. The European Variscides, extending from the French Central Massif to the East European Platform, originated during the collision between Gondwana and Baltica in the Late Palaeozoic. Due to involvement of various crustal blocks in the orogenesis, the mountain belt is subdivided into distinct zones. The external fold-and-thrust belts of the Rhenohercynian and Saxothuringian as well as the predominantly crystalline body of the Moldanubian dominate the central European segment of the Variscides. Polyphase tectonic deformation, magmatism and metamorphic processes led to a complex interlinking between the units. The Saxothuringian represents the infill of a Cambro-Ordovician basin. The Moldanubian contains blocks of pre-Variscan crust and their Palaezoic cover. During the Variscan orogeny the Moldanubian crust was thrust towards the NW over the Saxothuringian foreland. Both units were welded together by a low-pressure metamorphism accompanied by polyphase deformation (DEKORP Research Group, 1987, 1988). The SE-NW striking line 4N runs along the western border of the Bohemian Massif perpendicular to the main tectonic trend (SW-NE). The profile starts in the Bavarian Forest and runs across the Upper Palatinate Forest. Shortly before the NE-trending Erbendorf Line, which separates the Moldanubian unit from the Saxothuringian unit, the profile runs through the area of the KTB drill site. In the Saxothuringian DEKORP 4N runs through the Fichtel Mountains, the Muenchberg Gneiss Complex and ends in the Franconian Forest. In the Bavarian Forest the line 4N traverses DEKORP 4Q nearly perpendicularly. Farther northwest the profile crosses KTB 8501 – 8503, which were arranged parallel to strike of the orogenic belt, as well as the DEKORP 3-D survey ISO 1989 around the KTB drill hole. In the Muenchberg Gneiss Complex the 4N profile is intersected by DEKORP 3B/MVE (East), which runs along the southern margin of the Saxothuringian belt in a SW-NE direction.