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Abstract

The 56 km long KTB Line 3 was recorded in 1985 as part of deep seismic reflection investigations for the DEKORP (German Continental Seismic Reflection Program) and KTB (German Continental Deep Drilling Program) projects. The network of lines consists of two DEKORP profiles, DEKORP 4N and its appendix 4Q, and six shorter KTB profiles, KTB 8501 – 8506, arranged in the form of a grid parallel and perpendicular to the main tectonic lineaments. The purpose of the investigations was to explore the planned target area for the Continental Deep Drilling Site in the Upper Palatinate with high-fold near-vertical incidence vibroseis acquisition. The main focus was on the crustal structure of the central Mid-European Variscides down to the Moho and the uppermost mantle and, in particular, on the suture between the Moldanubian Zone and the northward adjacent Saxothuringian Zone as well as on the metamorphic Zone of Erbendorf-Vohenstrauss. The array of the KTB profiles represents the pre-cursor of the 3-D seismic survey ISO 1989 (Integrated Seismics Oberpfalz). Details of the experiment, first results and interpretations were published by DEKORP Research Group (1987, 1988). Results discussed together with the drilling site were presented in a number of works which can be found in Emmermann & Wohlenberg (1989). The Technical Report of KTB 8503 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 toward the northwest over the Saxothuringian foreland. Both units were welded to one another by a low-pressure metamorphism accompanied by polyphase deformation (DEKORP Research Group, 1987, 1988). The WSW – ENE striking line KTB 8503 is located normally to the KTB lines 8504, 8505 and 8506 and to DEKORP 4N running ca. 16 km south of the KTB drill hole. As well as the lines KTB 8501 and 8502 the profile 8503 was arranged parallel to strike running across the NW-SE directed system of block-faults at the southwestern margin of the Bohemian Massif (DEKORP Research Group, 1988). In the southwest KTB 8503 crosses the Franconian Line, a fault zone which separates the crystalline Bohemian Massif from a foreland. Farther to the northeast KTB 8503 runs through metamorphic nappes and Variscan granites of the Erbendorf-Vohenstrauss-Zone.