Beschreibung
The drilling activities at the KTB location in the Oberpfalz, Bavaria, started on 22 September 1987. In 1989 the KTB pilot borehole (Vorbohrung, VB) reached a depth of 4000.1 m. The KTB main borehole (Hauptbohrung, HB) was spudded on 6 October 1990 and reached its final depth of 9101 m on 10 October 1994. The essential results of the whole project were summarized by Emmermann (1995).
The KTB drill site is located in the northern part of the Zone Erbendorf-Vohenstrauss (ZEV), approximately 3 km NW of the town of Windischeschenbach, Oberpfalz. A detailed description of the ZEV and the neighbouring units is given by Stettner (1992). The ZEV is a small NW- to SE- to NNW- to SSE-trending MP metamorphic unit. It is composed of alternating paragneisses and different types of metabasic rocks, probably of pre- or early-Ordovician protolith age (Gneiss-metabasite complex or Neustadt group).
In the north the ZEV is in contact with the metabasic and meta-ultramafic rocks of the Erbendorf greenschist zone and the metasediments and metavolcanics of the Wetzldorf unit. The latter units are separated from the dominantly low-grade metamorphic Cambrian to Lower Carboniferous rocks in the southern part of the Saxothuringian zone (Kossmat 1927) by the Erbendorf line. In the east and south, the ZEV borders on high-grade metamorphic rocks of the Moldanubicum. The imbricated boundary zone is characterized by the occurrence of relics of the Wetzldorf unit. The contacts between the above units are partially obscured by the dioritic to granitic intrusions of the Carboniferous Oberpfalz pluton (Steinwald, Falkenberg and Leuchtenberg massifs). In the SW, the basement units are thrust to the SW upon Permocarboniferous and Mesozoic sediments of the South German block. The most important thrust movements occurred along the Franconian lineament, a NW- to SE-trending crustal- scale fault system that was repeatedly active during late- and post-Variscan times. Lithologically, the north part of the ZEV can be subdivided into an upper gneiss-rich unit (Püllersreuth subgroup) in the SW and a lower unit with abundant metabasites (Windischeschenbach subgroup) in the NE (Hirschmann 1994). Both units generally dip SW.
The KTB drill site is situated in the area of the Windischeschenbach unit.
Due to technical problems during the drilling operations, the profile of the VB is composed of three sections:
- hole 1 (VB1, 0-1998.3 m),
- hole 2 (VB1a, 1709.0-3893.0 m) and
- hole 3 (VB1b, 3766.9-4000.1 m).
The VB was nearly continuously cored with the exception of four phases of directional drilling and/or sidetracking (three small intervals of the upper sections VB1 and VB1a and the whole section of VB1b). The geological investigations are mainly based on core samples (core recovery 3276 m) and subordinately cuttings and rock flour. Borehole measurements including logs for the structural investigation [Formation Micro- Scanner (FMS); BoreHole TeleViewer (BHTV)] provide continuous information of the whole profile.
Geological data recovered in the field laboratory are summarized in Röhr et al. (1990).
Borehole measurements cover the whole profile.
References
Emmermann R (1995) Abenteuer Tiefbohrung. Geowissenschaften, 13 (4) : 114-128
Hirschmann G (1994) The lithological units of the northern ZEV. KTB Rep 94-3 :63-74
Kossmat F (1927) Gliederung des varistischen Gebirgsbaues. Abh Sächs Geol Landesamt 1 : 1-39
Röhr C, Kohl J, Hacker W, Keyssner S, Müller H, Sigmund J, Stroh A, Zulauf G (1990) German Continental Deep Drilling Program (KTB): geological survey of the pilot hole "KTB Oberpfalz VB". KTB Rep 90-8 :B1-B55
Stettner G (1992) Geologie im Umfeld der Kontinentalen Tiefbohrung Oberpfalz. Bayerisches Geologisches Landesamt, München