Geologian tutkimuskeskus, Tutkimusraportti 198 – Geological Survey of Finland, Report of Investigation 198, 2013 Pentti Hölttä (ed.) MAIN GEOLOGICAL FEATURES OF THE KUOPIO DISTRICT by Heikki Lukkarinen, Perttu Mikkola and Olli Äikäs Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland E-mail:
[email protected] INTRODUCTION Geologically the Kuopio district is part of the transition zone between the Svecofennian domain and the Archean craton known as Raahe−Ladoga zone and includes a variably preserved cover sequence (Karelian domain) overlying the Ar- chean basement rocks. The transition zone is interpreted as a geosuture charac- terised by NW−SE- and N−S-trending faults and shear zones, an extensive grav- ity minimum and high-grade metamorphic blocks (Koistinen 1981, Korsman et al. 1988). Bedrock mapping for the GTK 1:100 000 series has been undertaken in the much of the Kuopio district in recent years (Lukkarinen 2000, 2002, 2008, Pääjärvi & Äikäs 2005, Äikäs 2000), followed by ongoing revision and definition of rock units for the national stratigraphy database (FINSTRATI) and the nation- wide seamless bedrock map (Bedrock of Finland − DigiKP). ARCHEAN CRATON The Archean bedrock in the Kuopio district consists of the southernmost parts of the Iisalmi and Rautavaara complexes as well as numerous discrete gneiss domes (Kuopio, Rytky, Vehmasmäki, Paukarlahti, Kotalahti, Konnus and Saamainen) and tectonic slices to the west of the domes, making up the Kuopio Complex; these domes and slivers are surrounded by Paleoproterozoic supracrustal rocks. The Kuopio complex is bounded by the dextral Suvasvesi D3−D4 faults and shear zones in the east and the Airaksela D3−D4 fault in the west (Forss et al.