FIRE 3A Geographic constraints
The FIRE 3A profile runs for 448 km from east in the Outokumpu domain towards west over the eastern part of the Central Finland granitoid complex (CFGC) to the Äänekoski region, where it takes a turn towards northwest and crosses over the rest of the CFGC and terminates in the northwest nearby the town of Kokkola in the Bothnian Belt.
FIRE 3A Geological and tectonic division
The upper crust along the FIRE 3A profile is divided into four regions: Outokumpu (1), Savo (2), Keitele (3), and Bothnian (4) domains.
Geological description of the Savo domain (FIRE 3A CMP 3800–6000)
The Savo domain (CMP 3800–6000) corresponds to the early Paleoproterozoic Savo belt (Kähkönen, 2005), which along FIRE 3A profile consists mostly of gneisses and migmatites with supracrustal origins and juxtaposed between the slightly older upper Kaleva metasediments in the east (Viinijärvi suite; Sorjonen-Ward, 2006) and the Proterozoic Central Finland Granitoid complex in the west (Mikkola et al., 2016). The belt also coincides with the lithosphere-scale Raahe-Ladoga shear zone (RLSZ), which has been interpreted to represent the deep suture between the Archean Karelian province and the Proterozoic Svecofennian domain (e.g., Sorjonen-Ward, 2006).
Along the FIRE 3A the Savo migmatites belong to the Suonenjoki suite paragneisses with some local enrichment in more volcanic source materials and they are intercalated with the rocks of the Sorsakoski granitoid suite (Mikkola et al., 2016). The western contact of the Savo domain towards the Central Finland granitoid complex (Keitele domain) is delineated by the Iisvesi mylonite zone (Mikkola et al., 2016), which also marks the western extent of the RLSZ. Archean crust of the Kuopio complex (Hölttä et al., 2012) is inferred to underlie the entire Savo domain but it is exposed only on the northern flank of the FIRE 3A profile in the central part of the domain.
FIRE 3A References
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Elliott, B.A. 2003. Petrogenesis of the Post-kinematic Magmatism of the Central Finland Granitoid Complex II; Sources and Magmatic Evolution. Journal of Petrology 44, 1681–1701.
Kähkönen, Y., 2005. Svecofennian supracrustal rocks. In: Lehtinen, M., Nurmi, P.A., and Rämö, O.T. eds. Precambrian Geology of Finland – Key to the Evolution of the Fennoscandian Shield. Developments in Precambrian Geology 14, 343–406
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Korja, A. and Heikkinen, P.J., 2008. Seismic images of Paleoproterozoic microplateboundaries in the Fennoscandian shield. Geological Society of America, Special Paper 440, 229–248.
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Nikkilä, K., Korja, A., Koyi, H., and Eklund, O., 2015. Analog modeling of one-way gravitational spreading of hot orogens – A case study from the Svecofennian orogeny, Fennoscandian Shield. Precambrian Research 268, 135–152.
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Sorjonen-Ward, P., 2006. Geological and structural framework and preliminary interpretation of the FIRE 3 and FIRE 3A reflection seismic profiles. In: Kukkonen, I. and Lahtinen, R., eds. Finnish Reflection Experiment 2001–2005, Geological Survey of Finland Special Paper 43, 105–159.
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