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 Keitele domain (FIRE 3A CMP 6000–14800)

The Keitele domain (CMP 6000–14800) corresponds roughly to the area of the Central Finland granitoid complex (CFGC) that comprises a variety of orogenic, dominantly I-type granitic rocks and minor associated supracrustal rocks with a relatively evolved geochemical character (Nironen, 2005).

Majority of the CFGC consists of 1.89 to 1.87 Ga calc-alkaline granodiorites and granites synkinematic with the major orogenic stage corresponding to the collision of the Southern Finland arc complex (Bergslagen microcontinent and the Häme belt of the southern Svecofennia sub-province; Lahtinen et al., 2016) with the Arc complex of Western Finland (Keitele and parts of the presumed Bothnian microcontinents or the central Svecofennia sub-province; Lahtinen et al., 2016) at ca. 1.9 Ga. The 1.88 to 1.86 Ga postkinematic granitic rocks with more alkaline geochemical character (Nironen, 2005) form smaller, often discordant, intrusions with transitional I- to A-type characteristics and can be divided into three geochemical types (types 1, 2, and 3; e.g., Elliott, 2003 and references therein).

Based on the more juvenile isotopic character of the granitic rocks and the presence of larger amount of mafic rocks Lahtinen et al. (2016) also defined a separate boundary zone on the northwestern flank of the CFGC between the Bothnian domain and bulk of the CFGC.

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

Kohonen, J., 1995. From continental rifling to collisional crustal shortening – Paleoproterozoic Kaleva metasediments of the Höytiäinen area in North Karelia, Finland. Bulletin of the Geological Survey of Finland 380, 79 p.

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.

Korsman, K., Koistinen, T., Kohonen, J., Wennerström, M., Ekdahl, E., Honkamo, M., Idman, H., Pekkala, Y., (comp.) 1997. Bedrock Map of Finland, 1: 1 000 000. Geological Survey of Finland.

Kotilainen, A.K., Mänttäri, I., Kurhila, M., Hölttä, P., and Rämö, O.T., 2016a. Evolution of a Palaeoproterozoic giant magmatic dome in the Finnish Svecofennian; New insights from U-Pb geochronology. Precambrian Research 272, 39–56.

Kotilainen, A.K., Mänttäri, I., Kurhila, M., Hölttä, P., and Rämö, O.T. 2016b. New monazite U-Pb age constraints on the evolution of the Paleoproterozoic Vaasa granitoid batholith, western Finland. Bulletin of the Geological Society of Finland 88, 5-20.

Lahtinen, R., Korja, A., and Nironen, M., 2005. Paleoproterozoic tectonic evolution. 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, 481–531.

Lahtinen, R., Huhma, H., Lahaye, Y., Lode, S., Heinonen, S., Sayab, M., and Whitehouse, M.J., 2016. Paleoproterozoic magmatism across the Archean-Proterozoic boundary in central Fennoscandia: Geochronology, geochemistry and isotopic data (Sm-Nd, Lu-Hf, O). Lithos 262, 507–525.

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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.

Nikkilä, K., Mänttäri, I., Nironen, M., Eklund, O., and Korja, A., 2016. Three stages to form a large batholith after terrane accretion – An example from the Svecofennian orogen. Precambrian Research 281, 618–638.

Nironen, M., 2005. Proterozoic orogenic granitic 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, 443–479.

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.

Suikkanen, E., Huhma, H., Kurhila, M., and Lahaye, Y., 2014. The age and origin of the Vaasa migmatite complex revisited. Bulletin of the Geological Society of Finland 86, 41–55.

Williams, I.S., Rutland, R.W.R., and Kousa, J., 2008. A regional 1. 92 Ga tectonothermal episode in Ostrobothnia, Finland: implications for models of Svecofennian accretion. Precambrian Research, 165, 15–36.