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 Bothnian domain (FIRE 3A CMP 14800–17800)

The Bothnian domain (CMP 14800–17800) comprises two Paleoproterozoic metasedimentary suites of the Bothnian belt that is a part of the Arc complex of Western Finland, the Lappfors suite (Williams et al., 2008) in the west and the Pirttikylä suite, in contact with the Central Finland granite complex (CFGC), in the east (Suikkanen et al., 2014; Kotilainen et al., 2016a, 2016b).

The supracrustal rocks rim the migmatitic granitoid rocks of the Vaasa migmatite complex, the bulk of which is located west of the FIRE 3A profile (Chopin et al., 2012; Suikkanen et al., 2014; Kotilainen et al., 2016a, 2016b). The Vaasa migmatites are interpreted to represent the center of an exhumed mid-crustal metamorphic core complex generated by partial melting of the metasedimentary rocks of the Bothnian belt at ca. 1.88–1.87 Ga (Suikkanen et al., 2014; Kotilainen et al., 2016a).

Upper to mid-crustal reflectors (ca. CMP 12000–17000) that dip E–SE under the CFGC have been correlated with the contacts of the supracrustal units on the surface (Sorjonen-Ward, 2006). These reflectors extend through the present-day middle crust and are interpreted as marking the contacts of the Bothnian belt blocks with each other and “the Pirttikylä block” towards the CFGC (Sorjonen-Ward, 2006). Tectonic interpretations of these reflectors suggest them to be either thrust-related (Sorjonen-Ward, 2006) or reactivated extensional (Nikkilä et al., 2015) features.

FIRE 3A References

Chopin, F., Korja, A., Hölttä, P., 2012. Tectonometamorphic evolution of the Bothnian belt within the Svecofennian orogen – a case study for the building of a large dome in the Paleoproterozoic. LITHOSPHERE 2012 Symposium, November 6-8, 2012, Espoo, Finland, Abstracts, pp. 5–8.

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.

Mikkola, P., Lukkarinen, H., Luukas, J. 2016. Suonenjoen kartta-alueen 3241 kallioperä ja kivilajiyksiköt. Geological Survey of Finland, Archive Report, 29/2016, 30 p.

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.