FIRE 2 Geographic constraints

The FIRE 2 profile is 216 km long and it runs in a generally north to south direction across the southern part of the Central Finland granitoid complex (CFGC), the arc complex of western Finland, and the northern part of the arc complex of southern Finland. In its southernmost (CMP 7463–8999) part the profile turns into a northeast–southwest direction.

FIRE 2 Geological and tectonic division

The upper crust along the FIRE 2 profile has been divided into four parts: The Keitele (1), Tampere (2), Pirkanmaa (3), and Häme (4) domains.

Geological description of the Häme domain (FIRE 2 CMP 6860–8999)

The Häme domain (CMP 6860–8999) corresponds to the Häme belt, which represents relatively juvenile island arc -type supracrustal material that was squeezed between two 2.1–2.0 Ga microcontinental blocks (Bergslagen and Keitele) around 1.84 Ga.

The Häme belt (Kähkönen, 2005) belongs to the southern Svecofennian sub-province (e.g., Lahtinen et al., 2016) or the Arc complex of Southern Finland (Korsman, 1997). Bulk of the Häme belt comprises metasedimentary and metavolcanic units with a relatively juvenile geochemical affinity (Kähkönen, 2005; Lahtinen et al., 2005).

Towards the south, the metasediments have been strongly migmatized by the 1.84–1.81 Ga, peraluminous, S-type lateorogenic granites (cf., Nironen, 2005; Kukkonen and Lauri, 2009; Kurhila et al., 2010). The granites were generated by partial melting and migmatization of the same metasedimentary rocks they are intruding, which possibly happened in response to extensional collapse during the final stages of the Svecofennian orogenic evolution (Kurhila, 2011).

FIRE 2 References

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.

Huhma, H., 1986. Sm–Nd, U–Pb and Pb–Pb isotopic evidence for the origin of the Early Proterozoic Svecokarelian crust in Finland. Bulletin of the Geological Survey of Finland 337, 48 p.

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

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.

Kukkonen, I.T. & Lauri, L.S., 2009. Modelling the thermal evolution of a collisional Precambrian orogeny: high heat production migmatitic granites of southern Finland. Precambrian Research 168, 233-246.

Kurhila, M., Vaasjoki, M., Mänttäri, I., Rämö, T., & Nironen, M. 2005. U-Pb ages and Nd isotope characteristics of the Lateorogenic, migmatizing microcline granites in southwestern Finland. Bulletin of the Geological Society of Finland 77, 105–128.

Kurhila, M., Andersen, T., Rämö, O.T., 2010. Diverse sources of crustal granitic magma: Lu-Hf data on zircon in three Paleoproterozoic leucogranites of southern Finland. Lithos, 263-271.

Lahtinen, R., Korja, A. & Nironen, M., 2005. Paleoproterozoic tectonic evolution. In: Lehtinen, M., Nurmi, P.A., Rämö, O.T. (eds). Precambrian Geology of Finland – Key to the Evolution of the Fennoscandian Shield. Developments in Precambrian Geology, Volume 14. Elsevier, Amsterdam, 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.

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.

Nironen, M., Korja A., Heikkinen P. and the FIRE Working Group, 2006. A geological interpretation of the upper crust along FIRE 2 and FIRE 2A. Geological Survey of Finland, Special Paper 43, 77–103.

Suominen, V., 1991. The chronostratigraphy of southwestern Finland, with special reference to Postjotnian and Subjotnian diabases. Bulletin of the Geological Survey of Finland 356, 100 p.