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 Keitele domain (FIRE 2 CMP 0000–3800)

The Keitele domain (CMP 0000–3800) 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 Western Finland arc complex (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).

The southern part of the CFGC crosscut by the FIRE 2 profile comprises a diverse lithology of dioritic, granitic, and supracrustal rocks (Nironen et al., 2006). The supracrustal Hirsilä belt in the southern part of the domain is lithologically similar to the Tampere belt further south (Kähkönen, 2005).

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.