FIRE 1 Geographic constraints

The eastern part of the 500 km long FIRE 1 line runs east to west and transects the Neoarchean Lentua complex (Hölttä et al., 2012) that includes the Eastern and Western Kianta blocks separated by the Kuhmo greenstone belt (Korja et al., 2006).

Towards the west the profile crosses the Paleoproterozoic Kainuu belt and the intertwining slivers of the prominently Archean Kalpio (Kajaani), Manamansalo, and Rautavaara complexes (Hölttä et al., 2012). Further to the southwest, the profile crosses the partly Mesoarchean Iisalmi complex (Hölttä et al., 2012) and the Archean–Proterozoic boundary to the Paleoproterozoic Savo belt.

The profile continues southwestward, towards the center of the Paleoproterozoic Central Finland Granitoid Complex and terminates north of the town of Keuruu in Central Finland.

FIRE 1 Geological and tectonic division

The upper crust along the FIRE 1 profile has been divided into five parts: The Kianta (1), Kainuu (2), Iisalmi (3), Savo (4), and Keitele (5) domains.

Geological description of the Savo domain (FIRE 1 CMP 9500–11000)

The Savo domain (CMP 9500–11000) corresponds to the part of the Paleoproterozoic (ca. 1.93–1.92 Ga) Savo belt (Kähkönen, 2005) that was redefined as the older Svecofennian supracrustal group (ca. 1.92 Ga) by Lahtinen et al. (2015).

Along FIRE 1 profile the rocks of the Savo belt consist dominantly of the island-arc -type volcanic rocks of the Pyhäsalmi and Vihanti suites squeezed between the Archean Iisalmi complex (Hölttä et al., 2012; Lahtinen et al., 2015) and its Karelian metasedimentary cover (eastern Näläntöjärvi and Salahmi suites; Lahtinen et al., 2015) in the east and the Proterozoic Central Finland granitoid complex (CFGC) in the west (Kähkönen, 2005; Nironen, 2005). The Savo 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, or the A–P boundary (Lahtinen et al., 2015).

Kontinen and Paavola (2006) interpret a steep lithospheric-scale Archean-Proterozoic boundary to lie between the eastern contact of the Savo belt towards the Kalevian metasedimentary sequences, concurrent with the strike-slip model for the cratonic boundary. In contrast, Korja et al. (2006) and Lahtinen et al. (2015) suggest that Archean middle and lower crust underlie the Savo belt as well, and that the deep Archean-Proterozoic border would be located further west, closer to the surface boundary of the Central Finland granitoid complex (CFGC) and Savo belt. This interpretation suggests that the original, collisional crustal architecture of the A–P boundary zone would have been preserved (Lahtinen et al., 2015).


FIRE 1 References

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