FIRE 4A Geographic constraints

The FIRE 4A profile runs for 319 km in a southwest to northeast direction from Sirkka to Näätämö across the areas of central and northeastern Lapland (Patison et al., 2006). The profile commences in the Kittilä suite metavolcanic rocks and crosses over the older formations of the Central Lapland Greenstone Belt (Lehtonen et al., 1998) into the Lapland Granulite Belt (Meriläinen, 1976; Hörmann et al., 1980) and further into the diverse Archean and Proterozoic rocks of the Inari Area (Nironen et al., 2002).

FIRE 4A Geological and tectonic division

The upper crust along the FIRE 4A profile has been divided into three parts: Kittilä (1), Ivalo (2), and Inari (3) domains.

Geological description of the Kittilä domain (FIRE 4A CMP 9920–13000)

The Kittilä domain (CMP 9920–13000) corresponds to the Paleoproterozoic metasedimentary and -volcanic sequences of the Central Lapland greenstone belt (CLGB), which are at least partly correlated with the rocks of the Peräpohja schist belt (Lehtonen et al., 1998; Lahtinen et al., 2015 and references therein) and share a similar geological history.

The rocks of the ca. 2.0 Ga Kittilä suite (a.k.a. the Kittilä allochton) form a group of dominantly metavolcanic rocks with diverse geochemical signatures that are inferred to originate in a plume environment and, in contrast to the generally extensional tectonic regime, to have been emplaced in a convergent tectonic event on top of the rift-related supracrustal sequences (Lehtonen et al., 1998; Hanski and Huhma, 2005; Patison et al., 2006; Lahtinen et al., 2015).

The southern part of the FIRE 4A profile commences in and crosses over the metavolcanic rocks of the Kittilä suite just north of the Sirkka (Kittilä) shear zone that is interpreted to be the thrust surface of the allochtonous metavolcanic units (Patison et al., 2006). Further in the northeast, the profile crosscuts some of the autochtonous/parautochtonous units of the CLGB grouped collectively as the Vuotso complex that comprises a heterogeneous amalgamation of mostly Paleoproterozoic metasedimentary rocks deformed and metamorphosed during the overthrusting of the Lapland granulite belt over the CLGB.

FIRE 4A References

Daly, S.J., Balagansky, V.V., Timmerman, M.J., and Whitehouse, M.J., 2006. The Lapland-Kola orogeny: Palaeoproterozoic collision and accretion of the northern Fennoscandian lithosphere. Geological Society of London, Memoirs 32, 579–598.

Hanski, E. and Huhma, H., 2005. Central Lapland Greenstone belt. In: Lehtinen, M., Nurmi, P.A. & Rämö, O.T. (eds.) The Precambrian Geology of Finland − Key to the Evolution of the Fennoscandian Shield. Developments in Precambrian Geology 14, Amsterdam: Elsevier, 139–194.

Heilimo, E., Halla, J., Lauri, L.S., Rämö, O.T., Huhma, H., Kurhila, M., and Front, K., 2009. The Paleoproterozoic Nattanen-type granites in norhtern Finland and vicinity – a postcollisional oxidized A-type suite. Bulletin of the Geological Society of Finland 81, 7–38.

Hölttä, P., Väisänen, M., Väänänen, J., and Manninen, T., 2007. Paleoproterozoic metamorphism and deformation in Central Lapland, Finland. Geological Survey of Finland, Special Paper 44, 7–56.

Hörmann, P.K., Raith, M., Raase, P-. Ackermand, D., and Seifert, F., 1980. The granulite complex of Finnish Lapland: petrology and metamorphie conditions in the Ivalojoki - Inarijärvi area. Bulletin of the Geological Survey of Finland 308, 95 p.

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.

Marker, M., Henkel, H., and Lee, M.K., 1990. Combined gravity and magmentic modelling of the Tanaelv and Lapland Granulite Belts, POLAR profile, northern Baltic. In: Freeman, R., Giese, P., Mueller, St. (eds.) The European Geotraverse: Integrative studies: results from the Fifth Earth Science Study Centre, Rauischholzhausen, Germany, 26 March – 7 April, 1990. Strasbourg: European Science Foundation, 67–76.

Merilänen, K., 1976. The granulite complex and adjacent rocks in Lapland, northern Finland. Bulletin of the Geological Survey of Finland 281, 129 p.

Lahtinen, R., Huhma, H., Lahaye, Y., Jonsson, E., Manninen, T., Lauri, L.S., Bergma, S. , Hellström, F., Niiranen, T., and Nironen, M., 2015. New geochronological and Sm–Nd constraints across the Pajala shearzone of northern Fennoscandia: Reactivation of a Paleoproterozoic suture. Precambrian Research 256, 102–119.

Lehtonen, M., Airo, M-L., Eilu, P., Hanski, E., Kortelainen, V., Lanne, E., Manninen, T., Rastas, P., Räsänen, J., and Virransalo, P., 1998. Kittilän vihreäkivialueen geologia, Lapin vulkaniittiprojektin loppuraportti. Summary: The stratigraphy, petrology and geochemistry of the Kittilä greenstone area, northern Finland. A report of the Lapland Volcanite Project. Geological Survey of Finland, Report of Investigation 140, 144 p.

Nironen, M., Lahtinen, R., and Koistinen, T., 2002. Suomen geologiset aluenimet – yhtenäisempään nimikäytäntöön, Summary in english: Subdivision of Finnish bedrock – an attempt to harmonize terminology. Geologi 54, 8–14.

Patison, N. L., Korja, A., Lahtinen, R., Ojala, V. J., and the FIRE Working Group 2006. FIRE seismic reflection profiles 4, 4A and 4B: Insights into the Crustal Structure of Northern Finland from Ranua to Näätämö. Geological Survey of Finland, Special Paper 43, 161–222.

Sorjonen-Ward, P. and Luukkonen, E.J., 2005. Archean rocks. In: Lehtinen, M., Nurmi, P.A. & Rämö, O.T. (eds.) The Precambrian Geology of Finland − Key to the Evolution of the Fennoscandian Shield. Developments in Precambrian Geology 14, Amsterdam: Elsevier, 19−99.

Sorjonen-Ward, P., Nironen, M., and Luukkonen, E. 1997. Greenstone Associations in Finland. In: Maarten de Wit & Lewis Ashwal (eds.) Greenstone Belts. Clarendon Press, London, 677–698.

Tuisku, P. and Huhma, H., 2006. Evolution of migmatitic granulite complexes: Implications from Lapland Granulite Belt, part II: isotopic dating. Bulletin of the Geological Society of Finland 78, 143–175.

Tuisku, P., Mikkola, P., and Huhma, H., 2006. Evolution of migmatitic granulite complexes: implications from Lapland Granulite belt, part I: metamorphic geology. Bulletin of the Geological Society of Finland 78, 71–105.

Ward, P., Härkönen, I., Nurmi, P., and Pankka, H. S. 1989. Structural studies in the Lapland greenstone belt, northern Finland and their applications to gold mineralizations. Geological Survey of Finland, Special Paper 10, 71–78.