FIRE 4B Geographic constraints

The FIRE 4B runs in an east–west/southeast–northwest direction for 62.5 km from the township of Sirkka in the east to the village of Muonio in the west.

FIRE 4B Geological and tectonic division

The upper crust along the FIRE 4B profile has been divided into two parts: Kittilä (1) and Muonio (2) domains.

Geological description of the Muonio domain (FIRE 4B CMP 1650–2500)

The Muonio domain (CMP 1650–2500) corresponds to the rocks of the Archean Norrbotten block on the western side of the Pajala shear zone (PSZ) (Lahtinen et al., 2015).

The rocks of the domain belong to the dominantly metasedimentary >2.2 Ga Virttiövaara formation that was intruded by the granitic and monzonitic rocks of the (1.9–1.86 Ga) Haaparanta (Haparanda) and (1.81–1.77 Ga) Kittilä suites (Väänänen and Lehtonen, 2001; Patison et al., 2006). The upper crust of the domain along FIRE 4B profile is divided into two blocks that are separated by a west-dipping unconformity that runs parallel to the inferred eastern flank of the PSZ (Patison et al., 2006).

FIRE 4B References

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Lahtinen, R., Korja, A., and Nironen, M., 2005. Proterozoic tectonic evolution. In: Lehtinen, M., Nurmi, P., and Rämö O.T., (eds.). Precambrian Geology of Finland – Key to the Evolution of the Fennsocandian Shield. Developments in Precambrian Geology 14, 481–531.

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.

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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.

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