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History of geological studies of the Nattanen-type granites in Finland

The geological studies on the Nattanen-type granites have a long history. In the 1920’s, during his pioneering mapping work in Finnish Lapland, Erkki Mikkola recognized for the first time these granites as young, crosscutting and petrographically typical granite intrusions (Mikkola, 1928, 1941).

The age of the Nattanen-type plutons (the Nattanen stock, the Tepasto and Pomovaara complexes, the Riestovaara and Vainospää batholiths and Juvoaivi stock on the Russian side) are dated at ~1.77–1.80 Ga. In the 1960’s, a comprehensive isotope study of rocks in Finnish Lapland, including the Nattanen-type granites, was started under supervision of Dr. Olavi Kouvo at the Isotope Laboratory for Isotope Geology, Geological Survey of Finland (GTK), Espoo. Unfortunately, only part of the isotope results was published at the time. Published Hf and Nd isotope studies (Patchett et al., 1981; Huhma, 1986) implied to major Archean crustal source component in the Nattanen-type granites.

In 1983, a new research project on the Nattanen-type granites and genetically related porphyric dykes was started by Professor Ilmari Haapala at the Department of Geology of the University of Helsinki. The aim of the project was to resolve the origin, evolution and the ore potential of the Nattanen-type granites and related rocks by geochemical, petrological and isotopic methods.  The main results of the study are published in Haapala et al. (1987), Luukkonen et al. (1989), and several M.Sc. theses.

For Eurogranites Arctic 2009, we have elaborated whole-rock geochemical data in order to enhance the typological significance and classification of the Nattanen-type granites. We have also published, in cooperation with the Laboratory for Isotope Geology at GTK,  previously unpublished U–Pb data on zircon, monazite and titanite, as well as Pb–Pb data on whole rocks and K-feldspars (Heilimo et al., submitted) to give you comprehensive view of the Nattanen-type granites.

References:

  • Front, K., Vaarma, M., Rantala, E., Luukkonen, A., 1989. Keski-Lapin varhaisproterotsooiset Nattas-tyypin graniittikompleksit, niiden kivilajit, geokemia ja mineralisaatiot. Summary: Early Proterozoic Nattanen-type granite complexes in central Finnish Lapland: rock types, geochemistry and mineralization. Geological Survey of Finland, Report of Investigation 85, Espoo, 77 p. (in Finnish with English summary).
  • Haapala, I., Front, K., Rantala, E., Vaarma, M., 1987. Petrology of Nattanen-type granite complexes, northern Finland. Precambrian Research 35, 225–240.
  • Heilimo, E., Halla, J., Lauri, L., Rämö, O.T., Huhma, H., Kurhila, M. ,Front, K. The Paleoproterozoic Nattanen-type granites in northern Finland and vicinity – a postcollisional oxidized A-type suite.  Bulletin of the Geological Society of Finland. In review.
  • 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 Geological Survey Finland 337, 48 pp.
  • Mikkola, E., 1928. Über den Nattanengranit im finnischen Lapplande. Fennia 50 (12), 22 p. (in German)
  • Mikkola, E., 1941. kivilajikartanselitys Muonio-Sodankylä-Tunsajoki. Suomen geologinen yleiskartta 1:400 000 : kallioperäkarttojen selitys lehdet B7-C7-D7. Summary: The General geological map of Finland. Helsinki: Suomen geologinen toimikunta. 286 p. (in Finnish with English summary)
  • Patchett, J., Kouvo, O., Hedge, C., Tatsumoto, M., 1981. Evolution of continental crust and mantle heterogeneity: evidence from Hf isotopes. Contributions to Mineralogy and Petrology. 78, 279–297.