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Annakaisa Korja University of Helsinki

Accretionary growth of Paleoproterozoic Fennoscandia: results from deep seismic experiments BABEL, FIRE and SVEKALAPKO. Annakaisa Korja University of Helsinki ---------------------------------------------------------------- Penrose Conference 18 th June 2006. Conclusions.

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Annakaisa Korja University of Helsinki

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  1. Accretionary growth of Paleoproterozoic Fennoscandia: results from deep seismic experiments BABEL, FIRE and SVEKALAPKO Annakaisa Korja University of Helsinki ---------------------------------------------------------------- Penrose Conference 18 th June 2006

  2. Conclusions • Modern plate tectonic settings – subduction zone, collision zone, continental extension and transform boundaries – are identified within the Paleoproterozoic Svecofennian Orogen. • The Svecofennian is composed of accreted Paleoproterozoic terranes and intervening basins. • The crust was thickened via stacking during accretionary orogen. • The thicken crust was stabilized via gravitational collapse and associated mafic underplating. • Modern Wilson cycle began to operate only after the accretionary Svecofennian Orogeny <1.8 Ga.

  3. ”Svecofennian Orogen” Crustal thickness 46-65 km High velocity lower crust non-reflective Lithosphere thickness >200 km Archean 3.2 -2.5 Ga ”Svecofennian Orogen” 1.92-1.76 Ga

  4. CFGC Lahtinen et al. 2005 after Luosto 1997 Lahtinen et al. 2005 adapted after Korja T. 2002 • -Crustal thickness varies 45 -65 km • Dipping mantle reflections mark • terrane boundaries • eNd (1.9 Ga) values from I-type • granitoids indicate • somewhat older Paleoproterozoicsource (–1.6 to +0.6 ) for CFGC • younger source (+1.5 to +4.4) for the schist belts. - Dipping conductors mark closed basins.

  5. Allochthonous unit Raahe-Ladoga transform Older nucleus Margin of Archean craton subduction zone Korja and Heikkinen, 2005 BABEL 4&3 -profile SW 4A 4 3 NE

  6. 1 6 C Swedish coastal lines Line 6 Line B Line C 3 B BABEL Finnish coastal lines 4 4A Line 1 Line 4, 4A, 3 Korja and Heikkinen, 2005 BABEL collage

  7. Thick core was stabilized by the underplating Later collisions have accreted only little new crust around the core. Later new oceans have opened along the core margins: preGrenvillian, Tethys-, Atlantic Ocean. The Wilson cycle began to operate only after the big enough core had been accreted and stabilized in the Svecofennian orogeny. ”Svecofennian Orogen”

  8. References: • Korja, A. and Heikkinen,P., 2005. The accretionary Svecofennian orogen –insight from the BABEL profiles. Precambrian Res. 136, 241-268. • 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. Elsevier Science B.V., Amsterdam, pp. 481–532. • Korja, A., Korja, T., Luosto, U., Heikkinen. P., 1993. Seismic and geoelectric evidence for collisional and extensional events in the Fenno-scandian Shield – implications for Precambrian crustal evolution. Tecto-nophysics 219, 129–152. • Korja, T., Engels, M., Zhamaletdinov, A.A., Kovtun, A.A., Palshin, N.A., Smirnov, M.Yu., Tokarev, D.A., Asming,V.E., Vanyan, L.L., Vardaniants, I.L. and the BEAR Working Group, 2002. Crustal conductivity in Fennoscandia—a compilation of a database on crustal conductance in the Fenno-scandian Shield. Earth, Planets, Space 54, 535–558. • Luosto, U., 1997. Structure of the Earth’s crust in Fennoscandia as revealed from refraction and wide-angle reflection studies. In: L.J. Pesonen (Ed.), The lithosphere in Finland - a geophysical perspective. Geophysica 33, 3–16.

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