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 ”Svecofennian Orogen” 1.92-1.76 Ga Archean 3.2 -2.5 Ga

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

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

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

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.