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 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.

”Svecofennian Orogen” Crustal thickness km High velocity lower crust non-reflective Lithosphere thickness >200 km ”Svecofennian Orogen” Ga Archean Ga

-Crustal thickness varies km -Dipping mantle reflections mark terrane boundaries Lahtinen et al 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 adapted after Korja T Dipping conductors mark closed basins.

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

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

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”

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