Transcript Accretionary growth of Paleoproterozoic Fennoscandia

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.
Archean 3.2 -2.5 Ga
”Svecofennian Orogen”
1.92-1.76 Ga
CFGC
Lahtinen et al. 2005 after Luosto 1997
eNd (1.9 Ga) values from I-type
Lahtinen et al. 2005 adapted after Korja T. 2002
-Crustal thickness varies 45 -65 km
granitoids indicate
-Dipping mantle reflections mark
-somewhat older Paleoproterozoic
terrane boundaries
source (–1.6 to +0.6 ) for CFGC
-younger source (+1.5 to +4.4) for - Dipping conductors mark closed basins.
the schist belts.
BABEL 4&3 -profile
SW
4A
4
3
Allochthonous unit
Older nucleus
subduction zone
NE
Raahe-Ladoga transform
Margin of
Archean craton
Korja and Heikkinen, 2005
BABEL
4A
BABEL collage
6
Swedish coastal lines
Line B
Line 1
4
1
C
Line 6
Line C
Finnish coastal lines
3
B
Line 4, 4A, 3
Korja and Heikkinen, 2005
Thick core was stabilized by the underplating
”Svecofennian Orogen”
 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.
 References:
 Korja, A. and Heikkinen,P., 2005. The accretionary Svecofennian orogen –insight from the
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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.