Collision tectonics involving juvenile crust: The example of the southern Finnish Svecofennides

This paper presents a reappraisal of the main structural and metamorphic features of the Southern Svecofennian Arc Complex (southern Finland) and provides new data that allow us to reconsider its tectonic evolution. Results emphasize that (1) regional shortening was accommodated by distributed thickening with no clear evidence for large-scale thrusting, (2) syn-convergence lateral flow of ductile crust most probably competed with crustal thickening since early stages of deformation, (3) no evidence exists for thickening-driven extensional collapse associated with normal shear zones, the latest structures developed being compressive, (4) exhumation appears basically driven by distributed erosion that competed with crustal thickening. Observations are interpreted in terms of a peculiar mechanical behaviour of a hot and weak juvenile lithosphere undergoing compression.