prior to the svecobaltic orogeny proper there was period of northward-directed subduction at what is now south-central sweden and southern finland. the subduction lasted from 1860 to 1840 million years ago and was accompanied by magmatic activity. two trends in the southern svecofennian orogen variously overlapped in time and space: extension (1870 to 1840 million years ago) and continent-continent collision (1870 to 1790 million years ago). magmatic activity and metamorphism in southern finland ended gradually after 1870 million years ago. the orogen at southern finland with its presumed mountains and thick continental crust collapsed under the influence of gravity and spread out. by 1850 million years ago this collapse had evolved to a dynamic of extensional tectonics. in this extensional milieu short-lived sedimentary basins formed. the svecobaltic orogeny developed when subduction bought the fennoscandian craton into an oblique collision with the sarmatian craton. the mentioned sedimentary basins were destroyed by basin inversion 1830 million years ago. this last event of basin inversion was associated with a period of metamorphism in southern finland that peaked about 1820 million years ago.