prior to the onset of orogeny the archean-aged craton of what is today northeastern fennoscandia rifted creating an ocean basin, the "pre-svecofennian ocean", that then closed during the svecofennian orogeny. the closure of this basin was indebted to subduction and resulted thus both in the formation of igneous rocks and the emplacement of the jormua and outokumpu ophiolites about 1950 million years ago. in the later stages of the lapland-savo orogeny an island arc, the knaften arc, accreted to the keitele-karelia-norrbotten collage.