Algoman orogeny geophysical measurements on the greenstone belts in Canada, suggest the metavolcanic and metasedimentary rocks of the belts project downward at least a few kilometers. The action of metamorphism on the border between granite and gneiss bodies produces a succession of metamorphosed volcanic and sedimentary rocks called greenstone belts. Most Archean volcanic rocks are concentrated within greenstone belts; the green color comes from minerals, such as chlorite, epidote and actinolite that formed during metamorphism. After metamorphism occurred, these rocks were folded and faulted into a system of mountains by the Algoman orogeny. The volcanic beds are thick. About the greenstone belt
Svecofennian orogeny broad terms, regardless of details, it has been proposed that the Svecofennian orogeny involved more-less continuous subduction with subduction zones progressively migrating to the southwest. An alternative model postulates subduction included alternating extension and compression cycles, with the orogenic activity ceasing after the collision between the Fennoscandian Craton and the Sarmatian Craton. 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