The migmatite complex of the Savonranta district of eastern Finland represents the combined effects of polyphase deformation, polymetamorphism and the emplacement of a series of dioritic, grandioritic, granitic and pegmatitic masses. The most significant feature in terms of both regional structure and control of neosome emplacement is a large wrench fault zone along which there has been a minimum of 30 km displacement. Its development was controlled by a stress system related to plate movement in the early-middle Proterozoic Svecokarelian orogenic belt.
Successive neosome development has been related to the extensive structural and metamorphic history of the amphibolite facies palaeosome mica schists which has been deduced from refolding and cross-cutting relationships. Rb–Sr whole-rock isotopic studies of a porphyritic granite, whose emplacement was controlled by the wrench fault regime, indicate an age of crystallisation of 1786 ± 80 m.y. The initial 87Sr/86Sr ratio of 0·7053 ± 01 shows the source region for the granite magma had a previous crustal history.
