Structural sequence in the gneissose complex of eastern Finland as a basis for correlation in the Presvecokarelides

Abstract

Structures and mineral growths formed in seven successive deformational phases in gneisses in late Archaean times form a basis for the determination at chronological sequences from place to place in the Presvecokarelides of eastern and eastern central Finland. Refolded folds and refolded metamorphic rock fabrics, formed under particular P-T conditions and deformed under other P-T conditions, together with a variety of igneous masses whose positions structural sequences can be determined, provide such a complex framework that the likelihood of random matching is remote while the lack of expression of one parameter does not appreciably reduce the strength of the correlation. Isotopic data demonstrating corresponding events in the gneisses from different parts of the region is an additional factor for correlation. With this being associated with matching complex structural frameworks that show evidence of having been formed under the same successive stress systems, together with matching metamorphic and igneous histories, the gneisses of the Presvecokarelides of eastern and eastern central Finland are interpreted as having formed in one orogenic regime. Corresponding sets or features in the granitoid association of northern Finland indicate that the successively formed stress systems were operative over a large crustal segment, while the expression of the various structural metamorphic and igneous features and their interrelations correspond, in many respects, to those of orogens whose evolution has been related to the movement of large lithospheric plates.