Early Proterozoic (c 2000-1900 Ma) crustal structure of the northeastern Baltic Shield: tectonic division and tectogenesis.

Abstract

Recent structural investigations in the Precambrian of northern Finnish Lapland and Norwegian Sørvaranger and their extrapolation into the neighbouring Kola Peninsula have stablished that the northeastern part of the Baltic Shield can be divided into several tectonic units consisting of Archaean to Early Proterozoic crust. The tectonic units are separated by Early Proterozoic, Svecokarelian linear thrust zines with clear evidence of deep-seated, high ductile strain deformation. From norteast to southwest, the units are: the Murmansk unit, the Sørvaranger unit, the Kola suture belt, the Inari unit, the Granulite belt, and the Tanaelv belt. The structural work combined with recently published petrological and geochronological results provides new evidence for the interpretation of the Secokarelian crustal structures in the northeastern part of the Baltic shield in terms of a plate tectonic model. The Kola suture belt is considered to mark the site of a continent-continent collision suture, which was formed by the closure of a former Kola ocean. The metaflysch sequence of the Granulite belt is interpreted as having been deposited in a back-arc basin to the southwest of the Kola ocean. This basin was floored by attenuated, partly oceanized continental crust (now the Tanaelv belt). As a result of the collision between the Sørvaranger and Inari units and the closure of the Kola ocean, the Granulite and Tanaelv belts were thrusted upon the southern foreland.