Petrogenesis and evolution of an early Proterozoic collisional orogenic belt: The granulite belt of Lapland and the Belomorides (Fennoscandia)

Abstract

The tectonic and metamorphic pattern of the Precambrian crust exposed in the eastern Baltic Shield is characterized by two adjacent high-grade belts (Tana and Granulite belts) located between the Archean Inari-Kola craton to the east and the South Lapland-Karelia craton to the west. The Tana belt corresponded to a volcanic sequence (tholeiitic and calc-alkaline series) subsequently intruded by various plutonic rocks including the Vaskojoki anorthositic suite. The Granulite belt is interpreted as a flysch-like greywacke-shale sequence (khondalite suite) including impersistent volcanic layers later intruded by several igneous suites of both tholeiitic and calc-alkaline affinity (charnockitic complex). These two former belts constitute the axial part of the Belomorides, an early Proterozoic fold belt. Major parts of this mobile belt surrounding the axial zone are composed of intensely reworked Archean material. The Jatulian volcano-sedimentary formations cover large areas on both sides of the mobile belt. Allowing for their epicontinental nature, their early Proterozoic age (2.0‒2.4 Ga) and for their deformation by the 1.9 Ga Karelian event, we suggest that the Jatulian formations belong to the Belomorides. We propose to re-interpret the Belomorian fold belt in terms of a Wilson cycle as a collisional orogenic belt comprising a geosynclinal basin with oceanic crust (Tana and Granulite belts), an Archean reactivated basement (Belomorian gneisses) and a platform (Jatulian). The Belomorides represent the oldest fold belt in which a suture has been recognized and constitute an intermediate case between an intracontinental mobile belt orogeny and an active plate margin.