Archaean elements of the basement outliers west of the scandinavian caledonides in Northern Norway: Architecture, evolution and possible correlation with fennoscandia

Abstract

Meso-and Neoarchaean basement rocks occur in two coastal outliers west of the Scandinavian Caledonides in North Norway, i.e. in western Troms (West Troms Basement Complex) and the Lofoten-Vesterålen area. When restored, these two outliers appear to have been assembled together in a cratonic-marginal position at the northern edge of the Fennoscandian shield in the Neoarchaean, and they share a similar tectono-magmatic history prior to Palaeoproterozoic events. This is confirmed by radiometric dating and similarity of sedimentary/volcanic units, intrusive/magmatic events, structural architecture and metamorphic events, and the mechanisms of amalgamation. Distinctive tonalite-trondhjemite-granodiorite (TTG) gneisses (2.92-2.67 Ga) and intervening meta-volcanic and sedimentary units, e.g. the Ringvassøya greenstone belt (2.83-2.6 Ga), make up a significant portion of the West Troms Basement Complex. The TTG gneisses, likely magmatic in origin, were deformed, metamorphosed up to granulite facies and locally migmatized during periods of accretion and collisional/convergent tectonism at c. 2.9-2.8 Ga, 2.75-2.7 and 2.7-2.67 Ga. The final Neoarchaean stage (c. 2.67 Ga) caused high-grade metamorphism, resetting and comprehensive migmatization along presumed Neoarchaean terrane boundary shear zones prior to intrusion of an extensive Palaeoproterozoic mafic dyke swarm (2.4-2.2 Ga). The subsequent Palaeoproterozoic evolution involved rifting and basin formation (2.4-1.9 Ga), intrusion of an extensive magmatic suite of anorthosite-mangerite-charnockite-granite (1.8-1.7 Ga) and Svecofennian accretion and collisional orogenesis at c. 1.8-1.67 Ga. In terms of correlation of the Archaean components with Fennoscandia and/or Laurentia, a closer connection to Fennoscandia is inferred from gravity-magnetic trends beneath the Caledonides, age constraints and tectono-magmatic evolution, and extrapolation of intervening tectonic basement windows present in the Caledonides. Provinces such as the Kola-Norwegian, Belomorian and Karelian provinces of the northwestern Fennoscandian shield of Russia, Finland and north Sweden, display obvious similarities with respect to supracrustal units of similar age and geological setting and their tectono-magmatic evolution.