A four-phase model for the Sveconorwegian orogeny, Fennoscandia, and the Sveconorwegian-Grenville correlation
|Location||International Geological Congress,oslo 2008|
|Holding Date||07 October 2008|
The Sveconorwegian Belt of Fennoscandia is classically restored to the east of the Grenville Belt of Laurentia, facing Amazonia, at the end of the Mesoproterozoic. Accordingly, the Grenvillian-Sveconorwegian orogeny is interpreted as an oblique collision between a common Laurentia-Fennoscandia margin and the Amazonia indenter. The Sveconorwegian Belt divides, from east to west, into the Paleoproterozoic parautochthonous Eastern Segment, and four Mesoproterozoic allochthonous terranes: the Idefjorden, Kongsberg, Bamble and Telemarkia Terranes. The Idefjorden terrane formed during the 1660-1520 Ma Gothian accretionary event, while the Telemarkia Terrane formed during the Telemarkian 1520-1480 Ma continental arc magmatism. The terranes are possibly endemic to Fennoscandia, though an exotic origin for the Telemarkia Terrane is possible.
Sveconorwegian assembly of these units is divided into four phases. (1) At 1140-1080 Ma, the Arendal phase represents the collision between the Idefjorden and Telemarkia Terranes, which produced the Bamble and Kongsberg tectonic wedges. This phase involved accretion of an outboard volcanic arc, high-grade metamorphism in the Bamble and Kongsberg Terranes, peaking in granulite-facies conditions at 1140-1125 Ma, and thrusting of the Bamble Terrane onto the Telemarkia Terrane at 1090-1080 Ma. (2) At 1050-980 Ma, the Agder phase corresponds to the main oblique continent-continent collision. It resulted in burial of the Idefjorden Terrane to HP amphibolite- to granulite-facies conditions (>1.0 GPa) at 1050 Ma, followed by exhumation. Crustal thickening in the Telemarkia Terrane led to granite magmatism starting at 1050 Ma and up to granulite-facies metamorphism starting at 1035 Ma. (3) At 980-970 Ma, the Falkenberg phase reflects final convergence in the belt, shortly followed by divergence. Foreland propagation of the orogeny resulted in burial of the Eastern Segment to eclogites-facies conditions at 970 Ma. (4) Between 970 and 900 Ma, the Dalane phase corresponds to gravitational collapse of the belt. It is associated with post-collisional magmatism, exhumation of a core complex in the Eastern Segment, and exhumation of the Rogaland-Vest Agder Sector in the Telemarkia Terrane as a wide gneiss dome. This dome culminated at 930 Ma with LP-HT granulite-facies metamorphism and intrusion of an anorthosite-mangerite-charnockite complex.
Recent data provide three new key correlations between the Sveconorwegian and Grenvillian belts, supporting classical reconstructions. (1) The 1520-1480 Ma Telemarkian magmatism is coeval with the Pinwarian magmatism in the Grenville LP Allochthonous Belt. (2) The 1510-1490 Ma Rjukan Group and overlying Vindeggen Group in the Telemarkia Terrane correlate with the Wakeham Group in the LP Allochthonous Belt. (2) The 1050 Ma HP metamorphism in the Idefjorden Terrane (Agder phase) correlates with the 1080-1040 Ma HP, up to eclogite-facies, metamorphism in the HP Allochthonous Belt (Ottawa phase).