Baltica-Laurentia link during the Mesoproterozoic; 1.27 Ga development of continental basins in the Sveconorwegian Orogen, Southern Norway
Baltica-Laurentia link during the Mesoproterozoic; 1.27 Ga development of continental basins in the Sveconorwegian Orogen, Southern Norway
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (September 2002) 39 (9): 1425-1440
- absolute age
- Baltica
- continental drift
- continental margin
- dates
- Europe
- framework silicates
- Grenvillian Orogeny
- ion probe data
- Laurentia
- mass spectra
- Mesoproterozoic
- metamorphic rocks
- models
- Norway
- paleogeography
- plate tectonics
- Precambrian
- Proterozoic
- quartz
- reconstruction
- Scandinavia
- silica minerals
- silicates
- Southern Norway
- spectra
- subduction
- supracrustals
- Sveconorwegian Orogeny
- U/Pb
- upper Precambrian
- Western Europe
Recent models suggest that Laurentia and Baltica were contiguous during the Mesoproterozoic and shared a long-lived active continental margin, subsequently reworked during the Grenvillian orogeny. Around 1.25 Ga, the geological record is dominated by dyke-swarm intrusion, continental rift basin formation, A-type felsic magmatism, and arc - back-arc basin development. It points to a dominantly extensional tectonic regime over most of the craton and the Grenvillian margin, suggesting a retreating subduction boundary at that time. In the westernmost allochthonous domain of the Sveconorwegian Orogen, southern Norway, the Saesvatn-Valldal supracrustal sequences are interpreted as rift or pull-apart basins. They formed at and after 1.27 Ga, in a continental setting, at the margin of Baltica. This interpretation is based on geological, geochemical, and new secondary ion mass spectrometry (SIMS) zircon U-Pb data. A subvolcanic quartz porphyry at the base of the Saesvatn sequence yields a 1275+ or -8 Ma intrusion age. Metarhyolite samples in the lower part of the sequences yield equivalent extrusion ages of 1264+ or -4 Ma (Saesvatn sequence) and 1260+ or -8 Ma (Valldal sequence). The metarhyolite units are overlain by sequences of metabasalt and metasandstone. An angular unconformity between the metarhyolites and overlying rocks is locally observed and possibly reflects rift tectonics during formation of the basin. A sample of arkosic metasandstone at the top of the exposed Saesvatn sequence yields a few Archaean detrital zircon grains and a large spectrum of 2.2-1.2 Ga Proterozoic grains. These data point to a varied continental provenance and constrain sedimentation to later than 1211+ or -18 Ma.