Caledonian nappes of southern Norway and their correlation with Sveconorwegian basement domains

Abstract This paper summarizes the main geochronological features of the Caledonian nappes in southern Norway, discusses their similarities and differences, and reports new U–Pb isotope dilution thermal ionization mass spectrometry data. The latter include ages of 1670 Ma for orthogneiss from the Upper Finse Nappe, 1500, 1250 and 950 Ma for intrusive rocks from the Hallingskarvet Nappe, and 1037 and 997 Ma for volcanic units from the Suldal and Lower Finse nappes. The Caledonian nappes can be subdivided into units formed at 1700–1600 Ma, having an affinity with Gothian crust, and units formed at about 1500 Ma, correlating with Telemarkian crust. A Sveconorwegian tectonometamorphic overprint is ubiquitous, but with large differences in the intensity and relative timing of the overprint. Some complexes (such as Kvitenut–Dyrskard) were affected at around 1000 Ma and others (such as Jotun and Lindås) between 970 and 930 Ma. There is also considerable variety in the Caledonian effects. Ordovician events affected some nappes (Jæren, Revsegg), thought to be of exotic origin, while Silurian and Devonian events of variable intensity are observed in all nappes. The emerging patterns offer the basis for a qualitative discussion of the provenance of the nappes that can eventually be combined with quantitative structural criteria to reconstruct pre-Caledonian palaeogeographies.