TECTONIC SETTING AND PROVENANCE OF NEOPROTEROZOIC ELEMENTS IN THE SCANDINAVIAN CALEDONIDES

While the Grenville Orogeny in Laurentia reached its conclusion by about 1000 Ma the Sveconorwegian Orogeny in Baltica remained active until about 900 Ma. In the autochthonous basement of southwestern Scandinavia this period was characterized by compressional events, leading to the formation of eclogites at ca. 970 Ma in Sweden, extension, and especially widespread magmatism, forming granitoid crust and local anorthosite and mafic dyke complexes. In the allochthons of the southern Caledonides there are numerous crystalline nappes with protolith ages of 1700 to 1250 Ma, strongly affected by deformation, metamorphism and magmatism between 1000 and 900 Ma. The Jotun and Lindås nappe complexes, for example, were invaded by anorthosite and related rocks at ca. 970 Ma, underwent high temperature metamorphism, plutonism and deformation between 950 and 930 Ma, with late metasomatic overprints as late as 900 Ma. These terranes were likely positioned in the middle to lower crust at the edge of Baltica. By contrast, adjacent nappes comprise 960-950 Ma gabbro and tonalite and related supracrustal rocks, but only exhibit moderate metamorphic grades. They were likely formed in an upper crustal setting. These late Sveconorwegian magmatic suites may have a relation to the widespread ca. 1000-900 Ma clastic sedimentary successions now dispersed in allochthons of Scandinavia, Svalbard, East Greenland and the British Isles, and attributed by Cawood and coworkers to deposition in the Asgard Sea which opened by the rotation of Baltica from Laurentia. The highest nappes of Central Norway include Grenvillian rock likely derived from the Grenville Orogen. The Kalak nappes of northern Norway comprises ca. 1000 Ma clastic sedimentary successions metamorphosed and intruded by 980-960 Ma granites. Other parts of the sedimentary succession are somewhat younger and were affected by repeated orogenic events at 870-800 Ma, 720-680 Ma and ca. 600 Ma which caused high grade metamorphism, deformation and plutonism. Such events are not known in the Baltic Shield, thus their provenance is most likely from peri-Gondwanan regions. The latest event to affect these nappes, the emplacement of the Seiland Igneous Complex at ca. 570 Ma, could also have some link to the Timanian Orogen which accreted on the northeastern margin of Baltica between 600 and 500 Ma.