Lateral variations in supracrustal geology within the swedish part of the southern svecokarelian volcanic belt

Abstract

The southern volcanic belt of the Proterozoic Svecokarelian orogen exhibits significant lateral changes of lithology and stratigraphy. In the Swedish part of the belt, metavolcanites dominate the stratigraphic column to the west, whereas they form only minor interbeds in the predominant metasediments to the east. The metavolcanites of the western area are almost exclusively rhyolitic, while the eastern area also contains mafic and intermediate rocks. Mg-rich quartz-mica schists, which are believed to have been formed by synvolcanic alteration at depth, appear to be restricted to the western area. These features are compatible with an area of rhyolitic volcanic centres in the west supplying tephra into a sedimentary basin in the east. This episode of volcanism thus appears to represent an interlude in the deposition of sediments. It has been suggested that this rhyolitic volcanism originated from a continental crust which was activated by extensional tectonics.