Quartz-plagioclase metasomatic rocks in the Västervik area, southeastern Sweden

Sr–Nd isotope and geochemical characterisation of the Paleoproterozoic Västervik formation (Baltic Shield, SE-Sweden): a southerly exposure of Svecofennian metasiliciclastic sediments

“…The metasediments studied are complementary to the 'soda metasomatites', with removal of Sr (being geochemically similar to CaO) and introduction of K 2 O (being geochemically equivalent to Rb). In addition, Elbers and Hoeve (1971) describe the mobility of SiO 2 in this context that is corroborated by the recent study described by Vollbrecht and Leiss (2008) that interprets some of the orthoquartzites, especially those in the vicinity of late anatectic diapirism, as being arkosic metasandstones transformed to quartzites by the formation of secondary quartz due to SiO 2 input. The observed disturbance of the Rb-Sr isotope system with initial values below BABI for all orthoquartzites analysed in this study could thus be correlated to this above-described transformation.…”

“…In addition, unaltered plagioclase was detected in some of these samples that indicate later growth during or after the metamorphic overprint. Present accessory phases include the following: sillimanite, cordierite, andalusite and minor occurrences of garnet indicative for HT/LP metamorphism as already stated by Elbers and Hoeve (1971), Kresten (1971a, b), Hoeve (1978) and Gavelin (1984). A sample of the so-called Black Sand (Gavelin 1984), presumably representing a heavy-mineral alluvial deposit and a metapelitic sample showing a garnetrich peak metamorphic assemblage, was also selected.…”

“…Hence, it seems that ancient removal of common Sr in these rocks by fluids and possibly secondary input of Rb is responsible for the observed pattern, thus leading to exceptionally high present-day Sr isotope ratios by radiogenic ingrowth with time. Some 5-10 km north-east of the study area quartz-plagioclase rocks of metasomatic origin are exposed, the so-called soda metasomatites of Elbers and Hoeve (1971) and Hoeve (1978). These authors inferred removal of K 2 O and introduction of CaO into the metasediments during metasomatism possibly connected to the HT/LP overprint of the Västervik area.…”

“…Shortly, after the end of sedimentation, the Västervik formation subsided to a depth of around 10 km and suffered an intense HT/LP metamorphic overprint (Elbers and Hoeve 1971;Kresten 1971a, b;Gavelin 1984;Beunk and Page 2001). This high-grade metamorphic event presumably led to the formation of migmatites, diatexites and in situ production of voluminous S-type granitic melts (Kresten 1971a, b;Gavelin 1984).…”

“…This high-grade metamorphic event presumably led to the formation of migmatites, diatexites and in situ production of voluminous S-type granitic melts (Kresten 1971a, b;Gavelin 1984). Probably related to the metamorphism, the Västervik area suffered a Na-Ca metasomatic overprint leading to the formation of plagioclase-rich rock types (the so-called soda metasomatites of Elbers and Hoeve (1971) and Hoeve (1978)) in close vicinity of the Loftahammar granites. In the southern part of the study area (Misterhult archipelago), a presumably metasomatic rock type called 'Rheosome' is described by Kresten (1971a, b).…”