A revised geochronology for the Blekinge Province, southern Sweden

Abstract

Zircon grains from nine samples of metavolcanic rocks, gneisses, granitoids and migmatites from the Blekinge Province in southeasternmost Sweden have been dated by U-Pb using ion microprobe. The results suggest that most of the Blekinge bedrock was formed within a narrow time interval of 1.77-1.75 Ga, including the Västanå supracrustal formation and ʻcoastal gneissesʼ previously dated to c. 1.70 Ga. One sample, the 1.81 Ga Nättraby gneissic granite, appears to represent a sliver of slightly older proto-crust. An age of c. 1.75 Ga for an aplitic granite crosscutting the deformed Tving granitoids in eastern Blekinge brackets their deformation to between 1.77 and 1.75 Ga, whereas zircon grains of similar age from a migmatite neosome at Lindö may be inherited, making the result inconclusive. Thin metamorphic zircon overgrowths and resetting of the U-Pb system in titanite indicate a regional tectonothermal event at 1.45 to 1.40 Ga, accompanying the intrusion of the Karlshamn-type granites. The crust of the Blekinge Province thus was formed at 1.77-1.75 Ga from relatively juvenile sources in a subduction-related environment along the southern edge of Fennoscandia. It was deformed and partly uplifted relative to the undeformed TIB-1 granitoids of the Småland block further north, prior to the intrusion of the Karlshamn-type granites at 1.45 Ga.

U–Pb geochronology of gneisses and granitoids from the Danish island of Bornholm: new evidence for 1.47–1.45 Ga magmatism at the southwestern margin of the East European Craton

“…The presence of older inherited zircons with ages between 1.7 and 1.8 Ga, implies that the Bornholm granitoid magmas had been influenced by older crustal material. These zircon ages are similar to rock ages from Blekinge (Johansson et al 2006). No rocks of such old age have been found on Bornholm in this study, but it cannot be excluded that slices of such material are present within the gneiss package.…”

“…1) is often treated together as the BlekingeBornholm Block (BBB). The Blekinge region consists of 1.77-1.75 Ga subduction-related gneisses and granitoids (Johansson et al 2006), intruded by younger and less deformed granitoids with ages of around 1.45 Ga (Å berg 1988;Č ečys 2004;Č ečys and Benn 2007). In general, there is a trend of southwards younging crust formation in southeast Sweden, ranging from the 1.90-1.85 Ga Svecofennian province, through the 1.85-1.75 Ga Transscandinavian Igneous Belt, to the 1.77-1.75 Ga Blekinge province.…”

Trans-Baltic Palaeoproterozoic correlations towards the reconstruction of supercontinent Columbia/Nuna

“…Seismically, Bergslagen has also been traced in the middle and lower crust beneath the Ljusdal domain farther north (Korja and Heikkinen, 2005). Andersson (1997), Andersson et al (2004), Bergman et al (2008), Beunk and Page (2001), Hermansson et al (2007Hermansson et al ( , 2008, Högdahl and Sjöström (2001), Högdahl et al (2004), Johansson et al (2006, Krzeminska et al (2009), Lahtinen andNironen (2010), Lahtinen et al (2002Lahtinen et al ( , 2009a, Mansfeld et al (2005), Rutland et al (2001Rutland et al ( , 2004, Stephens et al (2009), Sultan et al (2005, Wikström and Andersson (2004), Williams et al (2008Williams et al ( , 2009). Fe-S-Si indicates the presence of various iron-and sulfide ore deposits.…”

“…1.81-1.76 Ga (TIB-1) granites in the East Småland domain of the Baltic Shield (e.g. Wikman, 1993Wikman, , 1997Johansson et al, 2006).…”

Hallandian 1.45Ga high-temperature metamorphism in Baltica: P–T evolution and SIMS U–Pb zircon ages of aluminous gneisses, SW Sweden

“…2) is made up of Paleoproterozoic 1.82-1.74 and Mesoproterozoic 1.47-1.44 Ga meta-intrusive rocks and gneisses, the older group also including meta-volcanic rocks (the Västanå association) and other gneisses of presumed supracrustal origin (Blekinge coastal gneisses; Fig. 2; Zariņš and Johansson, 2009;Johansson et al, 2006Johansson et al, , 2015. The 1.47-1.44 Ga igneous rocks are dominantly granitic-quartzmonzodioritic intrusions, which are partly well preserved (e.g., Eringsboda and Karlshamn intrusions;cf.Čečys et al, 2002;Čečys and Benn, 2007).…”