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Abstract
The geochronology of the metamorphosed bedrock of Blekinge, southeastern Sweden, has been investigated by U-Pb, Sm-Nd and Rb-Sr dating of whole rocks and minerals. A sample of acid metavolcanite from the Västanå formation, which has been assumed to be the oldest rock unit of the area, yields a U-Pb zircon age of 1705±8 Ma (2σ), and a sample of the ‘coastal gneiss’ from western Blekinge, thought to represent a more strongly recrystallized equivalent of the Västanå volcanites, yields a U-Pb age of 1690±39 Ma (2σ). The gneissic Tving granitoid in eastern Blekinge yields a U-Pb age of 1771±4 Ma (2σ). Together, these results suggest that the Blekinge province is not a southerly continuation of the Svecokarelian orogenic province of central Sweden. Instead it can be correlated with the Southwest-Swedish gneiss province, formed c. 1800–1650 Ma ago. The initial Sr and Nd isotope ratios suggest limited crustal prehistories for the source materials of the investigated Blekinge rocks. Rb-Sr whole-rock isochron ages of ‘coastal gneiss’ and granitoids from Blekinge range between 1760 and 1600 Ma, suggesting that the main metamorphism occurred in rather close connection with the rock forming events. Rb-Sr mineral ages vary between 1400 and 1200 Ma, indicating that the bedrock remained buried and sufficiently hot for Sr isotope exchange during several hundred million years.