Feldspar Pb isotopic compositions from northern Fennoscandia and their application to characterising and correlating Palaeoproterozoic terranes.

The Palaeoproterozic Lapland-Kola Orogeny in northern Fennoscandia sutured the Archaean Karelia and Kola or Murmansk cratons (Daly et al., 2006). The suture zone comprises a collage of terranes which importantly include juvenile Palaeoproterozoic belts that indicate that these cratons were once separated by oceanic lithosphere. Extension of the Lapland-Kola Orogeny more widely within Columbia is important for palaeogeographic reconstructions of Baltica with Laurentia, e.g., Park (2005). Contrasting reconstructions (Evans, 2013) underscore the inherent difficulty in differentiating between the various simultaneously developing orogens and cratons.

The Pb isotopic compositions of feldspars are a valuable tool for understanding Precambrian crustal evolution. Being time-invariant (due to low U and Th contents), these data can readily distinguish terranes with different early geological histories which have been affected by later orogeny. This study has combined published and new outcrop data from northern Fennoscandia with new detrital K-feldspar Pb isotopic data from sandstones and modern rivers from the same region in order to evaluate the application of this technique to Archaean and Proterozoic terrane correlation within the Columbia supercontinent