Serpentinite-bearing metasedimentary complex near Lesja and relationship with the hyperextended pre-Caledonian margin of Baltica

Serpentinite-bearing metasedimentary complex near Lesja and relationship with the hyperextended pre-Caledonian margin of Baltica Orlando Quintela, Johannes Jakob and Torgeir B. Andersen CEED, University of Oslo In the Scandinavian Caledonides, a serpentinite-bearing metasedimentary complex has been investigated for its complex lithological association and enigmatic tectono-stratigraphic position. It comprises a large number of meta-peridotite bodies as well as detrital serpentinites. These ultramafic rocks are associated with meta-sandstones, mica schists and locally mafic lithologies. In the study area near Sjongsvatnet north of Lesja in south central Norway, the serpentinite-bearing metasedimentary complex is represented by the Sjongsæter Group. It is structurally positioned in the Blåhø Nappe, which overlies the Sætra Nappe, that is laterally correlated with the Seve Nappe Complex. The Sjongseter Gp. comprises a serpentinite sheet at its base, overlain by metasediments including serpentinite conglomerates, mica- and quartz-rich schists and phyllites, as well as amphibolite bodies and mafic schists. Some metaperidotites are truncated by mafic dykes. To the west, the Sjongseter Gp is infolded with the structurally lower basement of the Western Gneiss Region. The structural pattern is defined by map- to outcrop-scale east-west-trending folds that interfere with northwest-southeast-trending folds, and by east-northeast plunging mineral and stretching lineation. The structural evolution of the serpentinite-bearing complex is characterized by polyphase deformation and metamorphism during the Scandian phase of the Caledonian Orogeny and late- to post-orogenic extension, as observed from the interfering folds and lineation pattern. A similar serpentinite-bearing metasedimentary complex has previously been reported from the Bøverdalen, Stølsheimen and the Bergen Arcs. It has been suggested that this unit is the vestiges of a hyperextended segment of the Baltican margin, based on comparison with ancient and modern analogues such as the Alps, Pyrenees and the Iberian margin. It has also been suggested that this unit may be traceable at the same structural level towards Lesja, and the Røros area. The lithological resemblance between the serpentinite-bearing complexes to the SW and and the Sjongseter Gp is is evident. In the Lesja area, however, the original stratigraphy of sediments on exhumed mantle is preserved. The new observation presented here support the previous correlation of the serpentinite-bearing unit across southern Norway, and that this unit in the study area contains more mafic material compared the melange in the SW.