Petrography, structure and metamorphism of mélange rocks below the Jotun Nappe in Stølsheimen, Central South Norway

The Caledonian mélange unit of South Norway is a unit that has largely been overlooked in previously studies of the Caledonides. The mélange consists of Alpine type metaperidotite bodies now found as serpentinites, talc and serpentine conglomerate. The ultramafics are set in a metasedimentary matrix, together with some minor meta-basalt/gabbro units. The mélange has recently been identified as a separate tectonic unit and is believed to be remnants of a hyperextended margin, and challenges the traditional interpretation of the Scandinavian orogen. The unit is positioned structurally below the crystalline nappes previously assigned to the Middle Allochthon. Recent works have recognized that the Allochthone units of the Caledonian orogen have a much more complex relationship than previously believed. This thesis investigates the mélange unit at Selhamar, Stølsheimen in search of a more detailed description of the host rocks surrounding the ultramafic bodies in term of petrography, structures and metamorphism. The ultramafic bodies in the study area of this thesis are described in detail by Enger (work in progress). In Stølsheimen the mélange unit lies structurally between the Lower and Upper Bergsdalen nappes, underneath the Jotun Nappe Complex. The metasediments in the study area consists of metasandstone, metapelites and garnet micaschist, and are found together with some minor (garnet) amphibolite outcrops and slivers of gneissic rocks from the Upper Bergsdalen Nappe. The metasediments was exposed to upper greenschist to lower amphibolite metamorphic conditions (515-525oC and 7100-7450bars) during the Caledonian orogen. This is based on thermobarometric modelling by the use of the Theriak-Domino program suite together with bulk rock composition. The study area is dominated by top-to-the-NW shear direction and large scale folding, corresponding to Caledonian extension