Solitary mantle peridotite bodies in Stølsheimen, Central South Norway

• Main Author: Enger, Anders Stanes
• Format: Master Thesis
• Language: English
• Published: 2016
• Subjects: geology; mantle; peridotites; hyperextension; Bergsdalen; Blackwall; Norway; Rauberget; Newfoundland
• Online Access: http://hdl.handle.net/10852/50179; http://urn.nb.no/URN:NBN:no-53839

In the last few years the tectonostratigraphic model of the Caledonides has been revised, to account for among others the melange unit discussed in this thesis. This unit, which in the past have been overlooked, consist of deep marine schists, Alpine-type meta-peridotites, soapstone, serpentinites, dertrial serpentinites, gneisses and conglomerates. The classical way of looking at the meta-peridotites are as the lowermost portion of ophiolites, but the rest of the ophiolite stratigraphy, the sheeted dike complex and the pillow basalt, are not seen in this case. A revised model for the meta-peridotites was presented in 2012 by Andersen et.al. They proposed that the meta-peridotites were remnants of exhumed mantle at the pre Caledonian magma poor passive margin of Baltica formed during hyperextension. In this study two such Alpine mantle peridotites are studied, The Rauberget and Vetle Rauberget situated in Stølsheimen in Central South Norway sitting structurally below the Jotun Nappe complex and sandwiched in-between the Upper and Lower Bergsdalen Nappe complex. The peridotites are severely serpentinized, which is confirmed by petrography, no primary mineralogy is found. At the borders of the meta-peridotites blackwall alteration zones and talcified rims can be seen. The whole-rock geochemistry shows a high content of Mg and Si, and a low content of Ca and Al. The Mg and Si-content can be explained by the serpentinization process. While the Al-content points in the direction of depleted mantle origin. The trace element content of the peridotites is really low, commonly below the detection limit of the ICP-MS, which implies a dunitic origin of the peridotite. Based on this information any classification of the meta-peridotites original tectonic environment is difficult. In order to evaluate the hyperextension hypothesis the rocks surrounding the meta-peridotites were compared with rocks seen at the present day passive margin Iberia-Newfoundland and remnants of hyperextension in the Alps and the Pyrenees.