Metamorphic evolution of the crust of south-western Norway

Thesis

Part of the Western Gneiss Region (WGR) of Norway has been mapped in western Sognefjord. Five major tectonostratigraphic units underlying low-grade Devonian metasediments have been recognized: the Basement Gneisses (BG), Lower, Middle, and Upper Mafic Units (LMU, MMU, UMU), and Hyllestad Schists (HS). All the units have been affected by polyphase deformation. Five different styles of deformation have been recognized across the field area, representing up to five discrete tectonic episodes.

Eclogite facies mineral assemblages have been found in the BG, either forming mafic pods or as relicts in garnet amphibolites. Temperature and pressure conditions of metamorphism in all units have been estimated using various calibrated reactions. Temperatures range from about 400°C to 700°C and pressures from about 4 kbar in post-D₂ assemblages to 15 kbar in eclogites. Estimated conditions of eclogite formation are consistent with regional studies.

High-pressure (eclogitic) conditions have also been inferred from mineral textures in the highest unit (Hyllestad Schists). Mineral assemblages in parts of this unit may represent pressures as high as 14 kbar at temperatures of 600°C.

It is suggested that the Mafic Units and HS are allochthonous and were emplaced onto the WGR during an early stage of the Caledonian Orogeny. All units, including the Basement Gneisses, have suffered retrogression during a late extensional phase which continued into at least the Middle Devonian.

Authors: Bailey, D; Bailey, David Elliott

• Alternative title: an example from Sognefjord
• Publication date: 1989
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Metamorphism (Geology); Sogne Fjord (Norway); Earth; Metamorphic rocks; Norway; Crust