A Sveconorwegian deformation zone (system?) within the Eastern Segment, Sveconorwegian orogen of SW Sweden ‐ a first report

Abstract

A recently recognized, more than 10 km wide deformation zone (the Ullared Deformation Zone, UDZ) can be followed for at least 30 km from the Mylonite Zone southeastwards into the Eastern Segment of the Sveconorwegian orogen of SW Sweden. The deformation affects a heterogeneous, high‐grade metamorphic gneiss complex, with locally preserved eclogite relics. The deformation is characterized by a strong, locally mylonitic, gneissosity, with a subhorizontal or moderately E‐ or ESE‐plunging stretching lineation. Deformational fabrics are related to metamorphic decompression and retrogression, and kinematic indicators show a top‐to‐the‐east and dextral sense of shear. Protolith ages (zircon) of pre‐ and post‐tectonic rocks bracket the age of deformation in the eastern part of the UDZ between c. 1380 and 955 Ma, but metamorphic mineral ages suggest an upper age limit of c. 1000 Ma. The deformation in the western part of the UDZ is contemporaneous with or younger than that in the eastern part. The deformation is suggested to be related to Sveconorwegian late‐orogenic extensional processes.

Möller, C., Andersson, J., Söderlund, U. & Johansson, L., 1997: A Sveconorwegian deformation zone (system?) within the Eastern Segment, Sveconorwegian orogen of SW Sweden ‐ a first report. GFF, Vol. 119 (Pt. 1, March), pp. 73–78. Stockholm. ISSN 1103–5897.

Keywords:

• Deformation zone
• high‐grade metamorphism
• granulite
• eclogite
• mylonitic gneiss
• stretching lineation
• tectonic lenses
• zircon ages
• granite
• decompression
• retrogression
• extension
• Mylonite Zone
• Ullared
• Eastern Segment
• Sveconorwegian orogen