A SVECONORWEGIAN DEFORMATION ZONE (SYSTEM-QUESTIONABLE) WITHIN THE EASTERN SEGMENT, SVECONORWEGIAN OROGEN OF SW SWEDEN - A FIRST REPORT

A recently recognized, more than 10 km wide deformation zone (the Ulla red Deformation Zone, UDZ) can be followed for at least 30 km from the Mylonite Zone southeastwards into the Eastern Segment of the Sveconor wegian orogen of SW Sweden. The deformation affects a heterogeneous, h igh-grade metamorphic gneiss complex, with locally preserved eclogite relics. The deformation is characterized by a strong, locally myloniti c, 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 easter n 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 i n the eastern part. The deformation is suggested to be related to Svec onorwegian late-orogenic extensional processes.