Proterozoic crustal evolution in southcentral Fennoscandia

• Main Author: Appelquist, Karin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2010
• Subjects: Transscandinavian Igneous Belt; TIB; Eastern Segment; Habo Volcanic Suite; Malmbäck Formation; U-Pb zircon ion probe dating; Nd isotopes; geochemistry; Hallandian; Danopolonian; Fennoscandia; Fennoscandian
• Online Access: http://hdl.handle.net/2077/21530

The Transscandinavian Igneous Belt (TIB) and the Eastern Segment of the Southwest Scandinavian Domain reflect advanced stages of continental growth within the Fennoscandian Shield. The relationship between the two units is not clear, mainly because N-S trending shear zones of the Protogine Zone transect the border zone. The main goal of this thesis has been to investigate rocks in the border zone and to conclude how these rocks differ from each other. In this work two volcanic sequences and 24 granitoids in the border area, near Jönköping, were examined. The thesis reports geochemical and Sm-Nd isotope data as well as U-Pb ion microprobe zircon dates for extrusive and intrusive rocks in the southwestern part of the TIB and intrusive rocks in the eastern part of the southern Eastern Segment. The TIB rocks are subdivided into TIB-0, TIB-1 and TIB-2 groups based on their ages. In this work, the Habo Volcanic Suite and the Malmbäck Formation are dated at 1795±13 Ma and 1796±7 Ma respectively, which establishes that they are part of the TIB-1 volcanic rocks. The Malmbäck Formation is situated in the southwestern part of TIB, east of the Protogine Zone, whereas the Habo Volcanic Suite is located c. 50 km northwest of the Malmbäck Formation, between shear zones of the Protogine Zone. Both suites comprise mafic to felsic components and the Malmbäck Formation includes one of the largest mafic volcanic rock units of the TIB-1. The Malmbäck Formation comprises fairly well preserved volcanic rocks, with primary textures, although mineral parageneses in some rocks suggest metamorphism at up to epidote-amphibolite facies conditions. Amphibolites facies metamorphism and deformation has largely obscured primary textures of the Habo Volcanic Suite. Dating of a Barnarp granite which intrudes the Habo Volcanic Suite gave an age of 1660±9 Ma, corresponding to TIB-2. The occurrences of Malmbäck Formation megaxenoliths within TIB-1 granitoids are explained by stoping. Geochemical signatures of the two metavolcanic rock suites suggest ...