Neoproterozoic palaeogeography in the North Atlantic Region:inferences from the Akkajaure and Seve Nappes of the Scandinavian Caledonides

• Published in: Precambrian Research
• Main Authors: Kirkland, C. L., Bingen, B., Whitehouse, M. J., Beyer, E., Griffin, W. L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: Greenland; Kalak; Lofoten; Svalbard; Fennoscandia; Fennoscandian; North Atlantic
• Online Access: https://researchers.mq.edu.au/en/publications/32d34e00-d37c-4c25-94e6-64e567207daf; https://doi.org/10.1016/j.precamres.2011.01.010; http://www.scopus.com/inward/record.url?scp=79952585522&partnerID=8YFLogxK

The Scandinavian Caledonides exposes increasingly far travelled nappes upwards (westwards). The Lower- to Middle Allochthon are widely regarded as indigenous to the pre-Caledonian margin of Baltica (Fennoscandia), while higher thrust sheets (e.g. lower Upper Allochthon) have more controversial ancestries. Recent studies have suggested that thick early-Neoproterozoic (Tonian-Cryogenian) metasedimentary sequences hosted in thrust sheets of the Scandinavian, Greenland, British and Svalbard Caledonides represent two cycles of sedimentation along the peri-Rodinia (Laurentia-Baltica) margin of the supercontinent; alimented by erosion of the Grenvillian and Sveconorwegian orogenic belts. To test and expand this model, we report zircon U-Pb and whole rock Sm-Nd data from orthogneisses and siliciclastic metasediments in a transect from the (para)autochthonous Dividal Group, through the crystalline Middle Allochthon Akkajaure Nappes and into the overlying Seve Nappes (lower Upper Allochthon).The Akkajaure Nappe Complex (Middle Allochthon) is dominated by Precambrian crystalline rocks, of granitic to dioritic composition, that yield ages of 1788 ± 6, 1806 ± 15, and 1876 ± 10 Ma. These rocks are thrust over an imbricated basement (Lower Allochthon), which contains rocks of similar age, including a rhyolite dated at 1790 ± 6 Ma. The ages and Nd isotope chemistry of these rocks are identical to those from other Fennoscandian basement units and imply derivation from west of the Lofoten islands. A sample of sediment, originally attributed to the lowest unit of the overlying Seve Nappe Complex, has a detrital population dissimilar to all other Seve-Kalak Nappe samples and has a significant 1800. Ma volcanic component. This sediment was intruded by granite at 1797 ± 4. Ma. Its provenance and rapid depositional timing indicates it is better considered as part of the tectonically captured Fennoscandian basement (Middle or Lower Allochthon).Metasediments from higher Seve nappes, in Jämtland, were deposited after 730. Ma and contain ...