Eurasian Arctic Tectonics: Geology of Severnaya Zemlya (North Kara Terrane) and Relationships to the Timanide Margin of Baltica

Sammanfattning: The North Kara Terrane (NKT), with Severnaya Zemlya as its main outcrop area, constitutes the Palaeozoic and older rocks of the northern part of the Kara Shelf. Potential field data suggest a continuation into the eastern Barents Shelf. Several lines of evidence imply that the NKT was a part of Baltica at least during the latter part of the Neoproterozoic, and probably was influenced by Timanian orogeny.The Timanide type area is characterised by metaturbidites from the pre-Timanian passive margin of the East European Craton (EEC). Regional amphibolite facies metamorphism, as exposed on Kanin Peninsula, was probably followed by near-isothermal decompression. It is inferred that these conditions were reached by depression beneath the accreted outboard terranes. Subsequently, the metaturbidites were thrust into their present position onto the EEC’s pericratonic unmetamorphosed shelf sediments. The thrusting was accompanied by rapid exhumation. About 560 Ma late-orogenic granites intrude the Timanian accreted terranes.On Severnaya Zemlya, Neoproterozoic turbidites, containing ca. 560 Ma zircons, are overlain by shelf deposits, which dominate the Palaeozoic until the end of the Silurian. The succession is interrupted by the regional Kan’on (canyon) River Unconformity and probably by a late Neoproterozoic unconformity. New U-Th-Pb ion-microprobe isotope-ages on volcanics and faunal evidence imply that the Kan'on River Unconformity developed in a short time span around the Cambrian-Ordovician boundary. Other isotope-ages demonstrate that intense igneous activity, which has been inferred to be related to rifting within the NKT, extended into the Arenig and was contemporaneous with the development of Baltica’s northeastern passive margin. Zircon xenocrysts (ca. 540 - 580 Ma) in these igneous rocks indicate a Timanian component in the crust below the Severnaya Zemlya Archipelago. In the latest Silurian, Old Red Sandstone facies sedimentation began with the migration of an inferred Caledonian foreland basin into the area of Severnaya Zemlya. The Caledonian deformation front overrode the area in the latest Devonian or earliest Carboniferous.The inferred late Caledonian deformation terminated, according to biostratigraphy and new isotope-ages from Bol'shevik Island granites, before the end of the Visean (ca. 345 Ma). Thus, the Uralian collision between the NKT and Siberia (ca. 300 Ma) apparently did not affect the Severnaya Zemlya Archipelago.