Structural analysis of high-pressure metamorphic rocks of Svalbard: Reconstructing the early stages of the Caledonian orogeny

[1] The basement of Svalbard comprises several terranes that were assembled along NS-trending faults during the Caledonian orogeny. The NW and NE parts of Svalbard are considered to be derived from east Greenland, while SW Svalbard has affinities with Pearya, Ellesmere Island. High-pressure (HP) metamorphic rocks, such as eclogites and blueschists occur in west Svalbard and provide constraints on the history of the Caledonian convergence. The Motalafjella HP rocks display a geometry which is compatible with an initial dome structure sealed by Ordovician deposits. Retrogressed eclogites in Biscayarhalvoya appear in the uppermost unit of a nappe stack that formed in a constrictional deformation regime. The syncollisional exhumation of the eclogites was achieved before the deposition of Late Silurian conglomerates. The two field occurrences of HP rocks are interpreted with a detailed age review for the Svalbard terranes and a restoration of Svalbard paleogeography in the Devonian. We propose that the different tectonic events are part of a continuous Ordovician-Silurian orogenic sequence, predating the Scandian collision between Laurentia and Baltica. The closure of an ocean between Laurentia and a microplate was responsible for the formation and exhumation of the HP rocks of Motalafjella in the Ordovician, and later followed by the collision of the microplate with Laurentia in the Silurian. This orogenic phase can be considered as an equivalent of the Taconic orogeny in the Appalachians. The relative position of the Svalbard terranes and Greenland during this orogenic episode is constrained by strain directions measured in the field.