Emplacement of a Silurian granitic dyke swarm during nappe translation in the Scandinavian Caledonides

摘要

This paper investigates the geometry, deformation history and age of the synkinematic granitic Ardal dyke complex in the Upper Jotun Nappe, SW Norway. The typically subparallel north-trending dykes are folded and boudinaged, reflecting emplacement and deformation in a top-to-southeast non-coaxial strain field. The synmagmatic strain field is interpreted to reflect thrusting of the nappe at 427 ± 1 Ma, the zircon U-Pb TIMS age of the Ardal dyke complex. The Upper Jotun Nappe is a displaced part of the Baltic Shield; the age is therefore a minimum age for initiation of Caledonian thrusting of crystalline Baltica crust in western Norway.