Linear fabrics in the Bergsdalen Nappes, southwest Norway: implications for deformation history and fold development

Linear structures in the Bergsdalen Nappes fall into two temporally distinct categories. The most pronounced linear set formed during large-scale Caledonian thrusting of the overlying Jotun Nappe and other nappes on to Baltoscandia. Parallelism between stretching, ribbon, mineral and intersection lineations supports previous interpretations of a close correlation between the trend of this lineation and the direction in this area. A simple model of combined thrusting and horizontal pure shear with maximum extension in the ftow direction is sugges ted, which explains the parallelism between fold axes and lineations, as well as the predominantly constrictional strain. The lineation pattem formed during thrusting indicates an overall east-southeast displacement vector, but local deviations between the different sheets and between the Bergsdalen Nappes and the Western Gneiss Region may reftect slip partitioning in addition to later reworking by extensional reversed movement of the overlying Jotun Nappe. A less pervasive set of previously neglected linear structures in the Bergsdalen Nappes marks this post-orogenic reversed movement with a top-to-the- WNW sense of shear.