Structural history of the Bygdin area, Oppland.

Abstract

The tectonic history of the area, which is part of the marginal thrust zone of the Norwegian Caledonides, is described. Within the area, the Upper Jotun Nappe has been thrust over the Valdres Sparagmite and the Bygdin Conglomerate during the first Caledonian movement phase recognized in the area (F1). This thrusting induced cataclastic textures in the nappe rocks and the sediments, and during a late phase of the F1 deformation, produced north-west trending linear structures, including the pebble elongation of the Bygdin Conglomerate. During the second movement phase (F2) a large nothwest trending antiform, the Bygdin Antiform, was produced which refolded the basal thrust plane of the Jotun Nappe. The axial trend of the minor structures associated with this antiform is exactly parallel to that of the first movement phase. Structures of the third movement phase (F3) are found only on the minor scale and have an orthorhombic symmetry similar to those described in the Moine Thrust Zone, Scotland. During the last movement phase in the area (F4), brittle structures which include joints, joint-drag folds, and tension gashes were formed.