Strain analysis of polyphase deformed conglomerate from the Sunnhordland region, west Norway

A conglomerate zone within the Lower Palaeozoic sequence in the south western part of the Norwegian Caledonides has been deformed twice by penetrative deformation. From a strain analysis on deformed pebbles it was possible to separate the flattening tectonic strain (5/2.9/1), caused by the second deformation from an earlier tectonic fabric of axial ratio, 2.85/1.87/1; the latter was presumable the result of the first deformation. The first deformation was responsible for a shortening of the rock across the schistosity surface by 43 percent, white the total shortening assuming the second deformation being almost coaxial with the first, is around 56 percent. Parallelism of pebble elongation and fold axis at the hinge zone, which are otherwise oblique, is explained by a special coincidence of pebble fabric axes and second deformation strain axes.