Anisotropy in Precambrian Rocks and Post-Crystalline Deformation Models

Abstract

The influence of anisotropies in Precambrian rocks in Sweden on post-crystalline deformations is discussed. Schists, e.g. banded gneisses and metabasites, from the Gothenburg region are studied as steering, which can deviate from the main deformation pattern of the area. A post-crystalline deformation model of single shear type is discussed. Tectonic patterns as ac-planes, syn-tectonic to the grain fabric and B-axes are discussed as anisotropic steering elements at post-crystalline deformation. The anisotropy of a metamorphic rock is the inheritance from previous orogenic or serorogenic deformations or processes, manifested in the grain fabric of the rock. Later deformations, applied on the rock in solid state, will more or less inherit the previous pattern. This tectonic history of rocks, especially studied by means of petrofabric analysis and in regard to pre-crystalline, syn-crystalline and postcrystalline deformations, has been exhaustively studied by Sander (1930, 1948 and 1950) and his collaborators (Karl, 1964, Koark, 1959). formation model of postcrystalline ruptural deformation, multiple shear type. Slightly revised from I. Larsson (1963, p. 326). GEOGRAFISKA ANNALER * 49A (1967) * 2-4 The Precambrian rocks of Sweden are well suited for a study of the relationship between syn-crystalline and post-crystalline deformations of the rocks. The former may be investigated by means of the now classical methods of Sander, Gefiigenkunde (Sander, a.a.). Also the latter type of deformation may be depicted in the garb of petrofabric ideas and methods of Sander. The present author (1954) has studied the post-crystalline deformation pattern of an area in south Sweden and its relation to syncrystalline tectonic fabrics and has constructed a post-crystalline deformation model (1963, pp. 320-340). In this model all post-crystalline joints and fractures from a region of about 450 km2 are gathered. As this region, the province of Blekinge in south-east Sweden, may have suffered from several post-crystalline deformations during different orogenes (Subjotnian, Jotnian, Caledonian?, Hercynian?, Al-