Contractional kink bands formed by stress deflection along pre-existing anisotropies? Examples from the Anglo-Brabant Deformation Belt (Belgium) and the North Dobrogea Orogen (Romania)

Kink bands within two slate belts, the Anglo-Brabant Deformation Belt (Belgium) and the North Dobrogea Orogen (Romania), reveal similar problems with respect to linking kink band geometries to expected palaeostress directions. In the North Dobrogea Orogen, the two opposite kink band sets of two different systems of conjugate kink bands develop for a wide variety of cleavage orientations. In the Anglo-Brabant Deformation Belt, the occurrence of the two opposite kink band sets of a conjugate kink band system opposes the expected occurrence. In both cases, this can be attributed to stress deflection along a pre-existing anisotropy. Moreover, the presence of kink bands in the North Dobrogea Orogen with curving kink axes (and curving kink band boundaries) also puts doubt on the direct relationship between kink band geometry and stress.The idea of stress deflection along a pre-existing anisotropy and the strong control of the pre-existing anisotropy on the kink band geometry and orientation has important implications for the use of kink bands as regional palaeostress indicators. Depending on the relative intensity and relative orientation of the pre-existing fabrics (here bedding and cleavage), different mechanisms of kink band development may operate. Depending on the mechanism, different solutions in terms of inferred palaeostress direction may exist.