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)

Abstract

a b s t r a c tKink 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.

Conjugate, Riedel-shear vein arrays: A new type of en echelon vein system

“…Two main observations, however, suggest that the vein arrays studied in this paper did not form as a result of kink band development but that the kinking instead is reflecting non-coaxial deformation associated with the pre-existing vein arrays. Firstly, a symmetrical conjugate pair of kink bands forms when the maximum compressive stress during kinking is subparallel to the foliation (Ramsay and Huber, 1987;Srivastava et al, 1998;Debacker et al, 2008). The two sets of kink bands form in the obtuse angle with the maximum compressive stress and are mutually separated by a dihedral angle of ca.…”

Kink bands in thrust regime: Examples from Srinagar–Garhwal area, Uttarakhand, India

“…The effort in palaeostress analysis was also extended to single sets of kink bands (Clifford 1968). Debacker et al (2008) cautioned using kink bands to deduce regional palaeostress patterns and suggested that one should not extrapolate the inferred palaeostress outside the region under study.…”