Shear zones: Natural laboratories of rock deformation and mineral alteration

Robert Sturm (Austria) During the last few decades, the interest of diverse geosciences has increasingly focussed on the examination of so-called ‘shear zones’, because the displacements between two lithological blocks represent natural ‘laboratories’, within which the phenomena of mineral alteration and deformation are clearly shown for the purposes of scientific study. Many shear zones are only a few centimetres in size, meaning that their examination is relatively easy. Others, like the San Andreas Fault, have a width of several hundreds of metres, which requires a bit more effort to investigate (Fig. 1). Fig. 1. Some selected examples of shear zones with different dimensions: (a), (b) small-scale shear zones in the Zillertal/Austria, (c), (d) medium-scale shear zone in the Bohemian Massif/Austria, and (e) the San Andreas Fault. Shear zones – definitions and main characteristics Broadly speaking, along a shear zone, two lithological units – ranging in size from several square metres to the size of continentals – are displaced against each other. The movement has to be exclusively evaluated in terms of plate tectonics and often represents the cause of earthquakes. Depending on their orientation, three main types of shear zones can be distinguished (Fig. 2): The normal fault is characterised by the lowering of a lithological block with respect to its neighbouring tectonic unit. If the face of displacement between the two blocks has only a small angle of inclination, the shearing process is accompanied by crustal extension which is most impressively seen in the Rhinegraben and the East African … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.
%d bloggers like this: