| Abstract: | Tectonic slides are faults that have been described and discussed in the Caledonides for over fifty years but which, possibly because of misunderstanding, have failed to find acceptance in structural schemes elsewhere. A review of the literature suggests, nevertheless, that they are a distinct class of fault common in certain terrains. Unlike the usual ‘brittle’ faults, slides occur in metamorphic conditions as an integral part of the more widespread fabric producing regional deformation that characterises metamorphic—orogenic belts. Because of their formation in such ‘ductile’ environments, slides are broadly concordant structures which are rarely associated with cataclasis. Since they also often lie along lithological contacts, they may be very difficult to detect at outcrop — despite the large displacements that may have taken place. Slides however may be recognised by (a) tectonic schist, and (b) their typical occurrence in planar zones of intensified regional deformation. They are often associated with major folds: either occurring in individual fold limbs or else cutting across the axial planes of fold pairs or groups of folds. Alternatively they may be unrelated to folds and may occur at simple lithological junctions or else separate rocks of widely different orogenic history, i.e. at tectonic fronts. Strain studies suggest that lithological contacts are important in initiating slides because of the different response of contrasting rock types to high strains. |
