Summary
The finite strains within the thrust sheets of the Moine Thrust Zone in NW Scotland have been factorized into components of simple shear and longitudinal strain. Variations in these strains have been examined in the Cambrian sediments in the Eriboll and Assynt areas and strain maps produced of the Glencoul Nappe, Assynt. There are heterogeneous simple shear strains parallel to the layering resulting from bending of the nappe over a step in the thrust plane and to frictional drag at the base of the thrust. Layer parallel shortening and associated layer parallel thickening occur in the front of the thrust zone at Eriboll, above a decoupling plane in the lower part of the Cambrian sequence. Within the Cambrian rocks of the Glencoul Nappe in Assynt, there is a steady eastward increase in intensity of layer parallel shortening togeather with local anomalous zones characterized by more intense shortening or extension. These anomalous zones overlie shear zones in the Lewisian basement. There are variations in shear strain on the plane which contains the normal to bedding resulting from differential movement of the nappe. These shear strains distort and fold the bedding planes. Combinations of these shear strains and the longitudinal strains result in a wide range of ellipsoid shapes from oblate to prolate and also explain the pattern and sequences of folds in the nappes and mylonite belts. The folds are formed by local variation in shear and longitudinal stress and, hence, there may be no simple correlation of fold phases along, or across, a thrust zone.
- © 1981 The Geological Society
References
Strain within thrust sheets
