Table of Contents
Textures and Microstructures
Volume 5, Issue 1, Pages 1-17

Ductile Shear Bands in a Naturally Deformed Quartzite

1Centre Armoricain d'Etude Structurale des Socles, CNRS, Université de Rennes I, Avenue du GI Leclerc, Rennes Cédex 35042, France
2Department of Geology, Royal School of Mines, Imperial College, London SW7 2BP, United Kingdom

Received 1 May 1981; Accepted 29 June 1981

Copyright © 1982 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Microscale shear bands are features that often occur oblique to the mylonitic foliation in mylonites. This paper is concerned with such structures within a quartz-mylonite. Geometrical features, microstructures and fabrics associated with shear bands are described. Both optical and transmission electron microscopy have been used. It was observed that the development of shear bands is closely related to (i) the onset of dynamic recrystallisation during deformation, (ii) a change of bulk deformation within the mylonites from relatively homogeneous to inhomogeneous and (iii) a marked softening of the mylonite. Across shear bands, dominant deformation mechanisms change from a dislocation creep type to grain boundary sliding. This induces strong modification of quartz lattice preferred orientations. The asymmetry of quartz fabrics due to shear should generally be favoured by the development of shear band structures. Our results indicate that the production of ductile shear band structures helps to accommodate large strain deformations at low temperatures. Results also indicate that grain and sub-grain sizes are not affected by variations in strain rate.