Crystallographic fabrics and deformation histories

Abstract

Report of a meeting of the Tectonic Studies Group held on 19 May 1986 at the Department of Earth Sciences, Leeds University. The meeting was organized by R. D. Law, R. J. Knipe, S. Bowler and G. E. Lloyd. This meeting was arranged to reflect the recent resurgence of interest in the relationships between deformation histories and crystallographic fabric development in plastically deformed rocks. This resurgence of interest has been due largely to recent advances in both mathamatical modelling of fabric development and the development of analytical techniques for measuring crystallographic preferred orientation. The meeting was attended by some 40 participants, of whom 75% came from either mainland Europe or North America. The meeting was opened by S. M. Schmid who presented a general introduction to: (1) the principles of crystallographic preferred orientation (fabric) development, 2) recent advances in analytical techniques for the measurement of crystallographic fabrics, and (3) calcite fabric development associated with experimental simple shear deformation. In this introductory paper the importance of integrating microstructural and crystallographic fabric studies was emphasized. Such integrated studies within quartz mylonite belts indicate significant departures from plane strain (simple shear) deformation. This theme was followed by Behrmann who reviewed recently published petrofabric evidence from the Moine thrust zone and Betic Cordilleras for partitioning of deformation within thrust sheets into domains of non-coaxial and essentially coaxial flow. Behrmann argued that this type of deformation, which incorporated sub-vertical shortening and movement parallel stretching, may be a reflection of gravity induced spreading of the