Vorticity analysis in shear zones: A review of methods and applications

Quantitative vorticity analyses in naturally deformed rocks are essential for studying the kinematics of flow in shear zones and can be performed using a range of methods, which have been developed over the last two decades. The purpose of this review is to act as a starting point for the reader who needs a current overview of the existing methods and to indicate in what circumstances these methods can be most suitably applied. The review begins by providing an overview of deformation theory, followed by description of the most promising methods – in terms of assumptions, analytical procedures, and possible sources of uncertainty. Finally, the methods are compared on the basis of their uncertainties and strain memory, and discussed in terms of how they can be used to retrieve information about temporal and spatial variation of flow vorticity in shear zones. This review confirms that, although the existing methods are valuable, they are at an immature stage of development and suffer from limitations and uncertainties leading to interpretational problems, which, at present, can be alleviated by applying as many methods as possible to a given sample. Additional studies are recommended to advance the development of existing and new methods.