ROTATIONAL QUANTITIES IN HOMOGENEOUS FLOW AND THE DEVELOPMENT OF SMALL-SCALE STRUCTURE

A summary discussion is given of attempts to quantity the degree of non-coaxiality of rock flow from observations of rock structure, and of some principles governing the sensitivity of structure to non-coaxiality. This is preceded by an extended review of relevant terminology, since some of the current confusion about rotational features in rocks stems from confusion about basic concepts and terminology from continuum mechanics. The kinematic vorticity number has been estimated for naturally deformed rocks from three localities. These yield vorticity numbers ranging from 0.35 to 0.9, corresponding to flows intermediate in character between pure and simple shearing.