A macroscopic recumbent fold in schist near Alexandra, Central Otago

Abstract

A zone of vergence change in mesoscopic folds has been mapped near Alexandra and is found to be associated with a zone of steeply dipping quartz-albite layering. This and other aspects of the pattern of mesoscopic structures are taken to indicate that schists of the Alexandra area are part of a large recumbent fold. The trace of its axial plane has been followed for 15 miles; the limbs appear to be at least several thousand feet thick. For the purposes of this work, meso scopic structures have been classified separately by type and age. Structures of similar type are not necessarily of similar age, and vice versa. Three age groups of metamorphic structures are recognised. The second of these groups is associated with the large recumbent fold. Mesoscopic structures belonging to this age group vary in type depending on their structural position in the large fold. Statistical analysis of folded lineations in two small areas suggest that axial-plane shear has been an important component of movement on the mesoscopic scale during the second phase of deformation. A direction of shearing is indicated that makes an angle of substantially less than 90° with the fold axes. © Taylor & Francis Group, LLC.