Metamorphic Structures in Part of the Eastern Otago Schists

Abstract

Structures in part of the eastern Otago schists have been separated into several descriptive types and mapped accordingly. Structures have also been identified as products of four deformational phases and mapped on this basis. Phase II and III structures predominate. Mesoscopic folds, lineations, and s-surfaces developed during the phase II deformation in conjunction with formation of macroscopic folds. Phase III structures, not represented by macroscopic folds, include most of the mesoscopic types of the preceding deformation, but are considerably more variable in style and orientation. The only first-phase structure recognised is a schistosity; the only fourth-phase structure is a fine crenulation of micas.The orientation of large stratigraphic units has been determined in numerous localities by tracing contacts between units of contrasting lithology and by measuring the orientation of tabular bodies defined by schist tor ridges. These data along with observations of mesoscopic structures are used to construct a tectonic profile showing the macroscopic structure along a narrow belt extending about 25 miles in the Deep Stream — Nenthorn Stream area. The structure is dominated by one major recumbent fold closing to the south-west and having subsidiary macroscopic folds in the hinge area and on the upper limb.