Structure of the Otago schists

Abstract

The development of previous interpretations of the structure of the Otago schists is outlined. Structural terms are defined, metamorphic structures described, and their interrelations discussed. Mesoscopic folds and lineations in the central zone of schists trend north-west in East Otago, northerly in Central Otago, and easterly in North-west Otago. They plunge subparallel to the dip of the schistosity in the marginal steeply dipping schists. Three main classes of folds designated F₁, F₂, and F₃ are recognised, and are subdivided into a number of characteristic styles. The space and time relations of the mesoscopic folds suggest a sequence of phases of para-metamorphic deformation that may not have affected the terrain synchronously throughout, or everywhere to the same intensity. The regional structure appears to be a stack of nappe-like folds “overthrust” or “facing” eastward and north-eastward, flanked to the south-west and probably to the north-east by reclining and steeply plunging isoclinal folds.