Structural and lithological continuity and discontinuity in the Otago Schist, Central Otago, New Zealand

Abstract

The Otago Schist in Central Otago has undergone complex late metamorphic and post‐metamorphic deformation during uplift and exhumation. Two late metamorphic structural generations can be recognised and these may be genetically related. The earlier Manorburn Generation has been widely recognised and described previously. This generation has fold axes subparallel to a prominent syn‐metamorphic quartz rodding lineation. A later generation, herein named Poolburn Generation, has folds which superficially resemble Manorburn Generation, but has fold axes that are at a high angle to the quartz rodding lineation. Both generations occur in mappable fold zones (kilometre‐scale) that are generally not vergence boundaries, and some minor relative displacement may occur across fold zones. Fold zones occur within structurally and lithologically uniform schist domains. Abrupt changes in lithological sequences and orientations of structural elements such as Manorburn and Poolburn Generation fold axes and quartz rodding lineations occur at post‐metamorphic faults which separate different schist domains. Central Otago schist can be subdivided on the regional scale (tens of kilometres) into at least nine schist domains whose structural and lithologic continuity is disrupted by fault discontinuities. The domains and bounding discontinuities developed during Late Jurassic and Early Cretaceous uplift. Syn‐metamorphic compressive ductile deformation evolved to localised fold zones in the early stages of this uplift. Subsequently, regional extension caused juxtaposition of domains with different textural zones, and schists from slightly different structural levels. The Caples/Torlesse Terrane boundary is a composite feature, and different segments formed at different stages through the transition from ductile compression to brittle extensional deformation.