Structure of schist in the mt aspiring region, northwestern otago, new zealand

Abstract

Five phases of deformation are recognised in the schists of the Mt Aspiring area, northwest Otago, New Zealand.The first two phases resulted in isocIinal ductile folding and macroscopic nappe formation during greenschist facies metamorphism. The third phase, which occurred during waning metamorphic conditions, resulted in tight folding, with east-west overthrusting of macroSCOPIC nappes.Ouring this third phase, earlyformed fold axes in high-strain zones were rotated towards the stretching or translation direction. The fourth deformation phase is characterised by chevron folds (on all scales) with north-trending axes and associated west-dipping thrust faults.The Moonlight Fault, a major regional feature.is associated with this phase of deformation. The fifth phase of deformation involved mesoscopic conjugate sets of crenulations with east- and southeasttrending axes. Steeply dipping, fold axial surface joints developed in these crenulations are commonly intruded by lamprophyric dikes or associated carbonate veins.Several phases of deformation have characteristic quartz c-axis fabrics. The Moonlight Fault has been traced northwards from Shotover River to Burke River. North of Wilkin River, orientation and character ofthe fault change from a north-striking, west-dipping fault to a northeast-striking vertical fault. This northern portion ofthe fault has been reactivated during later (sixth phase?) deformation possibly associated with Alpine Fault movement. © 1985 Taylor & Francis Group, LLC.