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 f~lding, 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 p<;>rtion ofthe fault has been reactivated during later (slxth phase?) deformation possibly associated with Alpine Fault movement.

Lead isotope constraints on the origin of Cenozoic orogenic gold systems in the Southern Alps and northwestern Otago, South Island, New Zealand

“…Lamprophyre emplacement was related to the development of folds and extensional fractures associated with the Moonlight Fault during the inception of the Alpine Fault as a through-going plate boundary structure . Most dikes, especially in the southern portion of the swarm, fill a conjugate set of extensional fractures that strike east and southeast and have steep dips (Craw 1985;Cooper et al 1987). Dikes at the northern end of the swarm also fill northeast-striking fractures that are parallel to the structural grain of the host rock, imposed by tight folding of the foliation at the northern extension of the Moonlight Fault zone Craw et al 2003).…”

The relationship between the Hyde‐Macraes Shear Zone, deformation episodes, and gold mineralisation potential in eastern Otago, New Zealand

“…Craw (1985) demonstrated in west-central Otago the penetrative cleavage was S 2 with related structures including a mineral elongation and isoclinal intrafolial folds. This interpretation is taken here to extend to eastern Otago, from microscopic evidence of an early foliation.…”

“…D 3 structures are correlated with the Manorburn Generation (Norris 1977) in their type area in west-central Otago, and are believed to have formed in the final stages of metamorphism (Craw 1985;Suggate et al 1978, table 5.1, p. 337). Kink and chevron folds with a semibrittle style are designated as D 4 or D5 (Craw 1985). The structural nomenclature adopted here is displayed in Table 1, after Means (1966), Norris (1977), Suggate et al (1978), Craw (1985), Teagle (1987), , and Teagle et al (1990).…”

“…A third deformation resulted in macroscopic recumbent folds and mesofolds in S 2 which generally lack a penetrative fabric (Means 1966). D 3 structures are correlated with the Manorburn Generation (Norris 1977) in their type area in west-central Otago, and are believed to have formed in the final stages of metamorphism (Craw 1985;Suggate et al 1978, table 5.1, p. 337). Kink and chevron folds with a semibrittle style are designated as D 4 or D5 (Craw 1985).…”

“…Kink and chevron folds with a semibrittle style are designated as D 4 or D5 (Craw 1985). The structural nomenclature adopted here is displayed in Table 1, after Means (1966), Norris (1977), Suggate et al (1978), Craw (1985), Teagle (1987), , and Teagle et al (1990).…”