Folds of the Mount Cook National Park, New Zealand, and their origin under a wrench regime acting in a subduction zone

Abstract

A MAP is presented of some of the macroscopic and mesoscopic folds in the Triassic arkosic and quartzitic greywacke suite of the Mt Cook National Park between Mt Sefton and Mt Elie de Beaumont, and a number of the folds are described and named. It is shown that the folds have extremely attenuated limbs and possibly thickened hinge zones. The hinge-zones are steeply plunging, generally facing north-east, some facing and plunging south-west over at least part of their length. Small south-plunging macroscopic folds belong to class 3 of Ramsay (1967); small north-plunging folds to class 1A. The folds were probably formed at the same time as the schists, at a higher tectonic level, in the upper part of a subduction zone developed during the Rangitata Orogeny. A marked structural discontinuity recognised by E. O. Macpherson separates the schists and greywacke rocks and structures from the strata and structures of the Mesozoic and Upper Paleozoic sediments to the west, in the Southland, Nelson, and South Auckland Synclines. The folding is tentatively related to the movement of New Zealand under a wrench regime of continental displacement.