Lithostratigraphy and structure of the Caples terrane of the Humboldt Mountains, New Zealand

Abstract

Schistose lithostratigraphic units, correlated with non-schistose rocks of the Caples terrane, can be mapped successfully along the western margin of the Haast Schist terrane in the Humboldt Mountains of north-west Otago. The rocks include chert, volcanogenic sediment and lava of the Harris Saddle Formation; the mineralogically immature Momus Sandstone; the new Cosmos Formation, a thin but persistent horizon of green volcanogenic sandstone; and the overlying pelitic and psammitic rocks of the Upper Peak unit, the Mystery Pelite (new), and the Bold Peak unit. They have been reconstituted under metamorphic conditions of the pumpellyiteactinolite and greenschist facies.Three pe1iods of deformation are recognised. The first, synmetamorphic phase resulted in a maior recumbent fold, with an axial surface parallel to the regional schistosity; the second, post-metamorphic phase is defined by folded schistosity and deformed isotects. Maior structures of both fold episodes have been verified by direct obse1vation. Penecontemporaneous faulting was an important adjunct to postmetamorphic folding. In a third deformational episode the Greenstone Melange, a chaotic rock unit containing a variety of igneous, metamorphic, and sedimentary rocks, was emplaced, possibly diapirically, along a narrow extensional zone in the east.Rocks of the Caples terrane grade northwards and eastwards into the Haast Schist terrane which in turn grades eastwards into Torlesse rocks. Caples and Torlesse rocks are petrographically and lithologically distinct; the Haast Schist thus appears to represent a metamorphosed amalgamation of these two rock suites.

Structure of schist in the Mt Aspiring region, northwestern Otago, New Zealand

“…The schists ofthe Mt Aspiring area lie between the schists at Cromwell (Turnbull 1981) and the Alpine Schist studied by Cooper (1974). Structures in lower-grade rocks to the west of the Mt Aspiring area have been described by Bishop et al (1976), and structures in lower-grade rocks to the east have been outlined by Norris & Cooper (1977). The objects ofthe present study are to describe the structures and their superposition in the schists ofthe Mt Aspiring area, and to attempt to correlate these structures with those of surrounding areas.…”

Integrating earth and life sciences in New Zealand natural history: The parallel arcs model

“…The Haast Schist Group represents a regionally metamorphosed sector defined texturally (Bishop et al 1976), and best exposed in Otago (over some 26 000 km2) where it lies between, and grades into, the Caples terrane to the southwest and the Torlesse terrane to the northeast. Other assemblages, such as that represented by the Aspiring terrane (Norris & Craw 1987) were probably also involved in the formation of the Haast Schist.…”

New radiolarian age information for the Chrystalls Beach Complex, southwest of Dunedin, New Zealand

“…As emphasised by various authors (e.g., Bishop et al 1976), typical terrigenous sandstones of the Caples Terrane differ from those of the Torlesse Terrane in that they are mostly lithic-volcaniclastic rather than quartzofeldspathic of inferred continental source. This difference demands spatially separate sedimentary basins and source regions.…”

“…This difference demands spatially separate sedimentary basins and source regions. It implies that the Torlesse Terrane is allochthonous and has probably moved at least hundreds of kilometres from its depositional source to a position oceanward of Caples and other New Zealand terranes (Bishop et al 1976;Coombs et al 1976;MacKinnon 1983).…”