Geology and petrochemistry of weakly metamorphosed rocks in the upper Wakatipu district, southern New Zealand

The late Paleozoic and Mesozoic quartzo-feldspathic Canterbury Suite contains a wide range of detrital lithotypes and facies, representing many depositional environments. The stratification, sedimentary structures, and fossils characteristic of 11 lithotypes are described and interpreted in terms of probable depositional environments.Fifteen recognisable faunal zones represent only part of the total time span of the Canterbury Suite (Carboniferous to late Jurassic). There is no record of early Permian, latest Permian and early Triassic, or latest Triassic through middle Jurassic, except for a single collection representing the Ururoan Stage (early Jurassic). All but two of the faunal assemblages consist mainly of epifaunal and nektonic species of low abundance and diversity. Infaunal species are virtually absent. The assemblages are characteristic of continental shelf environments.Marginal marine and non-marine depositional environments, coarse detrital conglomerates, and vascular plant material are common in the eastern part of the outcrop area. Thev become less abundant towards the west, and in the extreme west of the outcrop area, conglomerate is essentially absent, plant fossils very sparse, and probable deep marine facies relatively common. These trends show that the detritus was transported from east to west, and that the source rocks lay east of present-day New Zealand. Conglomerate and sandstone composition shows that during Triassic time the source area consisted of granodiorite and minor schistose and gneissic metamorphic rocks, but that by late Jurassic time acid volcanic rocks were also abundant.

Section: Terminologymentioning

confidence: 99%

Lithological and paleontological content of the Carboniferous-Jurassic Canterbury Suite, South Island, New Zealand

Andrews¹,

Speden²,

Bradshaw³

1976

“…Although it is possible that the difference is due to a contrast in original material, it is more probable that some Fe 2 0 J has been reduced to FeO during low grade metamorphism. In this respect Kawachi (1974) notes that schists in Otago and the Southern Alps, thought to be metamorphosed Torlesse and Caples rocks, generally have higher FeO /Fe Z 0 3 ratios than the equivalent unmetamorphosed sedimentary rock. The average FeO/Fe 2 0 g ratio for the schists (6'7) is similar to that of the Greenland Group.…”

Section: Mg and Transition Elementsmentioning

confidence: 99%

Geochemistry of the Greenland Group (early Ordovician), New Zealand

Nathan

1976

The Greenland Group is a uniform quartz-rich greywacke-argillite sequence, of early Ordovician age, characterised by the following geochemical features: K20 > Na20, CaO < 1· 5%, Rb~ Sr. These features reflect the distinctive mineralogy of the Greenland Group, which contains little feldspar or volcanic detritus and appears to consist of varying proportions of two end-members, quartz and clay, with little other clastic material. Lower Ordovician rocks elsewhere in New Zealand and south-east Australia are also reported to be distinctively quartzose, and can be expected to have similar geochemical characteristics. The mineralogical and geochemical maturity of the Greenland Group suggests that It is polycyclic (but derived originally from a plutonic source), and that the parent rock for the final cycle was a widespread quartzose sedimentary or metasedimentary unit.

“…Although the ,'rea was visited by McKay (1881) and Park (1887), and subsequently Benson (in Benson & Holloway 1940) described rocks collected by Holloway, and Grindley (1958) produced a 1: 253 440 reconnaissance map, little detailed stratigraphic or structural information was available until the Upper Wakatipu area, immediately to the south, was mapped by Kawachi (1974). Kawachi recognised a steeply dipping, eastward-facing sequence apparently faulted against presumed older schists in the east.…”

Section: Previous Workmentioning

confidence: 99%

“…The lowest two correspond to the oldest two of the informal units recognised by Kawachi (1974) and are upgraded to formation status. Lateral facies variations and complications introduced by the Rock Burn Fault have prevented satisfactory correlation of our mapping units with the remainder of the units proposed by Kawachi. With some reluctance therefore we have named the new formations and nominated reference sections from the well exposed sequence of the present area.…”

Section: Stratigraphymentioning

confidence: 99%

“…Caples Group in west Otago, and Pelorus Group in Nelson (see Carter et al 1974), the belt separates the schist terrane from the Dun Mountain Ophiolite Belt or, in its absence, from the volcanoclastic rocks of the Hokonui Assemblage. Recent work in the Caples terrane* (Kawachi 1974;Turnbull 1974) has highlighted the petrographic contrast between the mainly volcanogenic provenance of Caples rocks and the plutonic-metamorphic provenance of the Torlesse greywackes on the opposite side of the Haast schists. (I), and its relationship to areas of previous workers: (2) Kawachi (1974); and (3) Turnbull (1974).…”

Section: Introductionmentioning

confidence: 99%

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

Bishop¹,

Bradshaw²,

Landis³

et al. 1976

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.