Permian (map symbol Y)

Distribution
Sedimentary rocks of Permian age are present in the north of the South Island and in a broad band extending from northwestern Otago through Southland to the east coast, south of Dunedin. Permian igneous rocks have a similar distribution. It is thought that Permian rocks exist offshore to the west of Kawhia and Taranaki. A separate group of Permian sedimentary rocks, part of the greywacke belt, occurs in north Otago, south Canterbury, Marlborough, central North Island and the Bay of Islands (see Greywacke).

Content
The first group of sedimentary rocks mentioned above have a very high content of volcanic-derived fragments (volcanogenic), but are otherwise quite variable. In the Nelson area they include fossiliferous conglomerate, sandstone, mudstone and limestone, some slightly metamorphosed. Interbedded tuff and more rarely layers of basalt are also found. A very similar sequence occurs in northwestern Otago and northern Southland.

Volcanic rocks are intimately associated with sedimentary rocks in both the Nelson and Southland regions, although they are more prominent in the south where they form the bulk of the Takitimu Mountains and extend in a thin band north through the Eglinton and Hollyford valleys. The volcanics comprise basalt, andesite, porphyry, volcanic breccia, tuff, and minor interbedded sediments.

The Permian greywacke rocks consist of hard grey sandstone and darker coloured mudstone (see Greywacke).

Ophiolite

The Permian time period is also represented by an association of rocks known as an ophiolite assemblage, composed of deep water sediment, submarine basalt, and very basic plutonic rocks occurring in long narrow belts. These rocks represent a slice of sea floor that made up an old subduction zone. The Permian ophiolite assemblages are recognised in Nelson and Otago. In Nelson the plutonic rocks comprise gabbro, dunite (named from Dun Mountain), peridotite, and serpentinite. In this area some parts of the original layered plutonic complex have been deformed by later tectonic events so as to break up into large blocks in a chaotic manner. This chaotic mass is called a melange and is characterised by the widespread occurrence of serpentine. The melange belt extends to the north and south of the recognised ophiolite sequence of the Dun Mountain-Red Hills area. In northwestern Otago the ophiolite assemblage is best seen at Red Mountain which is composed of peridotite, dunite, and serpentinite, and extends south and east in a belt. In both areas the assemblage is known as the Dun Mountain Ophiolite Belt, and lies adjacent to Permian sedimentary rocks.

The basic plutonic complexes of the Longwood Range and Bluff are of Permian age. These comprise gabbro and peridotite as the main rock types, and are probably associated with the volcanics of the Takitimu Mountains.

At Parapara Peak, northwest Nelson, is an important occurrence of Permian freshwater and shallow marine rocks which have no volcanic content.

Paleogeographic conditions
Following the events of the Tuhua Orogeny, which formed new continental crust on the edge of Gondwanaland, a volcanic arc developed offshore. To the east of the arc a marine sedimentary basin developed. Some Permian rocks were deposited on the edges of this basin, close to the volcanic arc, and rocks with a lesser volcanic content were deposited in deeper water and further from the arc. A subduction zone east of the continental margin was actively drawing down oceanic crust, causing the volcanic activity and a trench to develop above it. The "fossil" subduction zone is represented by the Dun Mountain ophiolite belt. The small area of rocks at Parapara Peak represents deposition adjacent to the continent to the west of the subduction zone.

The Permian greywacke rocks were deposited in a different setting from the volcanogenic rocks, as they have different mineral content and rock detritus. The setting was either a different part of the marine basin mentioned above, or a different part of the ocean floor altogether. The source of the rock detritus may have been the lands that later became Australia or Antarctica. The different Permian rock types were later brought together by tectonic movements.

Deformation
Some of the Permian rocks are part of a major downfold (syncline) structure also involving the younger Triassic and Jurassic rocks in Nelson and Southland. Within the major structure the rocks are commonly tightly folded with steep dips. Locally there are areas of shearing and major faulting. The greywacke rocks are also very deformed, with many crush zones and faults, and some have been metamorphosed into schist.