Torlesse Greywacke
Torlesse Greywacke is a type of sedimentary rock. It is a hard and rather drab grey sandstone that is found in New Zealand. Torlesse Greywacke is found east of the Alpine Fault in the Southern Alps of New Zealand. It lies between the western edge of the Haast Schists and the Canterbury Plains, and is named for the surveyor Charles Torlesse.
Deposition
Torlesse Greywacke was deposited on the eastern side of New Zealand from the Upper Carboniferous through to the Middle Cretaceous. It was deposited in giant undersea fans that extended beyond the ends of ancient submarine canyons.
A fan starts with a submarine canyon in the continental shelf. Then turbidity currents rush down the canyon like giant undersea avalanches. As it does this it carries all sorts of sediments from the shallower seafloor of the continental shelf. At the end of the canyon the turbidity current spreads out and creates giant fans of sediment that blanket the deep seafloor.
That the Torlesse Greywacke was derived from the granitic rocks of northeastern Australia has been suggested by detailed studies of the mineral grains.[1]
Metamorphism
The Torlesse Greywacke has undergone metamorphism and been transformed into Haast Schist. In the Haast Schists, the minerals that make up Torlesse Greywacke became coarser grained. These minerals include quartz, feldspar and biotite.
References
- The Rise and Fall of the Southern Alps, G. Coates published 2002