Torlesse Greywacke

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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[edit]

Torlesse Greywacke was deposited on the eastern side of New Zealand from the Upper Carboniferous through to the Middle Cretaceous. It was deposited on giant undersea fans that extend around 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 collects all sorts of sediments from the seafloor. At the edge of the canyon the turbidity current spreads out and creates giant fans that blanket the old seafloor.

The Torlesse Greywacke may have been derived from the granitic rocks of northwestern Australia due to the large amount of quartz and feldspar it contains.

Metamorphism[edit]

The Torlesse Greywacke has undergone metamorphism and been transformed into Haast Schist. In the Haast Schists minerals that make up Torlesse Greywacke sometimes become visible. These minerals include quartz, feldspar and biotite.

References[edit]

  • The Rise and Fall of the Southern Alps, G. Coates published 2002