The Torlesse Composite Terrane is a plate tectonic
terrane
In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...
forming part of the
South Island
The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...
of New Zealand. It contains the Rakaia, Aspiring and Pahau Terranes and the Esk Head Belt.
Greywacke
Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...
(or Torlesse Greywacke) is the dominant rock type of the composite terrane;
argillite
:''"Argillite" may also refer to Argillite, Kentucky.''
Argillite () is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts ...
is less common and there are minor basalt occurrences. The Torlesse Composite Terrane is found east of the
Alpine Fault
The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island (c. 480 km) and forms the boundary between the Pacific Plate and the Indo-Australian Plate. The Southern Alps have been uplifted on the fa ...
in the
Southern Alps
The Southern Alps (; officially Southern Alps / Kā Tiritiri o te Moana) is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the range's western side. The name "Southern ...
of New Zealand. Its southern extent is a cryptic boundary with the
Caples Terrane Caples may refer to:
People
* Garrett Caples (b. 1972), American poet
* Harry Caples (1896 - 1933), Australian representative rugby league footballer
* Yvonne Caples (b. 1972), women's boxing champion
Place name
* Caples, Washington, United States ...
within the
Haast Schist
The Haast Schist, which contains both the Alpine and Otago Schist, is a metamorphic unit in the South Island of New Zealand. It extends from Central Otago, along the eastern side of the Alpine Fault to Cook Strait. There are also isolated outcrops ...
s in Central Otago. It is named for the Torlesse Range in
Canterbury
Canterbury (, ) is a City status in the United Kingdom, cathedral city and UNESCO World Heritage Site, situated in the heart of the City of Canterbury local government district of Kent, England. It lies on the River Stour, Kent, River Stour.
...
.
Description
The Rakaia Terrane rocks, of Permian to late Triassic age (300–200 Ma), occur south of
Rangiora
Rangiora is the largest town and seat of the Waimakariri District, in Canterbury, New Zealand. It is north of Christchurch, and is part of the Christchurch metropolitan area. With an estimated population of Rangiora is the 30th largest urba ...
. The Pahau Terrane rocks, of
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987.
In European lithostratigraphy, the name ...
to
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
age (160–100 Ma), occur to the north, and are probably derived from the Rakaia Terrane. At the boundary between these two terranes is the Esk Head Belt, an wide
mélange
In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically cons ...
of broken and deformed rocks. The Aspiring Terrane (Aspiring Lithologic Association) is officially included within the Torlesse Composite Terrane; however, it has a higher proportion of igneous rocks and a different sedimentary source.
Its original relationship with the Rakaia Terrane is obscured by the Haast Schist.
Deposition
The greywacke of the Torlesse Composite Terrane was deposited on the eastern side of New Zealand from the
Late Carboniferous
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
through to the Middle
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
. It was deposited in giant
deep sea fan
Abyssal fans, also known as deep-sea fans, underwater deltas, and submarine fans, are underwater geological structures associated with large-scale sediment deposition and formed by turbidity currents. They can be thought of as an underwater ve ...
s that extended beyond the ends of ancient submarine canyons. A fan starts with a
submarine canyon
A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to 5 km, from c ...
on the
continental shelf
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
. Then
turbidity current
A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. T ...
s rush down the canyon like giant undersea avalanches. They carry all sorts of sediments from the shallower
seafloor
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
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. These sediments may have derived in part from the
granitic
A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...
rocks of northeastern
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
, as suggested by studies of the mineral grains.
Metamorphism
The Torlesse Composite Terrane has undergone
metamorphism
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...
and been transformed into Haast Schist. In the Haast Schists, the
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s that make up greywacke became coarser grained and altered to other minerals including quartz, feldspar and biotite. Rare pods of
pounamu
Pounamu is a term for several types of hard and durable stone found in southern New Zealand. They are highly valued in New Zealand, and carvings made from pounamu play an important role in Māori culture.
Name
The Māori word , also used ...
(
jade
Jade is a mineral used as jewellery or for ornaments. It is typically green, although may be yellow or white. Jade can refer to either of two different silicate minerals: nephrite (a silicate of calcium and magnesium in the amphibole group of ...
) are found in the higher metamorphic grades near the Alpine Fault.
Fossil content
*
Torlessia
* Monotis
*
Hector's Ichthyosaur
*
Nothosaur
Nothosaurs (order Nothosauroidea) were Triassic marine sauropterygian reptiles that may have lived like seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about in length, with a long body and tail.F. v. ...
*
Conodont
Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...
[https://teara.govt.nz/en/fossils/page-2]
See also
*
Geology of the Tasman District
*
Stratigraphy of New Zealand
This is a list of the units into which the rock succession of New Zealand is formally divided. As new geological relationships have been discovered new names have been proposed and others are made obsolete. Not all these changes have been unive ...
**
Takaka Terrane
The Takaka Terrane is a Paleozoic terrane that outcrops in the South Island of New Zealand. It is most extensively exposed within the Kahurangi National Park in the Tasman District. The terrane is mostly made up of marble and volcanic rocks but i ...
**
Dun Mountain-Maitai Terrane
The Dun Mountain-Maitai Terrane comprises the Dun Mountain Ophiolite Belt (also called the Mineral Belt), Maitai Group and Patuki Mélange. The Dun Mountain Ophiolite is an ophiolite of Permian age located in New Zealand's South Island. Prehistori ...
References
{{Reflist
Further reading
* The Rise and Fall of the Southern Alps, G. Coates published 2002
Terranes
Geology of New Zealand
Paleozoic Oceania
Jurassic System of Oceania
Cretaceous System of Oceania
Geography of Canterbury, New Zealand
Geography of the Marlborough Region
Geography of Otago