Where do mylonites come from?
Mylonite is a metamorphic rock formed by ductile deformation during intense shearing encountered during folding and faulting, a process termed cataclastic or dynamic metamorphism.
What are mylonites in geology?
A mylonite can be defined as a cohesive foliated rock (on which linear fabric is also commonly observed) produced by tectonic reduction of grain size through crystal-plastic processes in restricted areas of intense deformation. From: Developments in Structural Geology and Tectonics, 2019.
Where can you find Blueschist?
This is a ‘low temperature, high pressure’ prograde metamorphic path and is also known as the Franciscan facies series, after the west coast of the United States where these rocks are exposed. Well-exposed blueschists also occur in Greece, Turkey, Japan, New Zealand and New Caledonia.
What is a Granoblastic rock?
Granoblastic is an adjective describing an anhedral phaneritic equi-granular metamorphic rock texture. Granoblastic texture is typical of quartzite, marble, charnockites and other non-foliated metamorphic rocks without porphyroblasts.
Where is greywacke found?
Greywacke is a variety of argillaceous sandstone that is highly indurated and poorly sorted. It comprises a large percentage of the basement rock of New Zealand, and so is an important rock type throughout the country.
Where does gneiss come from?
Gneiss is a metamorphic rock formed by changing schist, granite, or volcanic rocks through intense heat and pressure. Gneiss is foliated, which means that it has layers of lighter and darker minerals. These layers are of different densities and come about as a result of the intense pressure used to form gneiss.
Where is gneiss found in Canada?
The Canadian Shield, the largest expanse of Precambrian rocks on Earth, is host to Earth’s oldest known rock – the Acasta Gneiss of the Slave Province of the Shield, located about 300 kilometres north of Yellowknife, Northwest Territories.
Is blueschist found in subduction zones?
THE high-pressure, low-temperature metamorphic rocks known as blueschists have long been considered to form in subduction zones, where the descent of a relatively cold slab leads to the occurrence of unusually low temperatures at mantle pressures.
Is blueschist high grade?
Very Low- to Low-Grade Metamorphism of Mafic Rocks at Medium-High Pressure—Blueschist. At very low to low-temperature (250–500 °C) and medium-high pressure (> 8 kbar), mafic rocks are generally metamorphosed to form blueschist, which contains the blue Na-rich amphibole—glaucophane.
How is granoblastic texture formed?
Granoblastic texture is the typical texture formed in metamorphic rocks when grains mutually adjust their boundaries in the solid state in an attempt to achieve textural equilibrium.
Is marble an Aphanitic?
Foliation is common in aphanitic as well as phaneritic metamorphic rocks….
| Metamorphic Rocks | APHANITIC OR PHANERITIC |
|---|---|
| Fine- to coarse-grained, GRANOBLASTIC texture | |
| MINERAL CONTENT – Examples of minerals that you might find | CALCITE DOLOMITE |
| ROCK NAME | MARBLE |
| PROTOLITH (Original Rock) | Limestone Dolostone |
What kind of rock is metaconglomerate?
Metaconglomerates are conglomerates that have experienced some metamorphism. Conglomerates are detrital sedimentary rocks, meaning they were formed from the weathered remains of other rocks.
Where is greywacke found in NZ?
Greywacke forms the older basement rocks of the eastern part of the South Island and the higher non-volcanic mountains of the North Island. The hills and coast of the Wellington region are made of greywacke.
How was greywacke formed NZ?
Over 200 million years, tens of thousands of metres of these sediments built up off the edge of Gondwana. They were eventually buried, deformed and hardened to become the rocks known as the Torlesse greywackes. Today, Torlesse rocks make up more than half of the New Zealand landmass.
What kind of rock is gneiss?
metamorphic rock
gneiss, metamorphic rock that has a distinct banding, which is apparent in hand specimen or on a microscopic scale. Gneiss usually is distinguished from schist by its foliation and schistosity; gneiss displays a well-developed foliation and a poorly developed schistosity and cleavage.
Does gneiss come from granite?
Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. It is formed by the metamorphosis of granite, or sedimentary rock. Gneiss displays distinct foliation, representing alternating layers composed of different minerals.
How are mylonites formed?
Mylonites are ductilely deformed rocks formed by the accumulation of large shear strain, in ductile fault zones. There are many different views on the formation of mylonites, but it is generally agreed that crystal-plastic deformation must have occurred, and that fracturing and cataclastic flow are secondary processes in the formation of mylonites.
Where can I find mylonite in Alaska?
Similkameen, west of the Okanogan valley. [48.984645,-119.398584] 88_015. Mylonite in syenite with large feldspars. Similkameen, west of the Okanogan valley. [48.984645,-119.398584]
What is the difference between mylonite and ultramylonite?
Mylonites with larger grain size are sometimes described as gneisses and very fine-grained ultramylonites may resemble slate. Mylonites usually have a quartzo-feldspathic protolith (like granite or gneiss) although they may originate from any rock type.
What type of metamorphic rock is mylonite?
Mylonite is a foliated metamorphic rock that is composed of intensely flattened minerals in a fine-grained streaked matrix. Mylonites form deep in the crust where temperature and pressure are high enough for the rocks to deform plastically (ductile deformation).