Where is greenschist found?

These ancient rocks are noted as host rocks for a variety of ore deposits in Australia, Namibia and Canada. Greenschist-like rocks can also be formed under blueschist facies conditions if the original rock (protolith) contains enough magnesium.

What happens to water during metamorphism?

Water pressures lower than the rock pressure cause metamorphic reactions to run at lower temperatures. Experiments have been made under water pressures less than the total pressure. Differences in the water pressure from rock to rock may produce reversals in the normal sequence of isograds.

What are metamorphic minerals?

Metamorphic rocks yield many attractive minerals, such as garnet, corundum (varieties of which include sapphire and ruby), and kyanite. The word ‘metamorphic’ comes from Greek and means ‘to change form’ and these rocks were originally igneous and sedimentary rocks that have been altered by heat and/or pressure.

How is greenschist made?

Greenschists form by regional metamorphism of mafic igneous rocks, usually basaltic rocks, under greenschist facies metamorphism (usually produced by regional metamorphism, typically 300–450 °C and 1–4 kilobars).

What does the presence of greenschist indicate?

The greenschist facies represents lower P-T conditions than the amphibolite facies, i.e., a lower metamorphic grade. Greenschist and amphibolite facies rocks form in typical regional metamorphism related to a geodynamic setting of continental collision tectonics (Figure 2).

What is metamorphic water?

Water driven out of rocks by metamorphism.

Do metamorphic rocks contain water?

Fluids present in the original rock or introduced from magma or high-temperature dehydration and degassing reactions, create metamorphic minerals containing constituents from water and gas molecules. Metamorphic reactions occur faster and at lower temperatures in the presence of water than under dry conditions.

What are 5 examples of metamorphic rocks?

Common metamorphic rocks include phyllite, schist, gneiss, quartzite and marble. Foliated Metamorphic Rocks: Some kinds of metamorphic rocks — granite gneiss and biotite schist are two examples — are strongly banded or foliated.

How metamorphic minerals are formed?

Metamorphic rocks form when pre-existing rocks (igneous, sedimentary, or metamorphic) are exposed to high temperatures and pressures under the Earth’s surface. Some pre-existing minerals, unstable at the higher temperature and pressure conditions, transform into new minerals. Others recrystallize and grow larger.

What minerals are found in eclogite?

Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other stable minerals—e.g., rutile. They are formed when volcanic or metamorphic rocks rich in such mafic minerals are subjected to extremely high pressures and moderate to relatively high temperatures.

What are the uses of eclogite rock?

Eclogites are helpful in elucidating patterns and processes of plate tectonics because many represent oceanic crust that has been subducted to depths in excess of 35 km and then returned to the surface.

What is in greenschist?

Greenschist is a fine- to medium-grained foliated metamorphic rock dominated by chlorite, actinolite and epidote, with or without albite, quartz and calcite.

What minerals are in the greenschist facies?

The more common minerals found in such rocks include quartz, orthoclase, muscovite, chlorite, serpentine, talc, and epidote; carbonate minerals and amphibole (actinolite) may also be present.

Where do metamorphic fluids come from?

Metamorphic fluid flow in the crust is probably initially widespread, as fluids are derived from much of the rock mass, and then becomes increasingly channeled as fluids are focused along higher-permeability layers or along structures such as faults or shear zones.

What are the three types of metamorphism?

The three types of metamorphism are Contact, Regional, and Dynamic metamorphism. Contact Metamorphism occurs when magma comes in contact with an already existing body of rock.

What is the characteristic mineral of metapelite?

Cordierite is the characteristic and dominant mineral in all metapelites from about 500°C upward, except in extremely Fe-rich rocks Photomicrograph showing textural evidence for the biotite breakdown reaction Bt + Qtz =  Opx + Kfs + H 2 O in a granulite from the Gruf Complex, Central Alps (picture diagonal 2mm).

What minerals are found in metapelitic protoliths?

Quartz usually dominates, and the amounts of other minerals depend on how much clay was in the protolith. Foliation, typical of metapelitic rocks, is usually lacking in these rocks because micas are generally absent. 8.51 Kyanite quartzite from Kapteeninautio, Finland. Sample is 28 cm across.

What type of metapelite forms at low grade?

At low grade this leads to the formation of chlorite and muscovite. At higher grade, biotite forms. Foliated textures develop as muscovite and biotite crystallize, so metapelites may be slates, phyllites, schists or gneisses depending on grade.

What happens when metapelites are partially melted?

Partial melting of metapelites produces a melt phase the so called neosome and leaves behind a refractory residue.