Is greenschist high-grade?
Is greenschist high-grade?
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 greenschist rock?
Greenschist. A schistose metamorphic rock whose green color is due to the presence of chlorite, epidote, or actinolite; a common product of low-grade regional metamorphism of pelitic or basic igneous rocks.
What is greenschist for?
In Minoan Crete, greenschist and blueschist were used to pave streets and courtyards between 1650 and 1600 BC. These rocks were likely quarried in Agia Pelagia on the north coast of central Crete. Across Europe, greenschist rocks have been used to make axes.
What metamorphic grade is Muscovite?
Medium-grade metamorphism takes place at approximately at 320–450 ºC and at moderate pressures. Low grade hydrous minerals are replaced by micas such as biotite and muscovite, and non-hydrous minerals such as garnet may grow.
How do you identify a greenschist?
Usually, the best you can do when finding a chlorite schistose rock is to find out what the parent is. If the parent is a shale the rock is a greenschist. If basalt the rock is greenstone. If you don’t know ” greenschist” is the field term for any chloritic schistose rock.
Where are greenschist facies found?
Greenschist facies prevail in the middle levels of oceanic crust and upper levels of orogenic belts. Many supracrustal rocks in Archean terranes are metamorphosed at greenschist facies, hence the name “greenstone belts.”
What is greenschist from?
Greenschists form by metamorphism of basic igneous rocks, the chlorite component being derived from the ferromagnesium minerals present in the original rock. Chlorite imparts a green colour to the cleaved rock, hence the name ‘greenschist’.
Is greenschist soft?
It is sometimes thinly, sometimes thickly, schistose, and in some cases almost massive; and although the rock is very soft and may be readily cut, it is very tough in the more massive varieties. I will refer to greenschist as the fissile or schistose texture variety, and greenstone as the compact non-schistose variety.
What is prograde metamorphism?
Prograde metamorphism involves the change of mineral assemblages (paragenesis) with increasing temperature and (usually) pressure conditions. These are solid state dehydration reactions, and involve the loss of volatiles such as water or carbon dioxide.
Is Garnet high grade?
Chlorite, muscovite, biotite, garnet, and staurolite are index minerals representing a respective sequence of low-to-high grade rock.
Where is greenschist formed?
What do you mean by prograde?
Prograde refers to an object that spins in the same direction as its orbit. Retrograde refers to an object that spins in the opposite direction of its orbit. Earth has a prograde rotation, and asteroid Bennu has a retrograde rotation, which means the two bodies rotate in opposite directions.
What is the origin of the word serpentine?
The name comes from commonly having an abundance of green minerals such as chlorite, serpentine, and epidote, and platy minerals such as muscovite and platy serpentine.
What type of rock is greengreenschist?
Greenschist is a fine- to medium-grained foliated metamorphic rock dominated by chlorite, actinolite and epidote, with or without albite, quartz and calcite.
What is greenschist facies and how is it determined?
Greenschist facies is determined by the particular temperature and pressure conditions required to metamorphose basalt to form the typical greenschist facies minerals chlorite, actinolite, and albite.
What is the difference between blueschist and greenschist?
It isn’t always green or even a schist. Greenschist is the name of a metamorphic facies, a set of typical minerals that form under specific conditions—in this case relatively cool temperatures at high pressures. These conditions are less than those of blueschist.