What are the metamorphic zones grades?
When mapping the metamorphic grade of a terrane, a geologist has to take the lithology of the rock in account. Lithologies are mainly dependent on the protolith, the original rock before metamorphism. The main lithologies are ultramafic, mafic, felsic (or quartzo-feldspathic), pelitic and calcareous.
What are pelitic rocks?
A pelite (Greek: pelos, “clay”) or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone.
What are the facies of regional metamorphism?
The facies associated with regional metamorphism include, at low grade, the zeolite and prehnite-pumpellyite facies. In areas belonging to high-pressure facies series, the rocks are predominantly in the blueschist and eclogite facies.
How do you identify metamorphic facies?
Metamorphic facies is not obvious in a given field specimen. To sum up, a metamorphic facies is the set of minerals found in a rock of a given composition. That mineral suite is taken as a sign of the pressure and temperature that made it. Here are the typical minerals in rocks that are derived from sediments.
What are index minerals and metamorphic facies?
When an index mineral is found in a metamorphosed rock, it indicates the minimum pressure and temperature the protolith must have achieved in order for that mineral to form. The higher the pressure and temperature in which the rock formed, the higher the grade of the rock.
What is metamorphic facies in geology?
In current usage, a metamorphic facies is a set of metamorphic mineral assemblages, repeatedly associated in space and time, such that there is a constant and therefore predictable relation between mineral composition and chemical composition. The facies concept is more or less observation-based.
Is gneiss a pelitic?
Pelitic schists or pelitic gneisses are derived by metamorphism of argillaceous or fine-grained aluminous sediments. The pelitic protolith is generally very fine-grained. During metamorphic overprint there is only a slight coarsening of the mineral grains in the corresponding like-grained metamorphic product.
What are the 7 types of regional metamorphism?
Contact Facies Series (very low-P); Buchan or Abukuma Facies Series (low-P regional) ; Barrovian Facies Series (medium-P regional); Sanbagawa Facies Series (high-P, moderate-T); Franciscan Facies Series (high-P, low T).
What are the 5 types of regional metamorphism?
According to the composition type, metamorphic rock can be also divided into five series: (1) mudstone series (slate, phyllite, mica schist, biotite gneiss), (2) felsic series (quartzite, plagioclase gneiss, leptynite, and leucoleptite), (3) carbonate rock series (calcium and magnesium metamorphic rock series, such as …
Is eclogite a metamorphic facies?
It is a rock type that gave name to a metamorphic facies. Eclogite facies is characterized by pressures in excess of 1.2 GPa (45 km depth) and temperature exceeding at least 400-500 °C. 400-500 degrees at 45 km depth is below the crustal average (25 °C per kilometer of depth).
Is staurolite a metamorphic facies?
The chlorite and biotite zones represent greenschist facies metamorphism, and the garnet, staurolite, kyanite, and sillimanite zones represent amphibolite facies metamorphism.
What are metamorphic facies?
This pressure and temperature environment is referred to as Metamorphic Facies. (This is similar to the concept of sedimentary facies, in that a sedimentary facies is also a set of environmental conditions present during deposition).
Why are metamorphic pelites hornfelsic?
Contact metamorphism of pelites typically leads to the index minerals this order of appearance is strongly dependent on pressure and bulk-rock composition. Such rocks often lack foliations and so are hornfelsic.
What is metamorphism of pelitic (Al-rich) rocks?
Preprint of Palin and Dyck (2020) ‘ Metamorphism of Pelitic (Al-rich) rocks. Encyclopedia of including lakes, the distal portions of continental shelves, and deep-sea abyssal plains. When highly sensitive to changing pressure and temperature conditions within the Earth. As such, tectonic evolution of geological terranes.
What is the Order of metamorphism of pelites?
Contact metamorphism of pelites typically leads to the index minerals this order of appearance is strongly dependent on pressure and bulk-rock composition. Such rocks often lack foliations and so are hornfelsic. Metamorphism due to burial in a collisional specific compositional variation may alter this sequence. At upper amphibolite- and melt.