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Chlorite schist, a type of greenschist Greenschist (prasinite) at Cap Corse in Corsica, France Greenschist (epidote) from Itogon, Benguet, Philippines. Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically 300–450 °C (570–840 °F) and 2–10 kilobars (29,000–145,000 psi). [1]
The zeolite facies is the metamorphic facies with the lowest metamorphic grade. At lower temperature and pressure processes in the rock are called diagenesis. The facies is named for zeolites, strongly hydrated tectosilicates. It can have the following mineral assemblages: In meta-igneous rocks and greywackes:
In his pioneering work on metamorphic facies in the Scottish Highlands, G.M. Barrow identified the chlorite zone as the zone of mildest metamorphism. [12] In modern petrology, chlorite is the diagnostic mineral of the greenschist facies. [10] This facies is characterized by temperatures near 450 °C (840 °F) and pressures near 5 kbar. [13]
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 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. [1]
Petrogenetic grid for metapelites (click to zoom). [1] [2] Each line represents a metamorphic reaction.Metamorphic facies included are: BS = Blueschist facies, EC = Eclogite facies, PP = Prehnite-Pumpellyite facies, GS = Greenschist facies, EA = Epidote-Amphibolite facies, AM = Amphibolite facies, GRA = Granulite facies, UHT = Ultra-High Temperature facies, HAE = Hornfels-Albite-Epidote facies ...
This reaction takes place in nature when a mafic rock goes from amphibolite facies to greenschist facies. A metamorphic reaction is a chemical reaction that takes place during the geological process of metamorphism wherein one assemblage of minerals is transformed into a second assemblage which is stable under the new temperature/pressure ...
Examples include metamorphic overprinting (superimposed metamorphism [1]), in which new structure, [2] texture, or mineral composition is imposed on existing rock. [3] [4] For example, the Tauern window of Alps contains beds that were originally metamorphosed to eclogite but have since been overprinted to the blueschist and then the greenschist ...
Prograde metamorphism to either greenschist facies or amphibolite facies tends to revert igneous olivine to metamorphic olivine, serpentinite or talc carbonated ultramafic schists. In the ore environment, the metamorphism tends to remobilise the nickel sulfide which, during peak metamorphism, has the yield strength and behaviour of toothpaste ...