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Greenschist facies results from low temperature, moderate pressure metamorphism. Metamorphic conditions which create typical greenschist facies assemblages are called the Barrovian Facies Sequence, and the lower-pressure Abukuma Facies Series. Temperatures of approximately 400 to 500 °C (750 to 930 °F) and depths of about 8 to 50 kilometres ...
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 ...
The alteration occurs during either late-stages of magmatic crystallization at low temperatures (< 500 °C) or during low-grade metamorphic events (sub-greenschist facies metamorphism). The reaction is paramorphic, meaning that the structure of the mineral is modified, but its original chemistry is retained. [2]
In the Pelagon, rocks have Barrovian-type regional metamorphism up to greenschist grade on the sequence of metamorphic facies. In the Serbo-Macedonian Massif, rocks also reach greenschist facies and exhibit Barrovian-type metamorphism. [5]
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 ...