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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. Greenschist facies results from low temperature, moderate pressure metamorphism.
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:
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] Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface ...
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]
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 ...
Pressure-temperature conditions have been estimated to be 5-7 kbar and 555-655 °C for the amphibolite-facies metamorphism in the area. [12] Due to the presence of the coeval arc-related granodiorites in the same region, the elevated P-T conditions may be due to a back-arc intra-continental rift setting with elevated heat flow.
Width of the peak at one half of its height is measured and this angle (recorded with units of ∆ °2θ), [1] can be plotted on a chart with metamorphic zones and facies like the one in figure 1. If the illite crystallinity values fall in the 0-0.25 °2θ range, it corresponds with a metamorphic epizone or greenschist facies.
Most likely, fluids have been produced under prograde greenschist- to amphibolite-facies metamorphism (220–450 °C and 1–5 Kbar). [3] The generally low salinity of the hydrothermal fluids can be attributed to devolatilization of minerals associated with metamorphic phase reactions, involving dehydration and decarbonisation. [ 26 ]