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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.
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. [1] The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram in Figure 1). [1]
It initially undergoes low-grade metamorphism to metabasalt of the zeolite and prehnite-pumpellyite facies, but as the basalt subducts to greater depths, it is metamorphosed to the blueschist facies and then the eclogite facies. Metamorphism to the eclogite facies releases a great deal of water vapor from the rock, which drives volcanism in the ...
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]
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]
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.
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]
Based on inspection of extreme metamorphism and post-subduction magmatism at convergent plate margins, paired metamorphic belts are further extended to two contrasting metamorphic facies series: [7] one is blueschist to eclogite facies series that was produced by subducting metamorphism at low thermal gradients of <10 °C/km, and the other is ...