greenschist facies


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Related to greenschist facies: Metabasites

greenschist facies

[′grēn‚shist ′fā·shēz]
(petrology)
Any schistose rock containing an abundance of green minerals and produced under conditions of low to intermediate temperatures (300-500°C) and low to moderate hydrostatic pressures (3000-8000 bars).
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Rocks of greenschist facies have been studied in the area of Lake Tulijavr and middle reaches of the River Shuonijoki located, respectively, in the south-eastern and western parts of the Pechenga structure.
This is based on the following evidences: Field relations between the different lithotypes of metabasites reflect the occurrence of a prograde metamorphism, which is manifested by an increase of metamorphism from the greenschist facies (chlorite and actinolite schists with or without garnet, and metabasalts) to the amphibolite facies (amphibolites with or without garnet).
Their protolith corresponds to fine-grained pelitic sediments, which were affected by a metamorphism reaching the greenschist facies. They show a lepidoblastic to granolepidoblastic textures, which are defined by the alignment of muscovite.
The second one shows the greenschist facies, represented by chlorite + actinolite + epidotes + quartz (Figure 3d).
The majority of the schist identified was of the chlorite zone of the greenschist facies, although some glaucophanic greenschists and schists of the prehnite-pumpellyite facies also occur.
(1996) noted that the grade of metamorphism is very low to low (lower greenschist facies at most), with localized higher grade areas related to contact metamorphism by late Neoproterozoic and Devonian plutons.
The Deosai volcanics are the porphyritic rocks showing mild to severe alteration while the meta-volcanics of Burji-La Formation are metamorphosed to greenschist facies. The Deosai volcanics also have suldes-bearing mineralized altered zone where the chalcopyrite and pyrite are well observed.
The supracrustal rocks are generally metamorphosed to amphibolite facies, less commonly to granulite facies, and rarely to greenschist facies. Many of these rocks partly retain their primary structures and textures despite the intense deformation and metamorphic overprints in almost all supracrustal belts.
Regional metamorphism in this area reached prehnite-pumpellyite to lower greenschist facies conditions (Boone et al.
The sequence was intensely folded, and metamorphosed to greenschist facies, locally to amphibolite facies, during the Upper Permian and Lower Triassic.
These are strongly deformed highly tectonized and are metamorphosed mainly to greenschist facies and lesser extent to epidote-amphibolite facies.
It was initially metamorphosed to lower amphibolite facies and was later retrograded to lower greenschist facies. The lower amphibolite facies metamorphism is Neoproterozoic (670 to 650 Ma) as inferred from the [[blank].sup.40]Ar/[[blank].sup.39]Ar high temperature release spectra of homblende separates.