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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The second one corresponds to greenschist facies (Figure 30, represented by chlorite + muscovite + epidotesr-plagioclase (albite) + quartz + actinolite.
This mineral association is typical of greenschist facies (Figure 3h and 3i).
Then, a progressive metamorphism in these rocks is marked by the passing of greenschist facies mineralogy [actinolite + chlorite + quartz + plagioclase (albite) + epidote minerals [+ or -] muscovite [+ or -] calcite] to epidote-amphibolite facies mineralogy [hornblende + epidote minerals + quartz + albite [+ or -] garnet], and finally to amphibolite facies mineralogy [hornblende + garnet + plagioclase [+ or -] quartz].
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.
2), whereas low-grade metamorphism is broadly equivalent to the greenschist facies (e.
P-T trajectories that pass below the invariant point) most mafic rocks show a progression from zeolite to prehnite-actinolite to greenschist facies (Figs.
It was metamorphosed only to lower greenschist facies, possibly in the same event that retrograded the Seven Hundred Acre Island Formation.
The sedimentary protoliths of the Islesboro Formation have been metamorphosed to lower greenschist facies.
Mafic dikes, as well as a few dacite dikes also metamorphosed to lower greenschist facies, occur locally.
Like their host rocks, the sills show evidence for greenschist facies metamorphism, as indicated by the mineral assemblage chlorite, actinolite, epidote, and albitic plagioclase.
The country rock these veins crosscut is mostly basalt and andesite flows metamorphosed to lower greenschist facies and locally containing approximately 1% pyrite.