Rocks of prehnite-pumpellyite, greenschist and
epidote-amphibolite facies occurring at depths of 9-6000 m in the Kola superdeep borehole section have a common origin and, in general, they do not differ much from the rocks selected at the outcrops elsewhere in the Pechenga complex (Glebovitsky, 1973; Petrov, 1999; Gorbatsevich and Trishina, 2017).
The rocks of the CVG are highly tectonized and metamorphosed to mainly greenschist and
epidote-amphibolite facies and have the development of altered/sheared zones along local faults within these rocks.
The first one corresponds to epidote-amphibolite facies, represented by hornblende + epidote group minerals + quartz + albite [+ or -] garnet (Figure 3c).
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].
This is supportd by the mineralogy of greenschist facies that is found among the mineral assemblages of the amphibolite and epidote-amphibolite facies, such as chlorite + actinolite + epidote minerals + quartz (mineralogy of greenschist facies), between hornblende + epidote minerals + quartz + albite [+ or -] garnet (mineralogy of epidote-amphibolite facies) in the hornblende schists (Figures 4d), and the chlorite + muscovite + epidote minerals + plagioclase (albite) + quartz (mineralogy of greenschist facies) between the hornblende + garnet + plagioclase [+ or -] quartz (amphibolite facies) in the garnet amphibolites (Figure 3f).
One mafic volcanic breccia block, sampled in the northeastern part of the melange yields evidence for lower
epidote-amphibolite facies metamorphism prior to emplacement in the melange.
Rocks of basaltic composition are represented by schistose amphibolites metamorphosed at epidote-amphibolite facies at T = 420-470 [degrees]C and p = 4.9-5.4 kbar (Petrov, 1999).
Six samples of epidote-amphibolite facies were collected at the Valasjoki site, Figure.
9) for the samples of epidote-amphibolite facies indicates a more pronounced presence of elastic anisotropy of rocks and significant structural heterogeneity.
The basement comprises deformed and epidote-amphibolite facies metamorphosed rocks ranging from mafic to granodioritic composition.
During the collision it may have experienced deformation and metamorphism in epidote-amphibolite facies. During the Late Proterozoic, the terrane played host to continental magmatism related to epeirogenic uplift (doming) and extension.