Their protolith corresponds to medium- to coarse-grained pelitic sediments, which were affected by a metamorphism reaching the amphibolite facies. They show a porphyroblastic texture with granoblastic, lepidogranoblastic and poiquiloblastic matrix.
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].
The rocks of the Alutaguse zone have metamorphosed under the conditions of the amphibolite facies. In some places (Sonda-Uljaste and Haljala) the rocks show evidence of granulite facies metamorphism.
The rock samples of amphibolite facies show a clear dissimilarity in the acoustopolarigram shape from that of the rocks of prehnite-pumpellyite, greenschist and epidote-amphibolite facies.
These rocks comprise mylonitic peridotite and sub-ophiolitic metamorphic rocks that range from garnetiferous amphibolites facies to amphibolite facies to greenschist facies and un- metamorphosed sediments.
This lower amphibolite facies metamorphism overprints, in many samples, a pre-existing epidote-hornfels or greenschist assemblage containing epidote + variably sericitised plagioclase + actinolite [+ or -] biotite.