Petrogeochemistry of rocks of the Ulitarechka Sequence, a new upper Archean lithostratigraphic unit in the central part of the Kola Peninsula

Fine-grained garnet amphibolites, amphibole plagioschists, biotite-amphibole, and amphibole-biotite, epidote-biotite and biotite plagiogneisses were identified during geological mapping in the Ulita River basin in the central part of the Kola Peninsula. These rocks bear evidence of volcanogenic origin and were combined into a single lithostratigraphic unit named the Ulitarechka Sequence. On the basis of the composition of rock-forming minerals, the metamorphism of amphibolites of the Ulitarechka Formation was determined as transitional between the amphibolite and granulite facies. In terms of petrography, chemistry, and mineralogy, the rocks of the Ulitarechka Formation are well correlated with the amphibolites of the upper Archean Voche-Lambina Sequence composing the base of the Lopian Tersk-Allarechensk greenstone belt. The REE distribution patterns of the Ulitarechka Sequence are similar to those of amphibolites of the Purnach and Kuksha formations of the lower part of the Paleoproterozoic Imandra-Varzuga rift structure, suggesting their derivation from a similar magmatic source. Since the boundary between the Kola and Belomorian blocks is marked by the Lopian rocks of the Tersk-Allarechensk belt, it can be shifted to the western contact of the recognized stratified rocks of the Ulitarechka Sequence.