Вестник МГТУ. 2020, Т. 23, № 1.

Introduction The Keivy domain occupies the northeastern part of the Baltic Shield and borders with the Kola-Norwegian domain in the east and west and with the Murmansk domain in the north. In the south, it is constrained by the Early-Proterozoic rocks of the Pechenga-Imandra-Varzuga-Ust-Ponoy greenstone belt (Fig. 1). The Keivy domain typically includes a proveniance of Archean igneous continental-crust rocks, which are tectonically confined to the Keivy domain overlain by a volcano-sedimentary cover in its southwestern part. This structural unit may be considered as a special domain of the Kola Precambrian deep-seated collision structure (Митрофанов и др., 1997). Fig. 1. Schematic zoning of Early Precambrian geostructural elements in the Earth’s crust of the northeastern Baltic Shield (Козлов и др., 2019). Crustal domains: 1 - Murmansk; 2 - Kola-Norwegian; 3 - Lotta; 4 - Keivy; 4a - Verkhneponoysky; 5 - Eastern Kola; 6 - Chapoma; 7 - Tersky. Greenstone and granulite belts: 8-10 - Archean: 8 - Lapland-Kolvitsa; 9 - Titovka-Kolmozero (Kolmozero-Voronya); 10 - Sergozersky-Strelninsky; 11, 12 - Neoproterozoic: 11 - Pechenga-Imandra-Varzuga-Ustponoysky; 12 - Northern-Karelian; 13 - Riphean rift and continental marginal sediments Рис. 1. Схема районирования раннедокембрийских геоструктурных элементов земной коры северо-восточной части Балтийского щита (Козлов и др., 2019). Домены коры: 1 - Мурманский; 2 - Кольско-Норвежский; 3 - Лоттинский; 4 - Кейвский; 4а - Верхнепонойский; 5 - Восточно-Кольский; 6 - Чапомский; 7 - Терский. Зеленокаменные и гранулитовые пояса: 8-10 - архейские: 8 - Лапландско- Колвицкий; 9 - Титовско-Колмозерский (Колмозеро-Воронья); 10 - Сергозерско-Стрельнинский; 11, 12 - неопротерозойские: 11 - Печенга-Имандра-Варзуга-Устьпонойский; 12 - Северо-Карельский; 13 - рифтогенные и окраинно-континентальные отложения рифейского возраста The supracrustal units of the Keivy domain are described in (Бельков, 1963; Геология..., 2002). The rocks are mainly represented by biotite and amphibole gneisses, two-pyroxene crystalline schists and garnet- biotite gneisses. The intrusive unit is composed of gabbro-anorthosites, potassium and alkaline granites. The U-Pb age of zircons from the metamosphosed rhyodacites of the Lebyazhinskaya Suite is 2,871±15 Ma (Беляев и др., 2001). The researchers of the Keivy domain have examined possible reasons for the peculiarities of the composing rock assemblages. One of the reasons includes regional metasomatic processes genetically related to the alkaline granite bodies (Козлов и др., 2017). Their age is reliably determined to be 2,751±41 Ma ( Позднеархейский..., 2001). The studied compositional features at the bottom of the Keivy mafic metamorphic volcanic rocks suggest that their protoliths could be the most ancient formations within the Kola Peninsula (Kozlov et al., 2018). A detailed geological and petrogeochemical study of the Keivy metamorphic rocks allowed the authors to demonstrate earlier that it could be considered as a special domain located within the Kola Precambrian deep- seated collision structure. However, no preferred affinity of the Keivy rocks to any geodynamic structural (granite-greenstone or granulite-gneiss) type has been identified. It shall also be noted that the evolutional nature of the Archean stage in the development of the Keivy domain significantly differs from all the adjacent continental-crust formations in the eastern part of the Baltic Shield. The cover-type volcano-sedimentary rocks are the earliest within the Keivy domain. The available data indicate their near-constant accumulation in the internal domain areas during cratonization. The border interaction of the Keivy domain and other circumfluent continental-crust rocks is underexplored. No Late Archean metamorphism has been found within it although traces of collision with other domains should have resulted in a peripheral low-gradient contact metamorphism.