Вестник МГТУ. 2020, Т. 23, № 1.

Thus, there are three sets, and namely: R1 for the proximity of the Keivy domain rocks to the Murmansk domain rock assemblages, R2 for the proximity of the Keivy domain rocks to the Kola-Norwegian domain rocks and R 3 for the proximity of the Keivy metamorphic rocks to the supracrustal rock units of the White Sea mobile belt together with the Tersky domain rocks. The final modeling stage involves calculation of the Puri-Sen-Tamura statistics for the sets R1, R2 and R3, which allows evaluating the statistical significance of the resultant difference of the Keivy metapelites from the surrounding rocks. The below table shows proximity factors (Me( R 1 ), Me( R 2 ) and Me( R 3 )) for the composition of the studied Keivy rocks to the relevant compared objects and values of the Puri-Sen-Tamura statistics. The less the values of the given factors, the closer the compared objects. Further, the correlation was carried out consequently with the rocks of each domain surrounding the Keivy domain to evaluate the similarity of substance in any part of it with each of the domains, excluding possible influence of substance from any of the domains on the result in case of absolute predominance of the Keivy metasedimentary rocks in its lithologies. The central part of the Keivy domain, where the substance of the surrounding domains could be mixed to an ultimate degree, was dismissed from the research. Results and discussion The reconstruction of the rock composition for feeding provinces most frequently relies on the data about the composition of conglomerate pebbles and sandstone fragments. However, such geological buildups are quite exotic for the Precambrian and hardly accessible for study. This is the reason why the emplacement peculiarities of the Precambrian sedimentary rock units have long been successfully studied using data about the composition of metapelites with low permeability for post-sedimentation fluids and much better mixed and homogenized as compared to larger-grained deposits (Maslov et al., 2008;Podkovyrov et al., 2015). This paper examines their composition due to the abundance in the Keivy domain. The correlation results obtained in the course of mathematical modeling confirm the above geological and geophysical model of the Keivy domain evolution in the Early Precambrian. The results obtained during the research of the metapelite composition within various parts of the Keivy domain are not in conflict with a model earlier proposed on the basis of geological and geophysical data about the emplacement model under the conditions typical of median massifs. This, in turn, allows a somewhat different view of the issues related to the Keivy metallogeny. It is believed that the landscape of the Keivy median massif formed at the border of the Archean and Early Proterozoic corresponded to a plain locked by high mountain masses. In accordance with this research, the surface of the Keivy domain represented a shallow-water basin formed in a subequatorial zone. This assumption appears from the point that the first supercontinent (Monogea or Pangea-0) in the Earth's history took shape back then on its surface, and this could only form near the equator in accordance with the Earth's rotational mechanism (Sorokhtin et al., 2011). The chemical rock composition of the mountains encircling the Keivy domain was typical of the Archean. These are mainly tonalite-trondhjemites and granodiorites, subalkaline basaltoids, ultramafic rocks, and anorthosites. Their decomposition resulted in a series of typical sedimentary sequences rich in aluminum and potassium. These deposits accumulated in tectonically quiet and possibly warm lagoonal Neoarchean climate. Table. Comparison of metapelite compositions in respective areas of the Keivy structure with rocks of surrounding domains (see Fig. 3) Таблица. Сравнение состава метапелитов соответствующих частей Кейвской структуры с породами окружающих ее доменов (см. рис. 3) Northern part of the Keivy domain (groups 1 1 and 1 2 in Fig. 3) Southern part of the Keivy domain (groups 2 1 and 2 2 in Fig. 3) MB* 7.898** 9.432 WS+Ter 9.402 8.781 Western part of the Keivy domain (groups 1 1 and 2 1 in Fig. 3) Eastern part of the Keivy domain (groups 1 2 and 2 2 in Fig. 3) KN 7.773 10.435 Notes. * MB - Murmansk block; WS+Ter - White Sea mobile belt and Tersky domain combined into a common group of rock units framing the Keivy domain from the south; KN - Kola-Norwegian domain; ** proximity factors of the Keivy metapelites to the rocks of any geological unit. The values describing the maximum proximity of compared objects at a chosen significance level of 0.01 are put in bold. The geodynamic setting affected the Keivy median basin to accumulate an extensive sedimentary cover on its surface. The buried continental-crust rock assemblages at a high temperature gradient in the Late Archean inevitably underwent partial melting and remobilization. It is due to this process numerous alkaline granite intrusions peripherally intruded the sedimentary sequences of the Keivy domain through the weakened zones.