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Vol. 20 (2017 year), No. 1, DOI: 10.21443/1560-9278-2017-20-1/1

Kozlov N. E., Fomina E. N., Martynov E. V., Sorokhtin N. O., Marchuk T. S.
On reasons of specific composition of the Keivy domain rocks (the Kola Peninsula)

The Keivy domain differs from the other structures of the Kola region by the specific composition of the metamorphic complexes, the presence of the oldest for the region alkaline granites and gabbroanorthosites associated with them as well as by the presence of unique mineral deposits. The previous studies of the Keivy structure showed that within this structure there are metasedimentary formations that differ from both Early Precambrian metasedimentary rock associations of the Kola region and Phanerozoic sedimentary complexes in the content of titanium and the ratio Al2O3/SiO2. The present study confirms the correctness of this conclusion. The authors have attempted the search of the generalized indicator (trend) describing the nature of changes in the chemical composition of rocks in the transition from Low-Ti to High-Ti varieties of rocks (with simultaneous increase in the ratio Al2O3/SiO2). To solve this problem the method of search of differences in the specified number of sets has been used with the partial order relation introduced by the researcher. The formations of the same type and age, namely metapelites of the Chervurtskaya suite of the Keivy series, have been chosen as the informational basis. Such indicator has been found. It describes the process which besides a significant titanium input was accompanied by a simultaneous increase in the content of CaO and decrease in the content of Al2O3, ?Fe, and Na2O. It must be emphasized that the obtained trend is not related to the supergene processes characterized by the similar behavior of titanium with aluminum and iron which is especially clearly exhibited in the formation of crusts of weathering. The location on this generalized indicator of the points of rock compositions of all strata of the geological section of the Keivy domain taken far or close to alkaline granites corresponds to the position of less or more titaniferous rocks, thus confirming the assumption of a metasomatic alteration of the latter. The fact that all the metasedimentary Keivy formations are subjected to metasomatic alteration most probably related to the Archean complexes of alkaline granites, which is confirmed by direct geological observations of the relationships of the Lebyazhinskiye and Chervurtskiye rock complexes with alkaline granites, allows us to speak about their Archean age.

(in Russian, стр.12, fig. 4, tables. 1, ref 29, Adobe PDF, Adobe PDF 0 Kb)

Vol. 23 (2020 year), No. 1, DOI: 10.21443/1560-9278-2020-23-1

Kozlov N. Е. , Sorokhtin N. О., Martynov E. V., Marchuk T. S.
Geodynamics and metallogeny of the Keivy domain (Baltic Shield)

Geodynamic and petrogeochemical study of the Keivy domain in the Baltic Shield has shown that it was overlapped by surrounding microcontinents in the Archean. As a result, the Baltic Shield was subject to cratonization. Thus, the Keivy microcontinent can be considered as the most ancient known median massif of the continental crust. Specific features of its geodynamic evolution predetermined conditions for formation of unique in scale stratiform deposits of alumina raw materials on the surface of the microcontinent. The paper describes and justifies the mechanism of alumina formation by physical-chemical decomposition of Archean and early Proterozoic metamorphosed sedimentary complexes in the Kola region of the Baltic Shield. Besides, the study of metallogenic features of transformation processes in the Archean continental crust of the Keivy microcontinent and its rimming suggests that carbonaceous schists of the Keivy domain that formed in the sedimentary cover can be significantly rich in nanogold. It will allow considering the central part of the Kola region as a major gold-bearing province. The authors believe that the metallogenic forecast based on geodynamic reconstructions is promising for further research of early Precambrian complexes. This work continues a series of publications on structural-material study of the Keivy domain

(in English, стр.7, fig. 4, tables. 1, ref 14, AdobePDF, AdobePDF 0 Kb)

Vol. 24 (2021 year), No. 1, DOI: 10.21443/1560-9278-2021-24-1

Kozlov N. Е., Sorokhtin N. О., Martynov E. V., Marchuk T. S.
Peculiar features of the supracomplexes formation in the Keivy domain

The Keivy domain (the northeastern part of the Arctic zone of the Fennoscandian Shield) during the period of the maximum manifestation of the Late Archean collisional processes was overlapped by tectonic allochthons of adjacent microcontinents thrust over it, submerged relative to other blocks of the continental crust, and acquired the features of a classical middle massif. In the process of studies that allow a detailed description of the formation of the supracrustal complexes of the Keivy structure, it has been found that the formation processes of the Kola orogeny had a pronounced spatial and temporal zoning and impulsive character. The maximum degree of orogeny was experienced by the rock associations of the Murmansk domain, as a result of which terrigenous material transported from its mountain slopes prevailed in the metasedimentary complexes of the Keivy domain throughout the entire period of their formation. The substance removed from the Murmansk domain was more actively accumulated in the metasedimentary rocks of the Lebyazhinsky suite; then a regular attenuation was observed within all domains, but at the last stage of the formation of the section of the Keivy sedimentary strata, the structural-material complexes of the Murmansk domain again begin to degrade more actively. A detailed study of the compositional features of the supracrustal complexes of the Keivy structure refutes the currently emerging point of view on the coeval formation of alkaline granites and felsic metavolcanics of the Lebyazhinsky suite. It can be argued with a high degree of probability that the rocks used to draw this conclusion (for which the age of 2.678 ± 7 Ma) is not typical of the supracrustal section of the metavolcanics of the Lebyazhinsky suite and are metasomatites.

(in Russian, стр.10, fig. 3, tables. 1, ref 26, AdobePDF, AdobePDF 0 Kb)