Вестник МГТУ. 2019, Т. 22, № 1.

Вестник МГТУ. 2019. Т. 22, № 1. С. 36-47. DOI: 10.21443/1560-9278-2019-22-1 -36-47 The second area of the dyke magmatism is constrained by the north-eastern coast of the Kandalaksha Bay. Nowadays, more than 300 dykes are known here. Most of them are oriented north-eastwards and compose a series of subparallel bodies with a distance between them ranging from 20-50 m to 500-700 m. Almost all of the dykes are alkaline-ultrabasic. The study of age characteristics of the intrusive magmatism allowed defining two age intervals of its activity. Early intrusive bodies, explosion pipes and dykes intruded in the period of 480-400 Ma ago. They form a north-westwards elongated zone stretching along the coast of the Kandalaksha Bay and further, including the Kovdor massif. Later magmatic events were 400-320 Ma ago. They are confined to fracturing of the north­ eastern and northern strike. The defined pattern indicates a younger age of origination of the meridional and diagonal (north-eastern) fault systems. We have analyzed spatial-temporal settings of magmatic formations in the eastern Baltic Shield and revealed that they were regularly located close to intersection nodes of major fractures in all of the four directions (Fig. 1). In general, there are 16 major nodes within the described region with intense magmatism in 10 of them. The rest 6 areas are in the north-western and eastern parts of the Kola Peninsula and on the Rybachy Peninsula. These areas have no evidence of magmatism yet, being either closed or poorly studied. Noteworthy, as a result of the research made by the authors in 1997 on the eastern Kola Peninsula (the Pulonga - Babya Rivers), a number of melilitite and kimberlite dykes have been discovered on the Kola coast of the White Sea Throat. These dyke formations have a peculiar spider-like shape with the isometrically isolated matter in the centre and 4-6-ray radiating dykes. The diameter of central bodies ranges from 2 to 8 m, apophyses are as long as 30-80 m. Dyke bodies break the Archaean crystalline basement; they are not metamorphosed and often have peculiar diagonal primary fractures formed under the magma crystallization. By the present day, these formations are poorly studied, but preliminary data indicate their Paleozoic age. As a result of the Caledonian-Hercynian activity in the Baltic Shield, several magmatic complexes intruded and formed on the shoulders of these structures, in rift areas and intersection nodes of the largest lineaments (Fig. 3). Consequently, the Paleozoic alkaline-ultrabasic, melilitite and kimberlite magmatic province was formed within the Baltic Shield and northern Russian Platform. 0 100 200 km Barents Sea Fig. 3. Scheme of tectonics and distribution of major intrusive massifs and Paleozoic explosion pipes in the north-eastern Baltic Shield: 1 - linear areas of localized Paleozoic deep tectonic faults; 2 - alkaline-ultrabasic intrusions; 3 - melilitite explosion dykes; 4 - kimberlite explosion pipes; 5 - lamproite explosion pipes Рис. 3. Схема проявления тектоники и распределения основных интрузивных массивов и трубок взрыва палеозойского возраста в северо-восточной части Балтийского щита: 1 - линейные зоны концентрации глубинных тектонических разломов палеозойского возраста; 2 - интрузии щелочно-ультраосновного состава; 3 - мелилититовые трубки взрыва; 4 - кимберлитовые трубки взрыва; 5 - лампроитовые трубки взрыва 39