A Change in Composition of Rocks, Mineral Phases and Trapped Gases in The Kola Super-Deep Borehole(SD-3) Section of the Archean Complex with Depth

A considerable amount of new information about the features of rocks and ore formation at various depths has been obtained due to the investigations carried out by the Geological Institute of the Kola Science Centre, USSR Academy of Sciences, and the Kola Geological Prospecting Expedition, Ministry of Geology of the USSR on core material from the Archean complex section of the SD-3 in the depth range from 6.84–12.06 km, as well as in the sections of amphibolite-gneissic strata adjacent to the Pechenga structure. The section of the SD-3 Archean complex is characterized by alternation of the strata in biotite and biotite-amphibolic gneisses and in aluminiferous gneisses subjected to them (Kozlovsky 1984). Amphibolic rocks are mostly predominant in the second and fourth strata of biotite gneisses and in the third one of aluminiferous gneisses. We have suggested a detailed classification of amphibolic rocks comprising 12 varieties, which differ in origin, age relations to other rocks in the section, peculiarities of the structure, and mineral composition (Table 1). A selective character of occurrence in the section is recognized for many of them (Fig. 1). The mineral paragenesis of these rocks indicates their generation under conditions of epidote-amphibolite and amphibolite metamorphic facies.