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Vol. 1 (1998 year), No. 3

Vetrin V.P., Ovchinnikova G.V., Neimark L.A., Gorokhovsky B.M., Smirnov Yu.P.
Muscovite-Microcline Metasomatites in Rocks of the Archaean Complex of the Kola Superdeep Borehole: Stages of Formation and Sources of Substance

Muscovite-microcline metasomatites on gneisses of the Archaean complex of the Kola superdeep borehole are found out in the bottom part of the section on the depth 12172-12235 m and by the geological position, structure and age are correlated with garnet-like rocks of the metasomatite formation occupying the area not less than 300 km² in the Archaean rocks of the Pechenga riftogenic structure's northern frame. The metasomatite formation occured in conditions of increased potential of CO₂, P, F, B and was accompanied by increase in gneisses of the content substratum as elements of siderophile (Fe, Ti, Cu, Ni, Co, Cr, V), and litophile (K, Rb, Ba, Nb, Zr, Y, TR, Pb, Th) group as well. These features of the structure are peculiar for subalkaline rocks of the early-orogenic trachybasaltic formation, which rocks have mantle origin and, as it is supposed, were a source of fluids rich of carbonic acid. On the Pb-isotope data, lead in the metasomatites was formed by mixing of mantle lead introduced by fluids with lead from gneiss substratum with age 2.8 Ga. The more radiogenic isotope structure of Pb of some plagioclases adequate to lead of upper crust formations, does not contradict the assumption of reworking of Pb-Pb systems of feldspars from muscovite-microcline metasomatites during intrusion of anatectic bodies of the Svecofennian granites.

(in Russian, стр.8, fig. 4, tables. 2, ref 13, MS Word 95, MS Word 95 204 Kb)