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Spisiak J., Dostal J., Hovorka D., Meres S., Smirnov Yu.P.
Geochemical and mineralogical patterns of Proterozoic metapicrites from the Kola Superdeep Borehole (SG-3)
Abstract. Palaeo-volcanological analysis of volcanites from the Majarvi, Pirttijarvi and Orshoaivi Fms in the SG-3 section and near-surface zone (structural boreholes IX and X) showed a considerable structural similarity of these formations. The volcanites of the formations under consideration can be considered to be homologous rocks taking into account the lateral changes in volcanite composition and in the conditions of metamorphism with depth. Petrogeochemical analysis shows that the Majarvi, Pirttijarvi and Orshoaivi volcanic Fms have different composition, volume and facial peculiarities in different tectonic blocks. The volcanites from the Majarvi Fm are similar to the surface and near-surface homologues in their chemical composition which is indicative of the isochemical nature of metamorphic processes from prehnite-pumpellyite to amphibolite facies. Abyssal samples are just slightly depleted in ferric iron. At the same time the study of Lower Jatulian volcanites from the Pirttijarvi and Orshoaivi Fms points to a great difference in composition of the abyssal rocks and their surface homologues. As compared with the surface rocks, the abyssal rocks are subject to averaging and homogenization of the composition. Volcanites from the Pirttijarvi Fm are rich in Al2O3, partly in alkali, but depleted in ferric iron and silicic acid. The volcanites from the Orshoaivi Fm show a rapid growth in subalkaline rocks (from 20 to 70 %), mainly alkaline basalts, at the cost of a great enrichment in alkalies of initial ferrobasalts which account for more than 50 % in the surface volcanites. A number of factors point to the relation between the dislocation metamorphism of volcanites from the SG-3 section and the influence zone of the deep Luchlompolo fault. Sulphide specialization of the Majarvi Fm volcanites with minor oxide content has been established and oxide specialization of volcanites from the Pirttijarvi and Orshoaivi Fms has been confirmed. Formational analysis of volcanites from the Pechenga structure and the whole Polmak-Pechenga-Varzuga greenstone belt (PVB) allowed establishing a cyclic change in rift and orogenic tectonic regimes in the course of its formation. This cyclicity contradicts the generally accepted model of its formation as a rift structure. Two full endogenic cycles about 400 Ma each have been established for the PVB: Sumian-Sariola-Jatulian (2550-2115 Ma) and Ludia-Kalevian-Vepsian (2115-1700 Ma). Divergent basic-ultrabasic volcanites of the Sumian-Sariola-Jatulian cycle are confined only to the foot section of the Majarvi Fm. As a whole, the volcanite section of this cycle is represented by convergent products of magma differentiation of the orogenic tectonic regime – medium-acid rocks from the Majarvi, Pirttijarvi and Orshoaivi Fms. By its geodynamic nature, the PVB resembles polycyclic greenstone belt within which individual structures with rather autonomous development history – those of Pechenga, Imandra, Varzuga etc. have localized.
Printed reference: Geochemical and mineralogical patterns of Proterozoic metapicrites from the Kola Superdeep Borehole (SG-3) / J. Spisiak, J. Dostal, D. Hovorka, S. Meres, Yu.P. Smirnov // Vestnik of MSTU. 2007. V. 10, No 2. P. -.
Electronic reference: Geochemical and mineralogical patterns of Proterozoic metapicrites from the Kola Superdeep Borehole (SG-3) / J. Spisiak, J. Dostal, D. Hovorka, S. Meres, Yu.P. Smirnov // Vestnik of MSTU. 2007. V. 10, No 2. P. -. URL: http://vestnik.mstu.edu.ru/v10_2_n27/articles/14_spisiak.pdf.
