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Vol. 10 (2007 year), No. 2

Turkina O.M., Vetrin V.R.
Isotopic-geochemical systematization and geodynamic setting of formation of the Late Archaean tonalite-trondhjemite complexes in the Kola Superdeep Borehole section and Pechenga structure framing

The Proterozoic Pechenga complex penetrated by the Kola superdeep borehole SG-3 (0-6840 m) represents a rhythmic alternation of volcano-sedimentary formations with co-magmatic bodies of gabbro-wehrlites and intrusions of gabbro-diabases and dacite-andesite porphyries. We have studied bodies of metapicrite rocks from the Nikelska group – the Matert and Zhdanov Formations. Metapicrites are medium-grained rocks with variable alteration, some of them metamorphosed at the greenschists facies. In the studied rocks olivines were totally altered. Clinopyroxenes correspond to augite, rarely to hedenbergite. Amphiboles occur in several generations, the first kaersutites co-exist with clinopyroxenes. Amphiboles around clinopyroxenes correspond to edenite and the amphiboles which originated during the metamorphosis under the greenschist facies PT conditions correspond to actinolites, ferroactinolites and tremolites. We compared metapicrites from SG-3 and ferropicrites on the surface. They are geochemically very similar. The studied Proterozoic metapicrites from the Matert and Zdhanov Formations have a range of SiO2 between 38.69 and 48.2 wt%. The MgO content varies from 10.53 to 33.94 wt%, the Al2O3 content varies from 2.64 to 11.28 wt%, the TiO2 content varies from 1.25 to 4.18 wt% and CaO content varies from 1.14 to 13.99 wt%. The Fe2O3 content varies from 16.06 to 20.73 wt%, Mg# from 50.16 to 77.29 wt% and LOI from 3.90 to 10.30 wt%. High concentrations of compatible elements Ni, Co, Cr in metapicrites from the Matert and Zhdanov Proterozoic Formations indicate a mantle source. REE-chondrite normalized patterns of these rocks are different from the MORB basalts pattern, they are enriched in LREE. The concentrations of most HFSE and REE are considered to reflect the primary magmatic distribution and correspond to E-type MORB and tholeiitic WPB.

(in Russian, стр.11, fig. 7, tables. 3, ref 44, Adobe PDF, Adobe PDF 0 Kb)