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Yakovlev Yu.N., Skuf'in P.K., Bayanova T.B.
The rhyodacitic porphyry body in the section of the SG-3 Pechenga area (age and ore mineralization)
Abstract. By geological, geophysical, petrological and isotopic-geochronological data the Archaean complex in the SG-3 section correlates with amphibolite-gneiss complexes of the granite-greenstone area of the Svanvik-Neiden segment located in the Kola-Norwegian block. Plagiogneisses of tonalite-trondhjemite composition, being one of the major components of the SG-3 Archaean complex and the borehole surroundings, include two types. Plagiogneisses of type A are depleted in heavy lanthanoids to a different degree and their ?Nd ranges from +2 to +0.5. Plagiogneisses of type B are rich in HREE, incompatible trace elements and are characterized by negative ?Nd values which is evidence of contamination of the primary melt by the ancient crust material. Amphibolites associated with plagiogneisses are close to tholeiitic basalts of modern oceanic plateaus and Archaean greenstone belts in the trace element composition. By the experimental data, tonalite-trondhjemite melts corresponding to plagiogneisses of types A and B and depleted in heavy lanthanoids to a different degree, formed during metabasic rocks melting at Р ? 10-15 and ? 8 kbar respectively. Model metabasite sources of tonalite-trondhjemite melts that are initial for plagiogneisses of type A are comparable with basalts of modern oceanic plateaus and Archaean basalts of plume origin in the trace element patterns and their indicator ratios. Low Mg# of plagiogneisses excludes the contribution of mantle peridotites in their formation and, hence, does not correlate with subduction oceanic plate. Variations of trace element and isotopic composition of plagiogneisses more likely point to formation of tonalite-trondhjemite melts at different levels of the thickened mafic crust which includes metabasalt material that is heterogeneous in trace element and isotopic composition. The composition peculiarities of amphibolites and model metabasite sources of tonalite-trondhjemite melts suggest that formation of the thickened crust might be caused by accretion of oceanic plateaus.
Printed reference: Yakovlev Yu.N., Skuf'in P.K., Bayanova T.B. The rhyodacitic porphyry body in the section of the SG-3 Pechenga area (age and ore mineralization) // Vestnik of MSTU. 2007. V. 10, No 2. P. -.
Electronic reference: Yakovlev Yu.N., Skuf'in P.K., Bayanova T.B. The rhyodacitic porphyry body in the section of the SG-3 Pechenga area (age and ore mineralization) // Vestnik of MSTU. 2007. V. 10, No 2. P. -. URL: http://vestnik.mstu.edu.ru/v10_2_n27/articles/16_Yakov.pdf.
