Вестник Кольского научного центра РАН. 2012, №1.

V.R. Vetrin, V.P. Chupin, Yu.N. Yakovlev CLASTIC MATERIAL SOURCES AND GEODYNAMIC CONDITIONS OF FORMATION OF HIGH- ALUMINA GNEISSES OF THE PECHENGA PALAEORIFTING STRUCTURE BASEMENT The basement of the Palaeoproterozoic Pechenga structure was drilled by the Kola Superdeep Borehole (SD-3) at the depths of 6842-12262 m. It consists of alternating strata of metavolcanic dacite, plagiorhytodacite rocks and high-alumina gneisses; the protoliths of these rocks corresponded mainly to graywackes. Resulting from the examination of zircons from the metaclastic rocks of the 1st, 3rd, and 9th strata of the SD-3, the detrital, anatectic, metamorphogenic, and contact-metasomatic genetic types have been identified. The detrital zircons include several age groups. The most homogeneous, i.e., comparable to zircons from tonalite gneisses (bottoms of the SD-3 section) and from surrounding rocks, zircons have appeared to be those from gneisses of the deepest 9thstratum. The data on the age of these zircons, along with a poor rounding of the grains, signifies formation of the host gneisses' protoliths owing to washing-out and redeposition of material. The widening of alimentation areas, which supplied clastic material into sedimentation basins, took place during the formation of alumina gneisses of the 3rdand especially 1st strata of the section. The analysis of a spatial arrangement and composition of magmatic rocks and metaclastic formations in section of SD-3 and its environments allows interpreting their formation in geodynamic conditions of active continental margins - in a regional zone of the terrain formed by rocks of the Kola series. Keywords: Kola Superdeep Borehole, Neoarchaean rocks, rare elements, zircons, U-Pb isotope age, clastic material sources. Yu.A. Balashov, Ye.V. Martynov ESTIMATION OF OXYGEN FUGACITY IN THE LITHOSPHERE IN ACCORDANCE WITH THE DATA FOR RARE EARTH ELEMENTS IN ZIRCONS FROM THE MANTLE ROCKS The data ranged in REE variations and Ce+4/Ce+3 and Eu+2//Eu+3 ratios in zircons from the mantle rocks of the lithosphere are shown. A directed reduction in Ce+4/Ce+3 and an increase in Eu+2/Eu+3 is observed from top towards the deepest zones of the lithosphere to reflect a transition from oxidized to reduced regimes of rock generation in the vertical sequence of the lithosphere, and to conformwith the same gradation of oxygen fugacity in the FMQ petrological buffer. The correlation between the geochemical and petrological data has been modeled to reveal independent contrasting oxygen fugacity variation trends for the upper and lower lithosphere. Keywords: mantle rocks in the lithosphere, oxygen fugacity, geochemical and petrochemical factors. T.V. Kaulina THERMOCHRONOLOGY OF ROCKS FOR RECONSTRACTION OF MOBILE BELTS DEVELOPMENT One of the promising directions in geochronology is termohronometry or termohronology - determination of temperature regime of rocks over time based on dating of minerals with different closure temperatures of isotopic systems. U-Pb, Sm-Nd and Rb-Sr dating defined thermal evolution of the eclogitic rocks and eclogites of the Yonsky region of the Belomorian mobile belt, which allowed to draw conclusions about the geodynamic conditions. Keywords: eclogites, isotopic systems, zircon, rutile, garnet, metamorphism, closure temperature. Zh.A. Fedotov PETROCHEMICAL MODEL OF THE MANTLE MAGMATISM A diagram of pyrolite melting in Mg-(Fe+Ti)-Al coordinates is plotted in accordance with referenced tentative data. This ties up the liquid composition with pressure, and pyrolite melting degree. Three ways of separating liquid from the mantle substrate are considered. These are the gravity method if the melting degree is 25%, the filter pressing mechanism efficient if the melting degree is less than 2%, and local, almost complete melting of the mantle substance. Garnet in the solid residue plays an important part, essentially affecting the composition of the mantle magmas. Keywords: Mantle generation of magma, volcanic series, primordial magma, diagram of pyrolite melting. M.I. Dubrovsky MELT SYSTEMS AS THE BASIS OF PARAGENETIC ANALYSIS OF MINERAL ASSEMBLAGES IN IGNEOUS ROCKS The drawn simplified PH 2 0 -T-projection and crystallization scheme of the q-ne-kp-fo-mo-aq system reflect the process of the magmatic rock crystallization. The rocks are compositionally marginal between the normal series and the alkaline one, and from the normative quartz group to the normative montichellite one. Keywords: melt systems, PH 2 O-T-projection, crystallization scheme. 203