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Vol. 1 (1998 year), No. 3

Balagansky V.V., Timmerman M.Ya., Kislitsyn R.V., Dayly J.S., Balashov Yu.A., Gannibal L.F., Sherstenikova O.G., Ryunenen G.I.
The Isotope Age of the Kolvitsa Belt and the Umba Granulite Terrane (South-East of the Lapland Granulite Belt), the Kola Peninsula

The Lapland Granulite Belt (LGB) in the northern Baltic Shield is interpreted to have resulted from plate tectonic processes in the Palaeoproterozoic. The Kolvitsa Belt and the tectonically overlying metasedimentary Umba Granulite Terrane (UGT) are thought to be isolated fragments of the LGB in the Kola Peninsula. U-Pb (on zircon) and Rb-Sr (whole rock) ages, as well as Sm-Nd and Rb-Sr data presented in the paper indicate that the Kandalaksha metabasalt sequence, the Por’ya Guba mafic to intermediate granulite complex, the Kolvitsa massif of gabbro-anorthosites and its dyke complex are related to a single volcano-plutonic suite, which was developing 2.43-2.47 Ga ago at an initial stage of the earliest Palaeoproterozoic rifting of a Neoarchaean craton. Values of initial 143Nd/144Nd and 87Sr/86Sr ratios in rocks of this Kolvitsa suite coincide with those of 2.44-2.50 Ga old layered mafic intrusions in the Baltic Shield. In contrast with the Kolvitsa suite, the deposition of sedimentary protoliths of garnet-quartz-feldspar granulites and garnet, sillimanite and cordierite gneisses of the UGT was occurring ca. 2.0-2.1 Ga ago as suggested by model depleted mantle ages of 2.1-2.4 Ga and age data available on the granulite metamorphism (1.91 Ga). The sedimentary protoliths of the Umba paragranulites were derived largely from Palaeoproterozoic juvenile material, which permits to interprete the depositional environment as an island arc setting.

(in Russian, стр.14, fig. 5, tables. 3, ref 44, MS Word 95, MS Word 95 1420 Kb)

Vol. 15 (2012 year), No. 2

Balashov Yu.A., Martynov E.V.
Correlation of oxygen fugacity in the mantle lithosphere between Ce+4/Ce+3 relation of zircons and petrological buffer FMQ

The paper presents variations of Ce+4/Ce+3 and Eu+3/Eu+2 in zircons from different mantle rocks of the lithosphere. The ratio Ce+4/Ce+3 reflects the "oxidation" degree of the zircon (and rock) formation and Eu+3/Eu+2 – "reducing" properties of the source which allows one to control the level of the oxygen fugacity. A correlation of the ratio Ce+4/Ce+3 in zircons ("geochemical buffer" – "CeB") and petrological buffer FMQ of rocks in the lithosphere vertical section has been performed. This allows one to determine the boundaries of the "upper" and "lower" parts of the lithosphere and reveal the similarity of the variation range of the oxygen fugacity in the upper lithosphere and analogous parameters of the crustal rocks of different age. Besides it helps to establish unique reducing parameters for oxygen in the foot part of the lithosphere.

(in English, стр.19, fig. 13, tables. 4, ref 50, Adobe PDF, Adobe PDF 0 Kb)