Volume 29, 5, 2010 |
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A.I. Khanchuk.
Integration program " Structure and formation of major types ogf
geologic structures of mobile belts and platforms" of Earth Sciences
Department, RAS, Far East Branch, RAS, Siberian Branch, RAS, and
Urals Branch, RAS. 3 A.I. Malinovsky, M.I. Tuchkova. Lithochemistry of paleoisland arc complexes as a criterion of their recognition in the paleobasins of the Russian Far East orogenic belts 5 A.V. Maslov, A.D. Nozhkin, V.N. Podkovyrov, E.F. Letnikova, N.V. Dmitrieva, Yu.L. Ronkin. Trace elements abundance ratios of Riphean fine-grained terrigenous rocks of the Uchur-Maya region and Yenisei ridge 23 A.N. Didenko, V.A. Guryanov, A.Yu. Peskov, A.N. Perestoronin, D.V. Avdeev, Ye.V. Bibikova, T.I. Kirnozova, M.M. Futzan. Geochemistry and geochronology of Proterozoic magmatic rocks of the Ulkan trough (new evidence) 44 A.A. Sorokin, I.V. Buchko, A.B. Kotov, S.D. Velikoslavinskiy. Geochemical evidence of ophiolite nature of gabbro, gabbro-anorthosites and ultramafites of the Gerbi fragment, Baladek massif (south-eastern framing of the North Asian craton) (commented by reviewer S.V. Vysotskiy) 66 V.A. Simonov, V.S. Prihodko, S.V. Kovyazin, A.V. Tarnavsky. Petrogenesis of the Konder platinum-bearing alkali-ultrabasic massif, south-eastern part of the Aldan Shield (evidence of melt inclusions in Cr-spinels from dunites) 78 S.V. Rasskazov, V.S. Prikhodko, T.A. Yasnygina, N.N. Fefelov, Ye.V. Saranina, I.P. Voinova, S.B. Brandt. Mantle sources of Cenozoic volcanic rocks from the Kizi Lake region (East Sikhote-Alin) (commented by reviewer Yu.A. Martynov) 90 Chronicles R. Gerzonde, V.N. Karnaukh, M.S. Obrezkova. Comprehensive investigations in the northen part of the Pacific Ocean in cruise 202 of "Zonne" SRV 122 Obituary In memory of Vladimir D. Melnikov (1941–2010) 126 Konstantin F. Sergeev (1931–2010) 128 A.I. Malinovsky, M.I. Tuchkova Lithochemistry of paleoisland arc complexes as a criterion of their recognition in the paleobasins of the Russian Far East orogenic belts The lithochemical composition of terrigenous rocks from different-age and structurally contrasting paleobasins of the Russian Far East is considered. Generalization and geodynamic interpretation of the results obtained allowed us to establish the island-arc nature of these objects and to show the possibility of using lithochemistry together with other geological data for recognition of island-arc settings in the paleobasins of ancient orogenic belts. Key words: chemical composition, terrain, complex, terrigenous rocks, geodynamic settings, island arc, Far East. A.V. Maslov, A.D. Nozhkin, V.N. Podkovyrov, E.F. Letnikova, N.V. Dmitrieva, Yu.L. Ronkin Trace elements abundance ratios of Riphean fine-grained terrigenous rocks of the Uchur-Maya region and Yenisei ridge Abundance ratios (Êê) of a wide range of trace elements (Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sb, Cs, Ba, REE, Hf, Ta, Hg, Tl, Pb, Bi, Th, and U) of fine-grained terrigenous rocks (argillites, metapelites) of the Riphean reference sections of the Uchur-Maya region and Yenisei ridge are examined. It is established that clay shales and argillites of the Uchur and the Aimchan Group of the Riphean hypostratotype are moderately (2.5 < Êê < 5) and intensively (Êê > 5) Li-, B- and Zn-specialized, whereas analogous assemblages of the Lakhanda and the Ui Group display no distinct geochemical specialization, though being markedly enriched in HREE. Metapelites of basal formations of the Yenisei ridge Riphean sedimentation groups are distinctly and intensively B-specialized, and weakly Li-, Rb-, Be-, Nb-, Ta-, Th-, Ge,- and Cd-specialized. Besides, metapelites of the Lopatino and the Kordinsky Formation are moderately Cu-specialized; of Potoskui Formation, Bi-, Sb-, Hg- and V-specialized; and of Lopatino Formation, Hg- and Cs-specialized. Metapelites of the Kordinsky Formation (Lower Riphean, central zone of the Yenisei ridge) as compared with metapelites of the eastern, near-platform zone are geochemically specialized in a much greater number of elements (Li, Be, Sc, V, Cr, Co, Ni, Zn, Ga, As, Rb, Y, Zr, Nb, Sb, Ag, In, Hf, Hg, etc.), and argillites of the ore-bearing (Pb, Zn) Gorevsky Formation are distinguished by elevated concentrations of a number of ore elements (Pb, Cd, As, Sb, and Bi). Increased Êê of rare lithophyle and some ore elements in the metapelites of the Yenisei ridge is conditioned by a high sialic content – geochemical differentiation of the Early Precambrian blocks of the Siberian craton’s western margin, which were washed out in the Riphean, and riftogenic and intraplate magmatism synchronous with sedimentation. On the contrary, the fine-grained and terrigenous rocks of the Riphean lower strata of the Uchur-Maya region are compositionally close to immature substratums of the Late Archean or their Early Proterozoic analogs. Key words: abundance ratios, fine-grained terrigenous rocks, Riphean, Uchur-Maya region, Yenisei ridge. A.N. Didenko, V.A. Guryanov, A.Yu. Peskov, A.N. Perestoronin, D.V. Avdeev, Ye.V. Bibikova, T.I. Kirnozova, M.M. Fugzan Geochemistry and geochronology of Proterozoic magmatic rocks of the Ulkan trough (new evidence The paper offers new geochemical and geochronological evidence, which is suggested as the basis for the specified model of formation of the Ulkan trough. Volcanics of the Ulkan Group exhibit geochemical features proper to rocks of two recent geodynamic settings: supersubduction and within-plate. The combination of components from different-depth sources in magmatic chambers is the reason for formation of volcanics with different geochemical “indicators”. The age of granitoids of the three phases of the Ulkan massif is determined in the interval 1730–1725 Ma. The positive value åNd(T) = +3.5 and +0.7 has been established for the granites of the first and third phase. The source of melting-out of the first phase granites of the Ulkan complex were probably Paleoproterozoic rocks of juvenile crust of 1.84–1.95 Ga. The formation of effusive rocks of the Ulkan Group may be related to the geodynamic setting of the Cordilleran-type transform continental margin. The time of the action of these geodynamic conditions, judging by the model TNd(DM) age, is > 1.8 Ga. Key words: geochemistry, geochronology, paleoproterozoic, geodynamic setting, Ulkan trough, Far East. A.A. Sorokin, I.V. Buchko, A.B. Kotov, S.D. Velikoslavinskiy Geochemical evidence of ophiolite nature of gabbro, gabbro-anorthosites and ultramafites of the Gerbi fragment, Baladek massif (south-eastern framing of the North Asian craton) The Baladek massif is a tectonic block located at the boundary between the SE framing of the North Asian craton and fold structures of the Mongol-Okhotsk fold belt’s Galam terrain. According to the recent conceptions, the rocks of this massif are regarded as Precambrian assemblages of the referred craton. The paper offers investigation results of the massif fragment in the Gerbikan River basin. Geochemical data on gabbro, gabbro-anorthosites and ultramafites were obtained testifying to their similarity to rocks of typical ophiolite complexes. According to the authors, an underlying complex of metamorphic ultrabasites, a layered complex of pyroxenites and “cumulative” gabbro, gabbro-anorthosites, and a complex of “isotropic” gabbro can be distinguished. It is not impossible that also basic effusives and jaspers of the Silurian-Lower Devonian rock sequences of the Galam segment of the Mongol-Okhotsk fold belt belong to the hypothetical ophiolite complex. Key words: gabbro-anorthosites, ophiolites, south-eastern framing of the North Asian craton, Baladek massif. V.A. Simonov, V.S. Prihodko, S.V. Kovyazin, A.V. Tarnavsky Petrogenesis of the Konder platinum-bearing alkali-ultrabasic massif, south-eastern part of the Aldan Shield (evidence of melt inclusions in Cr-spinels from dunites) The investigation of melt inclusions in Cr-spinels yielded information on the physical-chemical parameters of magmatic processes responsible for the formation of the Konder platinum-bearing alkali-ultrabasic massif (south-eastern part of the Aldan Shield). A comparative analysis of compositions of chromites, containing inclusions, has shown essential differences between Konder dunite Cr-spinels and minerals of the ultrabasic complexes of ophiolites and modern oceanic crust. Compositionally and in terms of REE distribution, clinopyroxene microcrystals of the Konder massif chromites strongly differ from pyroxenes of ophiolite mafic-ultramafic complexes and are completely similar to minerals from the Kytlymsky platinum-bearing massif (the Urals). High-magnesia inclusions completely coincide by the majority of the main components with data on biotite-pyroxene alkaline picrites, which testifies to active participation of ultrabasic (picrite) alkaline magmatic systems in the process of dunite formation on the Konder massif. As a result of inclusions study by an ionic probe, direct information on the elevated contents of water (to 0.54 wt.%) in the melts was obtained. Data on distribution of rare and rare-earth elements in inclusions give evidence of the influence of the deep plume. The computed modeling on the basis of melt inclusion compositions shows that crystallization of dunites from the Konder massif was assisted by water-saturated magmas at the minimum temperatures of about 1230°Ñ. These temperatures agree with the earlier estimations of melt inclusions in olivine from the Konder massif . Key words: melt inclusions, Cr-spinels, ultramafic rocks, Konder platinum-bearing ultrabasic massif, Aldan Shield. S.V. Rasskazov, V.S. Prikhodko, T.A. Yasnygina, N.N. Fefelov, Ye.V. Saranina, I.P. Voinova, S.B. Brandt Mantle sources of Cenozoic volcanic rocks from the Kizi Lake region (East Sikhote-Alin) The Middle Cenozoic lava sequence of the Kizi Lake region has been studied. It characterizes source activity in the northern zone of the East Sikhote-Alin: a Middle Eocene impulse of over-slab magmatism and continuous Late Oligocene magma supply from under-lithosphere convective mantle. Low concentrations of highly charged microelements Nb and Ta with low Nb/Ta, Ce/Pb, Nb/La ratios and a high K/Nb ratio have been determined for the Middle Eocene dacite with an age of ~43.5 Ma, and the low ratio (87Sr/86Sr)0 0.703399 has been measured. Three phases of volcanic eruptions have been distinguished in the Late Oligocene: 1) of andesite basalts (29–27 mln years ago), 2) of trachyandesite basalts-trachyandesites (27–24 mln years ago), and 3) of andesites (~23 mln years ago). Lavas of the first and third phases showed low Ce/Pb, Nb/La, Ba/La ratios and a high K/Nb ratio, which also characterize over-slab processes. Lavas of the second phase exhibited a relative shift of these ratios toward basalt composition of ocean islands. A narrow interval of (87Sr/86Sr)0 initial strontium isotope ratios of 0.703661–0.703853 has been determined. Such ratios are proper to volcanic and subvolcanic rocks of the whole coast of Tatar Strait with an age of ~37, 31–23 and ~16 Ma. Key words: Cenozoic, basalts, microelements, K-Ar dating, Sr isotopes, Sikhote-Alin, Sakhalin. |