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T. A. Myskova N. M. Ivanov M. A. Korsakova R. I. Milkevich S. L. Presnyakov N. G. Berezhnaya 《Stratigraphy and Geological Correlation》2012,20(1):1-14
During this work, the composition of Sariolian volcanites of the Vermas formationin the Karelian region was studied and the
U-Pb age of these rocks was first obtained (SHRIMP-II). In composition these volcanites are andesites and andesite-basalts,
as well as, to a lesser extent, trachyandesites and trachyandesitobasalts of the calc-alkaline series. Due to porphyroblast
crystallization, widely manifested in this region volcanites are enriched in TiO2, Al2O3, Fe2O3total, K2O, Rb, Cs, Zr, Hf, Y, Nb, Cr, V, Th and REE (primarily La and Ce). Rocks of the Vermas formation formed in the Paleoproterozoic
(2412 ± 17 Ma) and were transformed as a result of the Svecofennian metamorphism in the interval of 1970 ± 15 Ma. The source
of the melt and inherited zircons with the age of 2630–2760 Ma can be crustal material with the ancient Sm-Nd model age (3–3.1
Ga). 相似文献
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An analytical technique is proposed to determine ultratrace concentrations of Mo, V, and W found in seawater using mass spectrometry with inductively coupled plasma (ICP MS) after preliminary concentration by solid-phase extraction of metal complexes with 8-hydroxyquinoline (8-HQ) on C18 octadecyl silica. The technique utilizes 150 mL of a water sample. A preconcentration factor 50 is obtained. The detection limits are 0.25 nmol/kg, 0.041 nmol/kg, and 5 pmol/kg for Mo, V, and W, respectively. Dissolved Mo, V, and Wconcentrations in surface seawater from Atlantic Ocean transect were determined. The concentrations ranges along the transect were: 91–108 nmol/kg for Mo, 28–35 nmol/kg for V, and 55–75 pmol/kg for W. The Mo/W ratio varied from 1300 to 1800. 相似文献
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O. M. Turkina N. G. Berezhnaya L. N. Urmantseva I. P. Paderin S. G. Skublov 《Doklady Earth Sciences》2009,429(2):1505-1510
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O.M. Turkina N.G. Berezhnaya A.N. Larionov E.N. Lepekhina S.L. Presnyakov T.E. Saltykova 《Russian Geology and Geophysics》2009,50(1):15-28
In the northwestern part of the Sharyzhalgai uplift of the Siberian craton (Bulun block), the earliest sialic crust (grey-gneiss complex) is composed of plagiogneisses, their migmatized varieties, and subordinate plagiogranitoids. The petrochemical, trace-element, and Sm-Nd isotope compositions of rocks were studied, and U-Pb dating of zircons (SHRIMP II) was performed. Plagiogneisses and plagiogranitoids of trondhjemite and, more seldom, tonalite compositions are predominant; their compositions are typical of rocks of Archean tonalite-trondhjemitegranodiorite (TTG) complexes (Al2O3 ≥ 15%, Mg# = 28–38, (La/Yb)n = 23–66, Sr/Y = 27–135, Eu/Eu? = 0.7–1.1). Plagiogneisses of meta-andesite-rhyodacite association are subordinate (SiO2 = 59–69%, (La/Yb)n = 7–32, Sr/Y = 11–24, Eu/Eu? = 0.5–0.7). Cathodoluminescent study of zircons revealed “magmatic cores” and metamorphic rims; most of the rims differ from the cores in U and Th contents and low or greatly varying Th/U ratios. In migmatized plagiogneisses of trondhjemite composition, two zircon generations of different morphologies have been recognized. The protoliths of the grey-gneiss complex rocks formed in the Paleoarchean as a result of two discrete magmatic events, at ～3.3 and 3.25 Ga, and their metamorphism and migmatization took place at ～3.2 Ga. The isotopic and geochemical features of rocks evidence that the primary melts were produced mainly through the melting of metabasic sources at different depths of the thickened crust. Plagiogneisses of trondhjemite composition apparently resulted from magma generation involving ancient sialic material. 相似文献
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S. A. Sergeev S. B. Lobach-Zhuchenko N. A. Arestova E. V. Tolmacheva N. G. Berezhnaya D. I. Matukov K. I. Lokhov A. V. Antonov 《Geochemistry International》2008,46(6):595-607
The structure and composition of accessory zircons from the tonalites of the Vyg River, southeastern Karelia, were investigated. Their local U-Pb SHRIMP dating yielded ages between 3127±15 and 3146±25 Ma. It was shown that the zircons consist of three zones, a central part containing solid and melt inclusions and zoned magmatic and metasomatic shells. The obtained ages correspond to the magmatic and metasomatic stages of zircon crystallization. In general, the zircons have elevated contents of LREE (up to 867 ppm La), which were mainly accumulated in the outer metasomatic shell. Apatite and CO2 inclusions are widespread. Orthoclase, orthopyroxene, ilmenite, galena, quartz, and bastnaesite were identified in a solid inclusion in one zircon core using a CAMSCAN MX 2500 electron microscope. The presence of bastnaesite accentuates the relation of LREE with a CO2-rich fluid. It was shown that REE content is not correlated with U, Th, and U/Th ratio. 相似文献