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Shemin G.G.,Russian Academy of Sciences | Chernova L.S.,Siberian Research Institute of Geology | Potlova M.M.,Siberian Research Institute of Geology | Vashchenko V.A.,Irkutskgeofizika Federal State Geological Enterprise | And 2 more authors.
Russian Geology and Geophysics | Year: 2012

We present results of lithofacies, reservoir, geochemical, well logging, and petrophysical studies of the key section of the Vendian-Lower Cambrian Preobrazhenka productive horizon in the Lena-Tunguska province. We have considered the composition, structure, and formation conditions of the deposits as well as the intensity of postsedimentation processes and the rock geochemistry, petrophysics, and reservoir properties. © 2011. Source

Donskaya T.V.,Russian Academy of Sciences | Gladkochub D.P.,Russian Academy of Sciences | Mazukabzov A.M.,Russian Academy of Sciences | De Waele B.,SPK Consulting | Presnyakov S.L.,Ap Karpinsky All Russian Research Geological Institute
Russian Geology and Geophysics | Year: 2012

The Kataev volcanoplutonic association has been recognized in western Transbaikalia. It unites the volcanosedimentary rocks of the Kataev Formation and associated granites localized within the lower plates of the Buteel-Nuur and Zagan metamorphic-core complexes. The rocks of the Kataev association are dynamometamorphosed to different degrees, which is due to the tectonic exposure of metamorphic-core complexes in the Early Cretaceous. The U-Pb zircon dating of the Kataev Formation rhyolites yielded an age of 226 ± 3 Ma. The U-Pb zircon age of the granites intruding the Kataev Formation rocks is 223.4 ± 5.0 Ma. The volcanics of the Kataev Formation belong to the subalkalic basalt-andesite-dacite-rhyolite series. The trachybasalts and trachyandesite-basalts of the Kataev Formation have geochemical characteristics of igneous rocks formed as a result of subduction, e.g., they show distinct negative Nb and Ti and positive Ba and Sr anomalies on multielemental patterns. The specific composition of mafic volcanics points to their formation through the melting of a mantle source resulted from the mixing of depleted mantle and subduction components. Trachyandesites have higher Th and U contents than basaltoids. They can result from the contamination of a mantle source, similar in composition to the Kataev Formation basaltoids, with crustal material. The felsic volcanics of the Kataev Formation and granites intruding them show nearly identical geochemical characteristics corresponding to both A-and I-type granites. These rocks might have formed through the melting of a moderately water-saturated magmatic source of diorite-tonalite composition at 742-833°C. We have established that the rocks of the Kataev volcanoplutonic association in western Transbaikalia and Northern Mongolia formed in the Late Triassic synchronously with the calc-alkaline granitoids of the Henteyn-Daurian batholith and the alkali granites and bimodal volcanic associations of the Kharitonovo and Tsagaan-Hurtey volcanoplutonic associations. The synchronous formation of volcanoplutonic associations of normal and high alkalinity agrees with the geodynamic setting of the Andean-type active continental margin existing in the area of present-day western Transbaikalia and Northern Mongolia in the Early Mesozoic. This setting was the result of the subduction of the Mongol-Okhotsk oceanic plate beneath the Siberian continent. © 2011. Source

Doroshkevich A.G.,Russian Academy of Sciences | Ripp G.S.,Russian Academy of Sciences | Sergeev S.A.,Ap Karpinsky All Russian Research Geological Institute | Konopel'ko D.L.,Saint Petersburg State University
Russian Geology and Geophysics | Year: 2012

We present results of U-Pb (SHRIMP II) geochronological study of the rocks of the Mukhal alkaline massif in the Vitim alkaline province, western Transbaikalia. The available K-Ar and Rb-Sr dates for the alkaline rocks (Saizhen complex) of the Vitim province, including the Mukhal massif, vary over a broad range of values. The obtained age of crystallization of the Mukhal urtites refines the time when the regional alkaline magmatism began. The age of zircons and magmatic processes within the Barguzin area (315-275 Ma) is close to the peak of main events, which occurred between 295 and 275 Ma. These processes took place at the early stage of evolution of the Late Paleozoic rift system in Central Asia, whose activity was associated with the activity of mantle superplume. © 2011. Source

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