PALEOPROTEROZOIC GRANITOIDS OF THE CENTRAL PART OF THE NEPA-BOTUOBIYA ANTECLISE AS INDICATORS OF THE FORMATION OF THE TRANS-SIBERIAN OROGENIC BELT OF THE SIBERIAN CRATON
T.V. Donskaya1, D.P. Gladkochub1, M.O. Sukneva1, U.S. Efremova1, O.M. Turkina2, A.G. Vakhromeev1, E.I. Demonterova1
1Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Granitoids, U-Pb age, geochemistry, Paleoproterozoic, orogenic belt, Siberian craton
Abstract
The paper presents studies of gneisses and granitoids from three deep boreholes located in the central part of the Nepa-Botuobiya anteclise of the Siberian craton. Based on U-Pb (LA-ICP-MS) geochronological studies of zircon, the age of the granitoid protolith of amphibole-biotite gneiss from Danilovskaya BH-95 has been estimated at 2254 ± 4 Ma, the age of granitoid from Mogdinskaya BH-11, at 1972 ± 9 Ma, and the age of granitoid from Preobrazhenskaya BH-14, at 1981 ± 3 Ma. The protolith of the gneiss from Danilovskaya BH-95 corresponds in composition to granodiorite similar to I -type granite with high contents of high-field strength elements (HFSE). It is characterized by T Nd(DM) = 2.7 Ga and might have formed as a result of the melting of an Archean crustal source within a certain block. The granitoid from Mogdinskaya BH-11 has features of I -type granites with low contents of HFSE and is characterized by T Nd(DM) = 2.4 Ga. The granitoid from Preobrazhenskaya BH-14, with T Nd(DM) = 2.6 Ga, is similar to I -type granites with high contents of HFSE. All the available data and the similar ages (ca. 2.0 Ga) determined earlier for S -type gneiss-granites from one of the Danilovka group boreholes suggest the formation of granitoids with different geochemical characteristics in the central part of the Nepa-Botuobiya anteclise in the period 1.97-2.00 Ga. This was possible in the accretionary orogen including (as evidenced from the isotope characteristics) blocks with Paleoproterozoic and Archean crust. The studied area is a fragment of the Paleoproterozoic Trans-Siberian orogenic belt separating the large Archean Tunguska and Anabar superterranes. The formation of this belt marks the early stage of accretion processes and the beginning of the formation of the Siberian craton in the period 1.95-2.00 Ga.
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