EARLY CRETACEOUS GRANITOIDS OF THE SOKTUY MASSIF (EASTERN TRANSBAIKALIA): FEATURES OF COMPOSITION AND PETROGENESIS
A.V. Naryzhnova1,2, N.N. Kruk1,2, S.Z. Smirnov1,2,3, Kotler P.D.1,4, A.V. Kulikova4, N.S. Bortnikov5, V.S. Antipin6, E.N. Moroz1, A.S. Volosov1, A.S. Borisenko1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Tomsk State University, Tomsk, Russia
4Kazan Federal University, Kazan
5 Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences, Moscow
6Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: rare metal granites, geochemistry, mineralogy, fluid regime, petrogenesis, Transbaikalia
Abstract
The paper deals with the age, composition and features of the genesis of granitoids of the Soktuy massif – the petrotype of the Kukulbey complex of Mesozoic rare-metal granites of Transbaikalia. The Soktuy massif is heterogeneous. Several petrographic varieties are distinguished: monzo- granite-leucogranites and microleucogranites of the main intrusive phase, alaskites, alkali-feldspar granite porphyries, granodiorites and quartz syenites of the additional intrusion phase According to the obtained U-Pb-geochronological data, the age of all varieties is indistinguishable taking into account the analytical error and corresponds to the Early Cretaceous. Granitoids differ in a variety of geochemical characteristics: monzo- granite-leucogranites of the main intrusive phase belong to the rare-metal-plumasite type, rocks of the phase of additional intrusions show signs of A-type granitoids. The geochemical and isotopic characteristics of the rocks indicate the participation in their formation of both substrates of the continental crust and deep magmas of mantle genesis. The volatile content in micas and the peculiarities of the composition of inclusions indicate that the formation of magmas occurred with the participation of two types of fluids: chloride and reduced (probably mantle) and more oxidized fluoride (presumably having a lower-crust nature). All melts were generated at depths of no more than 30 km, and the depth of formation of the massif did not exceed 8 km. Based on the obtained data set, a model for the formation of rocks of the massif is proposed.
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