EARLY PRECAMBRIAN GRANITOID MAGMATISM OF THE KITOI BLOCK AND STAGES OF COLLISION EVENTS IN THE SOUTHWESTERN SIBERIAN CRATON
O.M. Turkina, V.P. Sukhorukov
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Granitoids, early Precambrian, Neoarchean collision, crustal recycling
Abstract
The paper presents the U-Pb age of zircons and the geochemical and isotope characteristics of granitoids from the Kitoi block (Sharyzhalgai uplift, southwestern Siberian craton). The studied granitoids compose different-scale vein bodies. According to the structural relations among the rocks and their U-Pb zircon ages, there were three stages of early Precambrian granite formation: ~2.99, 2.54, and 1.88 Ga. The Neoarchean and Paleoproterozoic granites contain inherited zircons dated at ~2.97-3.00 Ga, which are close in age to magmatic zircons from the Mezoarchean granite-gneiss. The Kitoi granitoids of different ages show similar enrichment in SiO2, K2O, and incompatible trace elements. In trace element composition and crystallization temperatures the Mesoarchean granite-gneisses are similar to A-type granites, while the Neoarchean and Paleoproterozoic granitoids, to I-type ones. The inherited ~2.97-3.00 Ga zircons and narrow range of model Nd ages ( T Nd(DM) = 3.0-3.3 Ga) indicate that the Neoarchean and Paleoproterozoic granitoids formed through the recycling of the Mesoarchean crust. The Neoarchean (~2.54 Ga) and Paleoproterozoic (~1.88 Ga) stages of granite emplacement in the northwest of the Kitoi block correlate with the formation of granitoids and high-temperature metamorphism in the Irkut block and the border zone between the two blocks. The subsynchronous granite formation and metamorphism (~2.54 Ga) give strong evidence that the amalgamation of the Kitoi and Irkut blocks resulted from collisional orogeny in the terminal Neoarchean.
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