COLLISIONAL MAFIC MAGMATISM OF THE FOLD-THRUST BELTS FRAMING SOUTHERN SIBERIA (Western Sangilen, southeastern Tuva)
R.A. Shelepaev1,2, V.V. Egorova1,2, A.E. Izokh1,2, R. Zeltmann3
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3Natural History Museum, CERCAMS, London, Cromwell Road, SW7 5BD, UK
Keywords: Коллизионный ороген, базитовый магматизм, кембро-ордовикская коллизия, перидотит-габбровые, габбро-монцодиоритовые, дунит-верлит-клинопироксенит-габбровые, щелочно-базальтовые ассоциации, юг Сибири, Collisional orogen, mafic magmatism, Cambrian-Ordovician collision, peridotite-gabbro, gabbro-monzodiorite, dunite-wehrlite-clinopyroxenite-gabbro, and alkali basalts, southern Siberia
Abstract
We consider geochemical features of mafic magmatism manifested during the evolution of a complex nappe-folded structure in Western Sangilen, resulted from the Cambrian-Ordovician collisional tectogenesis. There are abundant ultramafic-mafic and mafic associations of different types in this region: layered low-Ti low-alkali ultramafic-mafic intrusions, high-Ti medium-alkali gabbroids, gabbro-monzodiorite intrusions, and alkali basalts. Isotope-geochronological data showed that these complexes formed over a wide time interval, from 570 to 440 Ma. At this time, the geodynamic setting in Western Sangilen changed from an island-arc one via a collision one to an intercontinental rift setting. At the early and late stages of the evolution of Western Sangilen, the geochemical features of mafites were typical of their geodynamic settings. The properties of mafites that formed synchronously with the collision are of particular interest. The studies have shown that the chemical composition of collisional mafites of Western Sangilen changed with time. They became richer in alkalies, titanium, and incompatible elements. This fact indicates a change in the type of mantle source from suprasubductional in the Cambrian to enriched deeper-level one in the Ordovician.
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