COMPOSITION AND U-Pb (LA-ICP-MS) ISOTOPIC AGE OF ZIRCONS FROM COMPOSITE DIKES OF WESTERN SANGILEN (Tuva-Mongolian orogen)
A.A. Tsygankov1,2, G.N. Burmakina1, V.A. Yakovlev3,4, V.B. Khubanov1,2, V.G. Vladimirov3,4, I.V. Karmysheva3,4, M.D. Buyantuev1
1Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh’yanovoi 6a, Ulan-Ude, Russia, 670047
2Buryat State University, ul. Smolina 24а, Ulan-Ude, Russia, 670000
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Koptyuga 3, Novosibirsk, Russia, 630090
4Novosibirsk State University, ul. Pirogova 2, Novosibirsk, Russia, 630090
Keywords: Composite dikes, mingling, zircons, U-Pb isotopic age, magma sources, Western Sangilen
Abstract
Composite dikes (mingling dikes) of Western Sangilen (southeastern Tuva) are believed to indicate a shift from tectonic contraction, related to the mountain fold system formation, to postcollisional extension that ended with the disintegration of the collisional orogen. However, the position of composite dikes in the general sequence of magmatic events was based only on their geologic location and has not been confirmed by U/Pb isotope-geochronological data. The proposed study is concerned with the geologic structure, composition, and isotopic age (485-490 Ma) of West Sangilen composite dikes. The isotopic age of the host granites from the Matut pluton is 509 Ma; thermal events of Riphean (679-934 Ma) and early Paleozoic (484 Ma) ages are reflected in zircons from gneiss-granites of the Erzin metamorphic complex. The obtained data are consistent with the earlier determined sequences of West Sangilen tectonometamorphic events. Basites from the examined composite dikes are strongly different in the contents of indicator elements (Rb, Nb, Ta, Zr, and Hf) and the Nb/Y, Zr/Y, Th/Ta, Zr/Nb, and Nb/Th ratios, which is indicative of different (probably, different-depth) mantle sources. The protolith of the salic component of the combined dikes might have been rocks similar in composition to the autochthonous/parautochthonous gneiss-granites of the Erzin metamorphic complex.
DOI: 10.15372/RGG2019004
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