PETROGENESIS OF COMposite DIKES IN GRANITOIDS OF WESTERN TRANSBAIKALIA
G.N. Burmakina1, A.A. Tsygankov1,2, V.B. Khubanov1,2
1Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh’yanovoi 6a, Ulan Ude, 670047, Russia
2Buryatian State University, ul. Smolina 24a, Ulan Ude, 670000, Russia
Keywords: Composite dikes, granitoids, mixing, sources of magmas, U-Pb isotopic age, formation conditions, western Transbaikalia
Abstract
The performed studies have revealed two varieties of composite dikes differing in morphology and internal structure depending on (1) the proportions of salic and basic components and (2) the rheologic state of the host environment. The latter can be both a solid substrate with open fractures and a melt at different stages of crystallization. The evaluated isotopic age of dikes in the Shaluta massif, 290.8 ± 2.7 Ma and 283.4 ± 3.4 Ma, is correlated with the time of the pluton formation. The age of the composite dike breaking through the metamorphic deposits on the eastern shore of Lake Baikal is 284.10 ± 0.96 Ma. The mass formation of composite dikes in western Transbaikalia is correlated with the Late Paleozoic magmatism, which resulted in one of the Earth’s largest granitoid provinces. The intrusion of dikes was not a single-stage event; it lasted at least 10-12 Myr and was apparently related to the repeated intrusion of large volumes of salic magmas and the formation of granitoid plutons. Early Mesozoic composite dikes associated with alkali-granitoid plutons of the Late Kunalei igneous complex (230-210 Ma) are much scarcer. Basic magmas of the composite dikes were generated at depths greater than 75 km as a result of the melting of a modified (enriched in crustal components) mantle source. Salic components of the dikes, independently of their geologic position, are generally similar in composition to the granitoids of the plutonic facies, and the differences are apparently due to hybridization proceeding at great depths.
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