Frequency of Endogenous Events in Western Transbaikalia and Northern Mongolia (Eastern Segment of the Central Asian Orogenic Belt) According to U–Pb Dating of Detrital Zircon Grains from Modern Fluvial Deposits

Abstract

Based on the correlation of U–Pb isotopic age of detrital zircon grains from modern fluvial deposits of the largest rivers of Western Transbaikalia and Northern Mongolia and U–Pb isotopic ages of bedrock of the Mongol-Transbaikal sector of the Central Asian Orogenic Belt, five main stages of formation and processing of the continental crust are identified in the region: (1) the Neoarchean-Paleoproterozoic stage (2.7–1.7 Ga), corresponding to the global crust-forming processes of the Precambrian cratons’ basement formation; (2) the Neoproterozoic (early and late Baikal) and (3) the Early Paleozoic (Caledonian) stages reflecting the processes of formation of juvenile crust through island-arc magmatism and accretion of island arcs, which led to the formation of folded structures of the southern margin of the Siberian craton; (4) the Late Paleozoic and (5) Early-Middle Mesozoic stages reflecting the processing of the Early Precambrian and Caledonian crust through intraplate magmatism and riftogenesis. It is shown that the peak values of the probability density distribution curve of the detrital zircon grains’ age depend on various, often unrelated factors, such as the absolute age of the rock, the area of the eroded surface, the amount of zircon in rocks of different composition, the distance of transport, etc., therefore, the statistics of age distribution cannot be considered as an indicator of the intensity of endogenous events. The absence of Cenozoic grains of detrital zircon in the fluvial deposits of the region where basalt volcanism of this time is widely manifested (Mongolia, Baikal region) indicates that endogenous events, which are mainly expressed in basalts, are not manifested in the “zircon chronicle”.