Periodicity of Endogenic Events of West Transbaikalia and North Mongolia (Eastern Segment of the Central Asian Foldbelt): U–Pb Age of Detrital Zircon from the Present-Day River Sediments

Five main stages of the formation and reworking of continental crust in the region are recognized on the basis of correlation between the U–Pb isotopic ages of detrital zircon grains from present-day alluvial sediments of the largest rivers of West Transbaikalia and North Mongolia and primary rocks of the Mongolian–Transbaikalian sector of the Central Asian Foldbelt: (i) Neoarchean–Paleoproterozoic (2.7–1.7 Ga), corresponding to global crust-forming processes at the basement of the Precambrian cratons; (ii) Neoproterozoic (Early and Late Baikalian) and (iii) Early Paleozoic (Caledonian), which reflect the processes of the formation of juvenile crust by means of island arc magmatism and accretion of island arcs leading to the origination of fold structures of the southern margin of the Siberian Craton; and (iv) Late Paleozoic and (v) Early to Middle Mesozoic, which reflect the processes of reworking of the Early Precambrian and Caledonian crust by intraplate magmatism and riftogenesis. It is shown that the maximum ages on the probability density curve of detrital zircon grains depend on various (often unrelated) factors, e.g., the absolute age of the rock, the area of the eroded surface, the amount of zircon in rocks of various compositions, the transportation distance, etc., and the statistics of age distribution therefore could not be used as an indicator of intensity of endogenic events. The absence of Cenozoic detrital zircon grains in alluvial sediments of the region with abundant basaltic volcanism of this period (Mongolia, Baikal region) indicates that the endogenic events, which mostly produced basalts, are omitted in the “zircon record.”