Formation of the Neoproterozoic Continental Crust in the Structures of the Central Segment of the Central Asian Fold Belt

Abstract

The paper considers the results of geochronological (U-Pb method, ID-TIMS), geochemical, and Sm-Nd isotopic studies of granitoids, volcanics, and terrigenous rocks of the eastern Dzabkhan terrane, as well as felsic volcanics of the Dzabkhan Formation in its southern part. It is established that the post-kinematic granitoids of the Dzabhan–Mandal Zone, Erdenekhairkhan, and Bogdoingol blocks were formed in the range of 813 ± 9–772 ± 3 and ca. 720 Ma, and the rhyolites of the Dzabkhan Formation were formed at 790 ± 3 Ma. The rock sources in the southern part of the terrane and in the Bogdoingol Block were mainly ancient crustal complexes. Nd isotopic data on the rocks of the Dzabkhan–Mandal Zone and the Erdenekhairkhan Block demonstrate the mixed nature of their sources and suggest a significant contribution of Early Neoproterozoic juvenile material. Based on obtained and previous data, it is shown that the Dzabkhan terrane is not a homogeneous block of the Early Precambrian continental crust, but represents a Neoproterozoic composite terrane consisting of rocks of island arc and continental margin complexes, and reworked Early Precambrian continental crust. The correlation of the Precambrian complexes of the Dzabkhan terrane with those of the Songino, Baidarik, and Tarbagatai terranes is discussed, and features of the formation of the Neoproterozoic continental crust in the central segment of the Central Asian fold belt are considered. It is established that the Khangay group terranes comprise widespread oceanic, island arc, continental margin, and riftogenic complexes formed at ca. 960–930, 880–850, and 810–790 Ma. Based on the data obtained, a model of the formation and evolution of the Neoproterozoic crust of the Central Asian fold belt is proposed by the example of paleoreconstructions for 925 and 825 Ma. It is assumed that the extensive growth of the Neoproterozoic continental crust of the region was related to the subduction processes in the framing of the Rodinia supercontinent at about 960–860 Ma ago and continental rifting that initiated the breakup of the supercontinent in the middle Tonian at about 860 and 800 Ma ago.