Age and Sources of Terrigenous Rocks of Basal Formation of the Tsagaan-Olom Group of the Dzabkhan Terrane: Results of U–Th–Pb Geochronological, Lu–Hf and Sm–Nd Isotopic Studies

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The results of U–Th–Pb geochronological (LA-ICP-MS) and Hf isotope (LA-MC-ICP-MS) studies of detrital zircons from sandstones and also the results of Nd isotope studies of whole rocks from the tillite-bearing Maikhan-Uul Formation of the Tsagaan-Olom Group of the shelf cover of the southeastern part of the Dzabkhan terrane of the Central Asian Orogenic Belt are considered. The obtained data made it possible to establish that the sources of sandstones of the Maikhan-Uul Formation of the Tsagaan-Olom Group were rocks of the Neoproterozoic and the Early Precambrian complexes with Archean and Paleoproterozoic Hf and Nd model ages, as well as Neoproterozoic igneous rocks formed from both juvenile and crustal sources. The age of the sandstones of the Maikhan-Uul Formation is in the range of ca. 720–660 Ma. It is shown that a large-scale manifestation of convergence processes with the formation of the juvenile crust and the reworking of the ancient continental crust is established in the structures of the central segment of the Central Asian Orogenic Belt in the Early Neoproterozoic (ca. 960–780 Ma). Most likely, these processes reflect the development of the global subduction system in the paleooceanic region of the Rodinia supercontinent margins.