Tectonic Nature of the Ul’ban Terrane (Mongol–Okhotsk Fold Belt): Results of U–Pb and Lu–Hf Isotope Studies of Detrital Zircons

The U–Pb and Lu–Hf isotope studies of detrital zircons from Mesozoic metasedimentary rocks of the Sorukan and Naldinda formations of the Ul’ban terrane are performed for the first time. It is shown that Early Precambrian zircons are almost completely absent in these rocks, while Early Mesozoic zircons with Paleozoic, Neoproterozoic, and Mesoproterozoic Hf model ages dominate. Based on the data obtained, it is assumed that the Ul’ban terrane is a part of the accretionary complex of the northern framing of the Amur superterrane and is neither a depression superimposed on the Paleozoic formations of the Mongol–Okhotsk belt nor an accretionary complex in the southern framing of the North Asian Craton, as was believed earlier.