Abstract
Results of U-Pb and Lu-Hf isotopic studies on detrital zircons from metasedimentary rocks in the eastern part of the Selemdzha and Tokur terranes of the Mongol-Okhotsk belt and Sm-Nd isotopic data for whole-rocks are in complete contradiction with existing ideas about the stratigraphy of the region under consideration and indicate the need to revise the traditional principles of mapping within the belt. Two types of deposits have been established, differing in Sm-Nd isotopic characteristics of whole-rocks and Lu-Hf isotopic composition of detrital zircons. Deposits of different types are involved in the formation of the two opposing accretion systems: in front of the Siberian Craton margin (type I) and the Amur superterrane (type II). Among type I deposits, discrete groups are distinguished that differ in the lower age limit: 553–498 Ma, Late Ediacaran-Cambrian; ~373 Ma, Upper Devonian; 333–327 Ma, Upper Mississippian; ~304 Ma, Pennsylvanian. The deposits of tectonic-stratigraphic units show a general pattern of younging from north to south. Thus, we observe a structure typical of accretionary wedge-shaped terranes with a rear part in the north and a frontal part in the south. Tectonic-stratigraphic units formed by type I deposits and previously considered part of the Selemdzha and Tokur terranes, apparently, are components of the Galam terrane of the accretionary wedge.
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