Formation of the Crystalline Rock Complexes of the Tatsaingol Block of the Late Neoproterozoic Southern Khangay Metamorphic Belt, Central Asian Foldbelt

The results of geochronological studies (LA-ICP-MS) of detrital zircons of the Tatsaingol block in the southeastern part of the Neoproterozoic Southern Khangay metamorphic belt are presented. Two sequences, metaclastic rocks and hornblende schists (metavolcanics), are distinguished in the Tatsaingol complex of this block. The metaclastic rocks are found to contain manifestations of the processes of polymetamorphism. The end of the early metamorphic episode in these rocks is defined by pegmatoid granites with the ages of 561 +/- 12 and 562 +/- 2 Ma and granite dikes with the age of 571 +/- 9 Ma; the age of the late metamorphic episode is estimated in the range of 550-540 Ma. The lower age limit of metamorphism in the metavolcanics of the island arc assemblage is defined by gabbroids with the age of 603 +/- 3 Ma, but the early episode of high pressure metamorphism is not established. The late episode (550-540 Ma) is manifested in both sequences. The results of the isotopic dating of detrital zircons from biotite gneisses indicate the predominance of Paleoproterozoic and Neoarchean rocks (1.8-2.1 and 2.4-2.9 Ga, respectively) in their sources. The rocks of the island arc assemblage of the Tatsaingol complex can be viewed as a fragment of the Bayan-Khongor zone, which was accreted to the Southern Khangay metamorphic belt in the course of the accretion-collision process. The late metamorphic episode was not manifested in the central and northwestern parts of the Southern Khangay metamorphic belt, which indicates the separateness of this part of the belt from the Tatsaingol block during this period.