Age and Depositional Settings of the Ordovician Chalovskaya Group in the Argun Massif, Eastern Part of the Central Asian Fold Belt

Abstract

The results of mineralogical and geochemical studies of the metaclastic rocks of the Grebnev and Magdagachi sequences of the Chalovskaya Group, one of the key lithostratigraphic units of the Argun continental massif in the eastern part of the Central Asian Fold Belt, as well as the results of the U–Pb dating of detrital zircons from these rocks by the LA-ICP-MS method, are presented. It was found that the age of the youngest zircons is ~478 Ma (Early Ordovician) in the metasandstones of the Grebnev Sequence and ~448 Ma (Late Ordovician), in the metasiltstones of the Magdagachi Sequence. Together with the previously determined age of the metadacites of the Isagachi Sequence (476 ± 8 Ma), this suggests the Ordovician age of the Chalovskaya Group, dated previously as Late Precambrian. The available data indicate that the deposits of the Chalovskaya Group accumulated in a setting of an active continental margin or an island arc against the background of intense magmatic activity. Considering that the Early Paleozoic suprasubduction magmatism is manifested in all continental massifs of the eastern part of the Central Asian Fold Belt (Argun, Mamyn, Bureya, Jiamusi, Khanka), one cannot exclude that these continental massifs have a common geodynamic history.