Age and sources of melts of metavolcanic rocks of the Djagdagle formation of the northwestern part of the Bureya continental massif, Central Asian Orogenic Belt

The paper presents the results of U–Pb (ID-TIMS) geochronologic, geochemical, Sm–Nd isotopic-geochemical studies of metavolcanic rocks of the Djagdagle formation, which are among the key elements in the structure of the Bureya continental massif. It was established that the age of metavolcanic rocks of the Djagdagle formation is 217 ± 7 Ma and corresponds to the Late Triassic. This fact contradicts the traditional ideas, according to which the Early Precambrian age is attributed to the Djagdagle formation. The results of Sm–Nd isotope studies of the considered metavolcanic rocks indicate the melting of rocks of continental crust with Paleoproterozoic model ages during the formation of their initial melts. The new geochronologic data and previously published data allow us to distinguish at least two stages of magmatic activity in the Triassic within the northwestern part of the Bureya massif ~243 and 219–201 Ma. On the basis of synchronous manifestation of Neoproterozoic, Early Paleozoic, Late Paleozoic and Early Mesozoic magmatic events in the history of geologic development of the Bureya and Songnen– Zhangguangcai Range massifs, an assumption about their common geological history at least since the Late Neoproterozoic has been put forward. The close spatial position of metavolcanic rocks of the Djagdagle formation with Mongol–Okhotsk orogenic belt, their Late Triassic age (217 ± 7 Ma) and geochemical features allow us to link the formation of initial melts of metavolcanic rocks of the Djagdagle formation with within-plate magmatism in the rear zone of subduction of the Mongol–Okhotsk Ocean beneath the northern (in modern coordinates) margin of the Bureya continental massif.