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.

This article presents the results of U–Pb (ID-TIMS) geochronological, geochemical, and Sm–Nd isotopic-geochemical studies of metavolcanic rocks of the Djagdagle Formation, which belong to the key elements 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 Djagdagle formation is the Early Precambrian in age. The results of Sm–Nd isotope studies of the metavolcanic rocks indicate the melting of rocks of continental crust with Paleoproterozoic model ages during the formation of initial melts. The new geochronological 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 of Neoproterozoic, Early Paleozoic, Late Paleozoic, and Early Mesozoic magmatic events in the geologic history of the Bureya and Songnen–Zhangguangcai Range massifs, an assumption about their common geological history at least since the Late Neoproterozoic has been proposed. The close spatial position of metavolcanic rocks of the Djagdagle Formation and the 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 this formation with within-plate magmatism in the rear part of subduction zone of the Mongol–Okhotsk Ocean beneath the northern (in modern coordinates) margin of the Bureya continental massif. [ABSTRACT FROM AUTHOR]