Geochronology and geochemistry of Neoproterozoic magmatism in the Bureya Block, Russian Far East: Petrogenesis and implications for Rodinia reconstruction

摘要

The Bureya Block, located in the easternmost segment of the Central Asian Orogenic Belt (CAOB), is one of the least understood blocks in Russian Far East. Here we describe newly discovered Neoproterozoic magmatic rocks along the Bureya River in the northern Bureya Block. LA-ICP-MS zircon U-Pb dating demonstrates that these rocks were emplaced in two stages during the early Neoproterozoic: (1) 937-933 Ma, forming an intrusive rock association of gabbros, granodiorites, and monzogranites; and (2) 896-891 Ma, representing by a suite of syenogranites. The good correlation on the Neoproterozoic to Late Triassic geological events between the Jiamusi and Bureya blocks suggests the two blocks formed a contiguous crustal unit. Field observations, together with petrographic and geochemical features, and zircon Hf isotopic data, indicate a magma mixing/mingling origin for the 937-933 Ma gneissic granitoids and amphibolites, with the felsic melts generated by partial melting of a dominantly Mesoproterozoic lower crustal source with possible little addition of ancient crustal materials, whereas the mafic melts were derived from partial melting of a depleted lithospheric mantle wedge metasomatized by fluids dehydrated from the subducted oceanic slab. In addition, the 896-891 Ma syenogranites share a common crust source with the 937-933 Ma granitoids but experienced extensive assimilation and fractional crystallization during magma ascent and evolution. In the context of assembly, growth and breakup of the Rodinia supercontinent, together with the recognition of Neoproterozoic continental arc-type magmatic rocks in the Bureya-Jiamusi Block as well as the nearly coeval subduction-related magmatism recorded elsewhere on the globe, such as Seychelles, Madagascar, India, Lhasa, South China, and Australia, we conclude that the 937-891 Ma magmatism in the Bureya Block resulted from the Andean-type orogeny that formed along the northwestern margin of the Rodinia supercontinent.