Early Neoproterozoic magmatism and the associated metamorphism in the Songnen Massif, NE China: Petrogenesis and tectonic implications

Abstract

Abstract Zircon U–Pb dating and geochemistry data were collected for Neoproterozoic rocks in the Songnen Massif of NE China, with the aim of understanding the extent and nature of the Precambrian basement as well as the early stages of tectonic evolution history of the massif. The newly discovered Neoproterozoic magmatism can be subdivided into three stages: (1) 929–927\u202fMa quartz-syenitic and syenogranitic gneisses, (2) ∼895\u202fMa granitic gneisses, and (3) 871\u202fMa granitic pegmatites. Associated metamorphisms can also be subdivided into two stages, i.e., the 492\u202fMa and 546–530\u202fMa, suggesting that the study area underwent two stages of metamorphism during the late Pan-African. The petrographical and geochemical data indicate that the 929–927\u202fMa syenitic rocks most likely originated from enriched mantle sources, which were metasomatized by subducted sediments and underwent fractional crystallization during ascension, whereas the ca. 895\u202fMa granitic gneisses were generated by the partial melting of ancient mafic lower crustal material. Combined with our previous study, it is suggested that the ∼929–927 and 895\u202fMa magmatism were formed in a convergent margin related to compressive orogenesis, consistent with the evolution of the Rodinia supercontinent. Similar tectono-magmatic thermal events occurred within the Songnen and Jiamusi massifs, suggesting that they could be one coherent continental unit in Precambrian.