Petrogenetic and tectonic implications of mid–Neoproterozoic I–type granites in the Feidong Complex on the northeastern margin of the Yangtze Block, South China

Abstract

Neoproterozoic magmatic rocks are widely distributed along the periphery of the Yangtze Block, but their petrogenesis and tectonic setting remain controversial. This study involved an integrated geochemical and geochronological analysis of mid–Neoproterozoic granitic rocks from the Feidong Complex on the northeastern margin of the Yangtze Block. LA–ICP–MS zircon U–Pb dating of two granitic gneiss samples yielded weighted mean ages of 803 ± 7 Ma and 792 ± 11 Ma. Combined with published age data from other Neoproterozoic magmatic rocks, these new dates suggest that the Feidong Complex experienced a magmatic flare–up at ca. 800 Ma. Geochemically, the granitic gneisses exhibit the characteristics of highly fractionated I–type granites. All of the studied samples have negative εHf(t) values of –18.20 to –8.51 and corresponding two–stage Hf model ages (TDM2) of 2.82–2.23 Ga, indicating their derivation from remelting of ancient crust. Geochemical characteristics suggest that the granitic rocks formed in a syn–collisional or post–orogenic environment. Integrating published geochemical data from other magmatic rocks along the northern margin of the Yangtze Block, we suggest that a plausible petrogenetic model for mid–Neoproterozoic magmatic rocks within the Feidong Complex may be tectonic collapse and remelting of the early to mid–Neoproterozoic collisional orogenic belt. In this model, melting represents a tectonothermal response to lithospheric extension before the breakup of the Rodinia supercontinent.