Petrogenesis of ca. 830 Ma Lushan bimodal volcanic rocks at the southeastern margin of the Yangtze Block, South China: Implications for asthenospheric upwelling and reworking of juvenile crust

•Lushan mafic rocks are derived from a fluid-modified depleted mantle.•Lushan felsic rocks created by partial melting of juvenile meta-igneous rocks at shallow crust.•Both depleted and enriched mantle source can be discriminated in the southeastern margin of the Yangtze Block at ca. 830 Ma.•Ca. 850 Ma magmatic rocks may be more extensive than previous thought. Neoproterozoic bimodal volcanic rocks are widespread in the South China Block and provide information on crust–mantle interaction, the thermal and chemical status of the deep mantle, and the growth and reworking of continental crust. In this paper, we present sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb ages and whole-rock geochemistry for the Lushan bimodal volcanic rocks in northern Jiangxi Province, South China Block. Our SHRIMP dating indicates that the Lushan bimodal volcanic rocks were erupted at 835–820 Ma. The least-evolved mafic rocks have high εNd(t) (+8.3) and “arc-like” Nb/La and Nb/Th ratios, thier derivation from fluid-modified depleted mantle. The melts that formed these mafic rocks underwent fractional crystallization involving mineral assemblages of olivine + plagioclase → clinopyroxene + plagioclase at MgO