Neoproterozoic oblique collision along the Jiangnan Orogen, South China: Constraints from syn-orogenic crustal shearing

The precise timing and kinematics of the Neoproterozoic collisional event associated with the formation of the Jiangnan Orogen remain key unresolved issues in the tectonic evolution of the South China Block. In this study, we conducted a comprehensive investigation of structural geology for the collision-related Le’anjiang shear zone within the eastern Jiangnan Orogen, and applied apatite overgrowth rim U-Pb dating to determine the timing of shearing, providing crucial insights into these issues. Structural investigations reveal that the NE−SW-striking Le’anjiang shear zone underwent only one phase of sinistral ductile deformation, which is uniformly dominated by simple shear, comprising both narrow mylonitic belts and wide fold belts that together accommodate non-coaxial strain. Microstructural observations and electron backscatter diffraction (EBSD) fabric analyses indicate that the shear zone developed under greenschist facies conditions at temperatures of ∼300−400 °C. Laser ablation−inductively coupled plasma−mass spectrometry U-Pb dating of zircon grains and apatite cores constrains the protolith of the mylonites in the shear zone to 850−847 Ma, whereas U-Pb ages of apatite rims overgrown within mylonites constrain the timing of shear deformation to 825−820 Ma. The N−S oblique collision along the NE−SW-trending eastern Jiangnan Orogen was responsible for the sinistral motion along the Le’anjiang shear zone. The timing of the collision-induced shear zone constrains the collision to 825−820 Ma. This study emphasizes the oblique nature of the Neoproterozoic collisional event, contributing new insights into the dynamic processes involved in the formation of the Jiangnan Orogen during the Neoproterozoic.