Abstract:Objectives:The fragmentary ophiolite fragments distributed in the Jiangnan orogenic belt have important geological significance for constraining the tectonic evolution of the Jiangnan orogen. Combined with petrological study and SHRIMP UPb zircon ages of the northeastern Jiangxi ophiolites and the Zhangcun Group, we briefly discuss the tectonic evolution of the Jiangnan orogen. Methods: Based on the field work, through the microscope observation, the whole rock chemical analysis, the the O isotopic analysis and SHRIMP UPb zircon dating of the Zhangshudun ophiolite and tuffaceous phyllite of of the Zhangcun Group. Results: The geochemical analyses of mafic—ultramafic rocks in the Zhangshudun ophiolite show that the gabbro yields the MORBlike geochemical composition and the serpentinite is strongly depleted in the trace elements. The SHRIMP O isotope analyses of zircons in gabbro yield homogeneous O isotope (5.12‰ ± 0.62‰,2 ), similar to the O isotope of zircons in mantle (5.3‰ ± 0.3‰). These geochemical characters support that these rocks represent remnants of ancient oceanic crust and upper mantle. SHRIMP U-Pb zircon analyses yields the formation age of 1009 ± 5 Ma (MSWD = 1.15) for the gabbro in the Zhangshudun ophiolite. As the surrounding rocks of the Northeastern Jiangxi ophiolite, the formation age of the Zhangcun Group is constrained by the SHRIMP UPb zircon dating of a tuffaceous phyllite which yields the formation age of 833 ± 10 Ma (MSWD = 1.5). This age suggests the emplacement of Northeastern Jiangxi ophiolite is later than 833 Ma. Conclusions: Combined with the early research, we suggest that the Northeastern Jiangxi ophiolite formed at the midocean ridge environment in lateMesoproterozoic to earlyNeoproterozoic, different from the midNeoproterozoic backarc basin represented by the Fuchuan ophiolite in the south Anhui province. These new data provide new constrains for tectonic evolution of South China.