It still remains controversial whether the Neoproterozoic tectonic setting of the northern margin of the Yangtze Block shifted from a compressional setting to an extensional setting at 820 ~ 800 Ma, or remained a subduction setting until ~ 700 Ma. Our new identification of the Taohua bimodal volcanic rocks in the Western Dabie orogenic belt provide new constraints on the Neoproterozoic tectonic evolution and dynamic mechanism of the Yangtze Block. The SIMS and LA-ICP-MS analysis on zircons from these bimodal volcanic rocks yield consistent U-Pb ages of 750 ~ 740 Ma. The basic volcanic rocks are tholeiitic, and exhibit N-MORB-like to arc-like trace element patterns, with variable whole-rock εNd(t) values (-0.05 ~ +5.96). These basic rocks were probably generated by decompression melting of a depleted asthenospheric mantle, and magma subsequently underwent fractional crystallization and wall-rock contamination. Among the acid volcanic rocks, rocks from the Xumengzhai area are enriched in silicon (SiO2≥75%), alkalis (K2O+Na2O≥7%), REE and HFSE (i.e., Zr、Hf、Nb、Y), with high Zr+Ce+Y+Nb (≥ 600×10-6) and 10000*Ga/Al ratios (≥ 2.6), showing a close affinity to fractionated A-type granites. Their evolved zircon εHf(t) (mostly of -12.32 to -1.88) and whole-rock εNd(t) (-13.29 ~ -9.60) values indicate an evolved crustal source region, which may be generated by partial melting of Early Neoproterozoic magmatic rock rocks in the region and the magma underwent fractional crystallization. Integrating the new data with previous results for Neoproterozoic rocks from the South Qinling-Tongbai-Dabie-Sulu orogenic belt, we propose that the 780~635 Ma bimodal magmas in this belt were probably formed in a continental rift environment with episodic extension-related asthenosphere upwelling and lithosphere thinning during the middle of Neoproterozoic. Melting of asthenosphere, lithospheric mantle and crust under high-temperature and low-pressure conditions, coupled with interactions between the asthenosphere and the lithosphere, played a prominent role in the formation of the 780 ~ 635 Ma bimodal-type volcanic rocks and diverse geochemical features in the magmatic counterparts.