Abstract:The Neoproterozoic tectonic evolution of the northern Yangtze Block remains controversial, with ongoing debate whether it transitioned from compressional to extensional at 820~800 Ma or persisted as a subduction setting until around 700 Ma. This study presents new data on the Taohua bimodal volcanic rocks in the West Dabie orogenic belt, providing novel constraints on the Neoproterozoic tectonic evolution and dynamic mechanisms of the Yangtze Block. SIMS and LA- ICP- MS zircon U- Pb dating of these bimodal volcanic rocks yields consistent ages of 750~740 Ma. The basic volcanic rocks display tholeiitic characteristics and exhibit N- MORB- like to arc- like trace element patterns, with variable whole- rock εNd(t) values ranging from 0. 05 to +5. 96. These observations suggest that these basic rocks were probably generated by decompression melting of a depleted asthenospheric mantle, followed by fractional crystallization and wall- rock contamination. The acid volcanic rocks from the Xumengzhai area are enriched in silicon (SiO2≥75%), alkalis (K2O+Na2O≥7%), REE and HFSE (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 12. 32 to 1. 88) and whole- rock εNd(t) (13. 29 to 9. 60) values indicate an evolved crustal source, potentially generated by partial melting of Early Neoproterozoic magmatic rocks in the region, followed by fractional crystallization. The integration of these new findings with previous studies of Neoproterozoic rocks in the South Qinling- Tongbai- Dabie- Sulu orogenic belt leads to the proposition that the 780~635 Ma bimodal magmas in this belt were probably formed in a continental rift environment characterized by episodic extension- related asthenosphere upwelling and lithosphere thinning during the middle Neoproterozoic. This scenario implies that melting of the 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 their diverse magmatic geochemical features.