The Zhuangke tectonic slice crops out in the Mianlue tectonic zone at the southern margin of the South Qinling Orogen. It is widely accepted as a relict of the Mianlue ocean basin based on the tholeiitic and N- MORB (normal mid- ocean ridge basalt)- like geochemical features of its metabasalts. However, the formation age of Zhuangke metabasalts is not well understood due to the lack of high- precision geochronological constraints. Here we report, for the first time, zircon U- Pb ages of 999 ± 4 Ma and 991 ± 6 Ma for the Zhuangke metabasalts obtained by LA- ICP- MS method. Besides, our combined in- situ Lu- Hf isotopic analysis shows that these zircon separates have depleted ε Hf( t ) of +11. 00~+16.56 and single- stage Hf mode ages of 872~1108 Ma. These results clearly suggest that the metabasalts from Zhuangke tectonic slice formed in Early Neoproterozoic, and were sourced from a depleted mantle. In the framework of regional geology, we argue that the lifespan of Mianlue Ocean is Early- Middle Neoproterozoic (about 1000 to 800 Ma), rather than the long- held hypothesis of Late Paleozoic- Early Mesozoic.