Precambrian Evolution Of The Jiangnan Orogenic Belt

The Jiangnan orogenic belt is a Neoproterozoic collision zone between the Yangtze and Cathaysia Blocks, its collision timing and history of evolution were long-time debated. This paper presents results from zircon U-Pb geochronology and Lu-Hf isotopes from detrital zircons of sedimentary and meta-sedimentary rocks of the Jiangnan orogenic belt. In the eastern Jiangnan orogenic belt, the sedimentary sequences in southwestern Huaiyu terrane have characteristic of fore-arc basin; U-Pb dating data from detrital zircons yield a single age population of 800-900 Ma. Whereas the sedimentary sequences in the northeastern Huaiyu terrane have an arc affinity; the dating data concentrate in the range 800-950 Ma. And in the western Jiangnan orogenic belt, U-Pb dating data from detrital zircons of meta-sedimentary rocks of basement Lengjiaxi Group concentrate in the range 780-930 Ma, sedimentary sequences also have an arc affinity. However, detrital zircons from the Jiangnan orogenic belt cover sequence preserves multiple sources with age populations of 730-950 Ma,1625-2120 Ma and 2305-2680 Ma. Moreover, Hf isotopic compositions reveal that most detrital zircons from the Jiangnan orogenic belt basement yielded positive ?Hf(t) values and late Mesoproterozoic model ages, suggesting that they soured from a Neoproterozoic arc; while those of cover sequence show negative ?Hf(t) values, indicating multiple sources. the geochronological and Hf isotopic data witness that an assembly of the Yangtze and Cathaysia Blocks, being finished at ca.800 Ma. Therefore, there is an insight for evolution of the Jiangnan orogenic belt:(1)plate subduction at ca.1.0-0.86 Ga with sedimentation at fore-arc and back-arc; (2) collision and assembly at ca.860-800 Ma; (3)breakup at ca.800-750Ma. Moreover, for location of Huanan block in Rodinia, we suggest a marginal position of the supercontinent.