Precambrian crustal evolution of the central Jiangnan Orogen (South China): Evidence from detrital zircon U-Pb ages and Hf isotopic compositions of Neoproterozoic metasedimentary rocks

The Neoproterozoic amalgamation and timing of collision between the Yangtze and Cathaysia sub-blocks along the Jiangnan Orogen in South China remain disputed. With a view to constrain the crustal evolution in this major orogen, here we present new results from petrology, geochemistry, zircon U-Pb chronology and Lu-Hf isotopes, on a suite of meta-sedimentary rocks from the Shuangqiaoshan Group and tuffaceous rock from the Liantuo Formation in the Jiuling terrane of central Jiangnan Orogen. Magmatic zircon grains in meta-sedimentary and sedimentary samples from the bottom to top part of the lower and upper Shuangqiaoshan groups constraints the deposition during 863-820 Ma and 797-780 Ma, respectively. The unconformities were formed during 820-797 Ma, reflecting the final amalgamation of Yangtze with Cathaysia sub-blocks along the central Jiangnan Orogen. Our data also identify four major events at 1000-800, 1500-1900, 1900-2200, 2300-2600 Ma. The Neoproterozoic detrital zircons in the lower Shuangqiaoshan Group possess variable εHf(t) values of −44.0 to +13.4. Combined with the geochemical features, these data suggest that the lower Shuangqiaoshan Group was deposited in a back-arc basin with a mixed provenance of granitic and felsic volcanic components, whereas the upper Shuangqiaoshan Group was formed in a rift basin with more granitic or felsic components in the source region. Integrating the results presented in this study with those from previous works, a five-stage crustal evolution model is proposed for the Neoproterozoic Jiangnan Orogen involving (1) intra-oceanic subduction beneath the Huaiyu oceanic island arc (1000-880 Ma), (2) collision between Huaiyu arc and Yangtze Sub-block (880-860 Ma), (3) back-arc extension beneath the Yangtze Sub-block (860-830 Ma), (4) collision between Cathaysia and Yangtze sub-blocks (830-800) and (5) intracontinental rifting throughout South China Block (800-750 Ma).