Zircon SHRIMP U-Pb dating of the igneous rocks from Chengbu, Hunan, and their constraints on the Neoproterozoic tectonic evolution of Jiangnan orogenic belt Bai Daoyuan1 Jia Baohua2 Liu Wei1 Chen Bihe1 Liu Yaorong1 Zhangxiang1 1. Hunan Institute of Geology Survey, Changsha, Hunan 410011, China; 2. Hunan Bureau of Geology and Mineral Resources Exploration and development, Changsha, Hunan 410011 Abstract: There exist different recognitions about the middle Neoproterozoic tectonic evolution of the Jiangnan orogenic belt (JOB) and the tectonic affinity of the southwestern section of Qinzhou-Hangzhou juncture. Zircon SHRIMP U-Pb dating was performed for the Neoproterozoic volcanic rocks and granites in the Chengbu area, Hunan, and their tectonic settings were confirmed, which gives some constraints on regional tectonic evolution. The Chengbu Neoproterozoic granites intruded the metamorphic volcanic-sedimentary sequences of the Yunchangli Formation, and the zircon SHRIMP U-Pb dating work yield (828±10)Ma and (805.7±9.2)Ma for the volcanic rock and granites, respectively. Combined studies on the major and trace elements suggest an island arc setting for the granites and a fore-arc basin of active continental margin for the Yunchangli Formation. Based on the study of the Chengbu volcanic rocks and granites as well as the regional geologic analysis, the authors put forward a new model for the Neoproterozoic tectonic evolution of the western section of JOB. During 872~835 Ma a continental margin basin developed in the area; during 835~820 Ma subduction-related orogenesis took place in JOB which resulted in the formations of mafic-ultramafic rocks and the early phasic island arc granodiorites, while Chengbu area to the east of JOB was forearc basin; during 820~810 Ma there arc-continental collision happened; during 810~800 Ma JOB turned to be in a post-collisional setting and the strong peraluminous granites were formed, while a new island arc was formed in Chengbu area for the ocean crust subduction of Huanan ocean; South China got into rifting basin stage since 800Ma. Above achievement revealed a series of island arc accretion processes in the southeastern margin of Yangtze block, and provided important evidence for the Xuefeng Period “remnant ocean basin” attribute of the southwestern section of Qinzhou-Hangzhou juncture. Key words: zircon SHRIMP U-Pb dating; granites and volcanic rocks; tectonic evolution; Neoproterozoic; Chengbu; Jiangnan orogenic belt