Sedimentological Features of the Xiajiang Group and Their Con-straints on the Neoproterozoic Tectonic Evolution of South China
下江群沉积地质特征及其对华南 新元古代构造演化的约束

Middle Neoproterozoic geotectonic characteristics and proto-basin types in the western part of South China have aroused much controversy and are important implications for determining the position of the Yangtze Continent within the Rodinia configuration. The Xiajiang Group is developed between the Yanbian Group in the west characterized by strong deformation and high-grade metamorphism and the Banxi Group in the east with light deformation and low-grade metamorphism. It consists mainly of deep-sea turbidites and is regarded as a clue to finding the answer to the basic geological problems. 73 small-sized cross-beddings were measured, and the result suggests that the paleocurrent of the Xiajiang Group flowed westwards. A debris composition analysis of 33 sand-stone samples from the Qingshuijiang Formation in the middle part of the Xiajiang Group suggests that these clas-tic deposits were derived from a recycled orogenic belt. Geochemical features detected by the normal element analysis further indicate that the Xiajiang Group was developed in a retro-arc rift basin. Based on the above con-clusions in combination with the geotectonic features of the Yanbian Group and the Suxiong Formation, it is held that the western part of South China was a component part of an active continental margin during the deposition of the Xiajiang Group.