New understanding of the tectonic evolution of the northern margin of Yangtze Block: Constraints from the geochronology and geochemistry of the Huashan Group

The Huashan Group, distributed in the Dahongshan area on the northern margin of the Yangtze Block that adjoining the South Qinling, is an important carrier to study the tectonic evolution of the Yangtze Block and South Qinling. Long-standing debates persist on the material composition, depositional ages and tectonic nature of the Huashan Group. In this study, the Huashan Group were dismembered into the Huashan tectonic mélange and the Huashan Group that with normal volcanic-sedimentary stratigraphy, and their tectonic natures were discussed separately. Depositional age of the Huashan Group has been redefined here, geochemical features of the basalt from the Huashan Group with the controversy of the tectonic background and zircon U-Pb dating of the tectonic mélange with the controversy of the age are studied. A synthesis of geochronological, geochemical, and sedimentological study results indicate that the Huashan Group was deposited during ca. 830–800 Ma and in an intracontinental rift basin which resulted from the breakup of the Rodinia supercontinent. The Huashan tectonic mélange belt may not a product constrained just by the Jinning orogeny, but a complex suture zone with multistage sources and tectonic superposition. Combining the existing study achievements, we propose a new understanding on the tectonic evolution of the Yangtze Block and the South Qinling during the Neoproterozoic to the Early Paleozoic.