Geochronology and sedimentology of the Huashan Group in the northern Yangtze Block: implications for the initial breakup of the South China
Middle Neoproterozoic sedimentary sequences are widespread in South China and provide crucial insights into the geological evolution of sedimentary basins related to the breakup of the Rodinia supercontinent. The Huashan Group is a key Neoproterozoic stratigraphic unit in the northern Yangtze Block, South China; however, its depositional age and tectonic setting of deposition are debated. Here, we report zircon U–Pb geochronology and Hf isotope data for a tuff from the second section of the Hongshansi Formation near the bottom of the Huashan Group. Zircon U–Pb geochronology yields a 206Pb/208U age of 836 ± 4 Ma (MSWD = 0.74, n = 29). Zircon Hf isotope ratios have εHf(t) values of + 3.1 to + 5.4 and TDM2 ages range from ca. 1.5 to 1.4 Ga, which indicates that juvenile materials derived from the mantle were involved in their host magmas. Combined with previous research, the Huashan Group was deposited from ca. 830 to 800 Ma from bottom to top, and it contains alluvial fan, fan delta, and semideep to deep lacustrine facies, which represent early sedimentation into a continental rift basin. Rifting and basin formation began at ca. 830 Ma in South China, which is coeval with the initial breakup of the Adelaidean Rift in southeastern Australia. The Huashan Group was deposited during the first and the second episodes of a superplume associated with the breakup of the Rodinia supercontinent.