Detrital Zircon Ages and Hf-Nd Isotopic Composition of Neoproterozoic Sedimentary Rocks in the Yangtze Block: Constraints on the Deposition Age and Provenance

The South China craton was formed by collision of the Yangtze and Cathaysia blocks during the Neoproterozoic Jiangnan orogeny (also termed the Jingnin or Sibao orogeny in Chinese literature). Basement rocks within the Yangtze block consist mainly of Proterozoic sediments of the Lengjiaxi and Banxi groups. U-Pb ages of detrital zircons obtained by the laser ablation inductively coupled plasma mass spectrometry dating technique imply that the deposition of the Lengjiaxi Group continued until the Neoproterozoic. The youngest detrital zircons suggest a minimum deposition age of similar to 830 Ma for the Lengjiaxi Group and an initial deposition age of 785 +/- 12 Ma for the Banxi Group, indicating a temporal hiatus of 48 +/- 13 Ma between these Neoproterozoic sedimentary rocks distributed in northwestern Hunan Province, South China craton. Detrital zircons from both the Lengjiaxi and Banxi groups have a wide range of epsilon(Hf) (t) values from -12 to 14.2 and a continuous Nd and Hf model age spectrum from similar to 820 Ma to 2200 Ma. Model ages of many detrital zircon grains reach up to ca. 2.9-3.5 Ga, indicating that both juvenile mantle material and ancient crust provided sedimentary detritus. This is also consistent with the Nd isotopic signature of sedimentary rocks recorded in the Lengjiaxi Group, suggesting a back-arc tectonic setting. The Banxi Group has slightly enriched Nd isotopic signatures relative to the Lengjiaxi Group, implying a higher percentage of old continental material in the sedimentary source. Combined with previously published data, new results help us to reconstruct the Neoproterozoic tectonic evolution of the South China craton.