LA-ICP-MS U-Pb dating and Hf isotopes of detrital zircon grains from siltstone of Danzhou Group in northern Guangxi and their geological significance

This paper reports LA-ICP-MS U-Pb dating and Hf isotopes for detrital zircon grains of siltstone from Gongdong For-mation at the top of the Danzhou Group. The majority of zircon grains are transparent, euhedral and prismatic crystals with oscillato-ry zoning in CL images and have high Th/U ratios of 0.2~2.4, indicating an igneous origin for the zircon. The ²⁰⁶Pb/²³⁸Pb age distri-butions for the detrital zircon grains mainly range from 730Ma to 769Ma and 771Ma to 850Ma, and ε_Hf(t)and two-stage Hf model ages (T_DM2) range from -18.4 to 11.4 and from 1020Ma to 2812Ma, respectively. Moreover, there are some detrital zircon grains with relatively older ages with ²⁰⁶Pb/²³⁸Pb ages from 1910Ma to 3140Ma, and ε_Hf(t)and T_DM2 from -13.6~3.4 and 2740~3635Ma, respec-tively. Combined with previous researches, the authors infer that the maximum depositional age of the Gongdong Formation from Danzhou Group is 706±10Ma. The source region was predominated by Neoproterozoic magmatic rocks from Yangtze Block (ca. 750~830Ma) with the mixture of minor Archean magmatic rocks. There was developed the Greenville movement in South China re-sulting from the assembly of Rodinia supercontinent. In addition, on the basis of the ε_Hf(t)and T_DM2 data of the detrital zircon grains, the authors hold the existence of three stages for the crust growth in the study area:① 3.64Ga to 3.25Ga, with the juvenile crust at 3.64Ga; ② 2.98Ga to 2.37Ga; ③ 2.19Ga to 1.28Ga.