One hadean zircon from the Cambrian sandstone in the southern part of South China has a U-Pb age of 4107±29 Ma with ε Hf(t) value similar to that of the homochronous depleted mantle and Hf model age of 4102±21 Ma.This demonstrates the existence of hadean crustal remnant in South China.A close match between the U-Pb age and Hf model age with the highly position ε Hf(t) value indicates the growth and immediate reworking of juvenile crust from the depleted mantle at ca 4.1 Ga.The prominent "Pan-African" and Grenville zircons derived from the exotic sources were also found in the sample,which indicates a linking between South China and Gondwana in the Cambrian period.The southern part of South China has complex histories of crustal growth and tectonic evolution.
We analyzed the major and rare earth element compositions of siliceous deposits from the Upper Devonian Liujiang Formation,Lower Carboniferous Luzhai Formation,Lower-Middle Permian Sidazhai Formation and Tapi Formation,which are widely distributed as bedded cherts in the interplatform basinal successions of the Youjiang Basin.The Liujiang Formation and Luzhai Formation cherts generally have high Al/(Al+Fe+Mn) values(0.38-0.94) and are non-hydrothermal cherts.These cherts are generally characterized by moderately negative Ce anomalies and high Y/Ho values relatived to PAAS,indicating that the Youjiang Basin might have evolved into an open rift basin during the Late Devonian-Early Carboniferous.The Sidazhai Formation cherts from Ziyun generally have high Al/(Al+Fe+Mn) values(0.60-0.78),suggesting negligible contribution from a hydrothermal component.The Sidazhai Formation cherts from Hechi and the Tapi Formation cherts from Malipo generally have low Al/(Al+Fe+Mn) values(0.09-0.41),indicating an intense hydrothermal input.Relatived to the Sidazhai Formation cherts,the Tapi Formation cherts have higher Ce/Ce*values(0.68±0.19) and lower Y/Ho values(41.83±13.27),which may be affected by the terrigenous input from the Vietnam Block.The Sidazhai Formation cherts from Ziyun and Hechi exhibit negative Ce anomalies(0.43±0.12,0.33±0.17,respectively) with high Y/Ho values(57.44±16.20,46.02±4.27,respectively),resembling the geochemical characteristics of open-ocean basin cherts.These cherts were deposited on a passive continental margin adjacent to the Babu branch ocean,which may have contributed to upwelling.Detailed spatial studies on geochemical characteristics of the Late Paleozoic cherts can unravel the evolution of the Youjiang Basin.
