Abstract: A set of epimetamorphic marine volcano-sedimentary rock series developed in Tuolugou cobalt (gold) mining area, Qinghai Province, of which the formation ages and tectonic attributes are controversial. In this paper, zircon LA-ICP-MS dating, Lu-Hf isotopic and geochemical analysis were carried out on the phyllites from Tuolugou deposit, and their protolith depositional ages, sediment provenance and tectonic affinity of the basement were discussed. The chronological results show that the youngest age group of detrital zircons is 433-412 Ma with weighted average age of (422.8±6.8)Ma. Combined with the data of regional tectonic magmatic events, the upper limit of the protolithic depositional age is the Late Silurian. Theε_Hf(t) values of zircons in age group of 433-412 Ma range from －2.02 to 5.47, with an average of 1.80, indicating that the parent rocks of this zircon group are mainly new crustal materials. The T_DM1 age ranges from 1 124 to 829 Ma, indicating that the zircons originated from the crust mantle interaction during the convergence of the Rodinia supercontinent in the Grenvillian period. The petrogeochemical results show that the protolites of the Tuolugou phyllites may be a set of mud-sandy sedimentary rocks, and the depositional environment is a stable passive continental margin. It is consistent with the result of regional tectonic evolution which is: The subduction of the middle Kunlun Ocean ended around 430 Ma, and the whole east Kunlun area began to enter the intraplate extension setting, while the southern part of the south Kunlun block entered the passive continental margin in the Late Silurian. The comprehensive analysis of the U-Pb age spectrum of detrital zircons shows that the original properties of detrital zircons during the Archean is not clear, and the basement of the south Kunlun in the Mesoproterozoic has obvious affinity with the South China craton. Since the Grenvillian orogeny formed the United Continent of Cathaysia-Yangzi-Kunlun-Qaidam-Qilian, the Kunlun block may have been separated from the United Continent during the Pan-African period (about 650-550 Ma)

Key words: East Kunlun, Tuolugou cobalt (gold) deposit, phyllite; detrital zircon chronology, Lu-Hf isotopes, geology significance