LIAO Zhen1,2,3, LIU Yu-ping1, LI Zheng-xiang4, YE Lin1, LI Chao-yang1,5, WANG Da-peng1
1. State Key Labortory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China;
3. China Non-ferrous Metal Resource Geological Survey, Beijing 100012, China;
4. Department of Applied Geology, Curtin University of Sciences and Technology, Bentley, WA6102, Australia;
5. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 430026, China
Abstract: The Yaoshan Group locates in the southeastern Ailao Shan-Red River strike-slip fault zone. It has experienced high-amphibolite facie metamorphism and chorismitization, thus it was thought as the Precambrian basement of the South China block in SE Yunnan region. In order to determine the ages of the protolithos, later magmatic, metamorphic and tectonic events of the Yaoshan Group, the zircon SHRIMP U-Pb dating was investigated. According to CL images and optical microscope analyses, the zircons derived from the Yaoshan Group, which are very complicated with the metamorphosed re-crystal and over-growthing, could be divided into inherited, metamorphic, anatectic or magmatic types. Besides a few analyzed spots with the Neo-Proterozic ages, the inherited zircons mainly yielded 206Pb/238U ages in the range from 235±1.7 Ma to 261±3.6 Ma, with a weighted mean value of 250.8±9.8 Ma (N=4, MSWD=4.1). The 206Pb/238U ages of anatectic or magamatic zircons represented by two peaks of ~85 Ma and ~75 Ma, respectively. The 206Pb/238U ages of metamorphic zircons are in the range from 49 Ma to 30 Ma, with three peaks of 32, 37 and 42 Ma, respectively. Based on the regional geology, this study suggested that the peak age of inherited zircons (250.8±9.8 Ma) indicated that the major protolithos of the Yaoshan Group might be formed later than the Permian, and that metamorphic, anatectic/magmatic zircons showed five 206Pb/238U peak ages of ~85 Ma, ~75 Ma, ~43 Ma, ~37 Ma and ~32 Ma might indicate five important tectonic, magmatic and metamorphic events in the south part of Red River fault since the later Yanshannian.
Keywords: Yaoshan Group zircon SHRIMP geochronology protolithos magmtic-metamorphic-tectonic events Red River fault zone southeastern Yunnan
