Abstract:

The chronology of the Changjie altered olivine pyroxenite of Tongdao area of western of Hunan province in Sanjiang fault is researched in this paper to discuss the emplacement age of rock, the deformation time of the fault and the response to the Pan-African event. Changjie altered olivine pyroxenite intruded into the Hetong formation of Danzhou group, which suffered intense chloritization, serpentinization and tremolite alteration. Microscopically, the late chlorite veinlets cut through the early altered minerals, showing the characteristics of multi-stage alteration and suggesting that they were affected by at least two tectonic thermal events after diagenesis. Zircon U-Pb dating results are concentrated at 441.0±11.0 Ma、546.5±8.5 Ma、774.3±3.9 Ma and 820-1000 Ma. 774.3±3.9 Ma is the youngest magmatic zircon age, which represents the formation age of the Changjie altered olivine pyroxenite. 820-1000 Ma is the age of captured zircons during magmatic emplacement. The hydrothermal zircon age of 441.0±11.0 Ma is consistent with the formation age of the regional NNE trending fault, which represents the active age of the Sanjiang fault. The age of 546.5±8.5 Ma is also hydrothermal zircon age, which is consistent with the age of Pan-African tectonothermal event, indicating that the research area was influenced by Pan-African tectonic thermal event.

Key words: hydrothermal zircon, deformation age, Pan-African tectonic events, Sanjiang fault zone, adjacent areas of Hunan and Guangxi