GEOCHRONOLOGICAL IMPLICATION OF K-Ar, FT AND TL SYSTEMS OF FAULT GOUGE FROM YI-SHU FAULT ZONE
Chen Wen-ji, Ji Feng-ju, Li Qi, Li Da-ming, Wang Qing-long and Wang Xin(Institute of Geology, State Seismological Bureau)
The ages of 1Md illite (1μ size fraction), quartz(2-10μ size fraction), and apatite in fault gouge from Yi-Shu fault zone were determined by K-Ar, TL and FT techniques, separately. Three distinct episodes of fauting as represented by the gradual decrease of temperature-sensitivity of TL, FT and K-Ar systems have been recognized. The K-Ar ages(90-110Ma) are obtained from seven IMd illites considered to represent the best approximation of the earliest strong activity of the fault zone as the same as geological evidence. They can be further divided into two stages, i. e. 110Ma for the eastern Fault(F1), and 90-95 Ma for the western Fault (F2, F3 and F4). The FT ages (30-56Ma) of four apatite samples probably represent the second episode of strong activity of the fault zone, while the TL ages (40-50Ka) of five quartz samples may represent the latest episode.It is suggested that the K-Ar, FT and TL separate dating of 1Md illite, apatite and quartz from fault gouge can be used to reveal the development history of faulting, including time and intensity.