Electron Spin Resonance (ESR) Dating of Pre-Quaternary Faults in the Sichuan Basin, SW China

The electron spin resonance (ESR) dating method is thought to be limited to the Quaternary period. In this study, we attempt to expand the ESR dating range to the pre-Quaternary using three fault-zone samples collected from faults in the Sichuan basin and its surroundings. We adopt a gamma-ray radiation dose of up to 2 x 10(4) Gy, which is much greater than that typically employed, and find that the ESR intensity of the E-1' center (a type of signal for ESR dating) in quartz continuously increases with the gamma-ray dose and is slightly influenced by the radiation dose rate. This indicates the potential of ESR to date pre-Quaternary faults. By simulating environmental radiation under geological burial conditions, we use ESR to date the latest extension event in the western Hubei and Hunan thrust belt to 9.17 +/- 0.76 Ma and the thrusting of the Longmenshan fault zone toward the Sichuan basin to approximately 6.14 +/- 0.73 Ma. Conversely, the saturated ESR intensity of fault-zone samples from the Daba fault zone suggests a lack of strong tectonic activity in the southern Daba fault zone in the last 10 Ma. Our results are consistent with fission track ages and the regional tectonic evolution history. Therefore, ESR is a practical method for dating pre-Quaternary faults in structural and petroleum geology applications.