A recently developed illite-age-analysis (IAA) approach was applied to determine the multiple events for the Chugaryeong fault belt, Korea. Each event was determined by a combined approach of the optimized illite-polytype quantification and the K-Ar age-dating of clay fractions separated from the fault clays. The Late Cretaceous to Paleogene events (76.5±0.8, 69.1±0.6, 59.3±0.7, and 48.2±0.7Ma) were recognized by calculating the authigenic 1M/1Md illite ages on the IAA plots of the fault clays. The Early Cretaceous ages (121.7-124.7 and 112.4±1.5Ma) were also obtained from the convergent intercepts of 100% 2M1 illite on the IAA plots. The absence of the 2M1 illites in the host-rock indicates that the Early Cretaceous ages represent the timings of high-T hydrothermal events of >280°C. The 2M1 illites in the fault clays should be pre-formed by a fluid-rock interaction under a relatively high-T subsurface condition, and be mechanically reworked into the near surface along the fault by post-tectonic events. This is the first report determining the absolute age constraints of multi-activated tectonic events from a fault. These geochronological determinations of the multiple events recorded in the Chugaryeong fault belt are crucial to establish the tectonic evolution of the Korean Peninsula since the Late Cretaceous.
All Science Journal Classification (ASJC) codes
- Earth-Surface Processes