K–Ar illite dating to constrain multiple events in shallow crustal rocks: Implications for the Late Phanerozoic evolution of NE Asia

• Published in: Journal of Asian earth sciences Vol. 95; pp. 313 - 322
• Main Authors: Song, Yungoo, Chung, Donghoon, Choi, Sung-Ja, Kang, Il-Mo, Park, Changyun, Itaya, Tetsumaru, Yi, Keewook
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-12-2014
• Subjects: Chugaryeong fault; Fault clay; Illite polytype; K–Ar age-dating; Multiple events; Multiple events; Illite polytype; Chugaryeong fault; K–Ar age-dating; Fault clay
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2014.05.018

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•Determination of fault timings using K–Ar dating and illite-age-analysis for fault clays.•Multiple events during upper Cretaceous to Paleogene in Chugaryeong fault belt.•Recognition of high-T hydrothermal origin 2M1 illite in fault clays.•Tectonic evolution of the Korean Peninsula since Late Cretaceous.
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.