STRUCTURAL GEOMETRY AND KINEMATICS OF THE TAEBAEKSAN ZONE IN THE PYENGCHANG-YEONGWOL AREA, OKCHEON FOLD-THRUST BELT, KOREA

The Okcheon Belt in the south-central part of the Korean Peninsula is an overall NE-SW trending fold-thrust belt, consisting of the northeastern Taebaeksan Zone and the southwestern Okcheon Zone. It is bounded by the basements of the Precambrian Gyeonggi Massif to the north and the Precambrian Yeongnam Massif to the south. The Taebaeksan Zone consists mainly of the Cambrian to Ordovician Joseon Supergroup, Carboniferous to early Triassic Pyeongan Supergroup, and the subordinate early Jurassic Bansong Group. The Pyeongchang and Yeongwol areas of the western Taebaeksan zone preserved distinct map patterns of typical structures of the hinterland. We have conducted three-dimensional geometric interpretations, kinematic analyses and SHRIMP U-Pb zircon and K-Ar age-dating. The results show that (1) in the Pyeongchang area, older Precambrian basements are surrounded by the younger Precambrian cover rocks (viz. Bangrim group) along the thrust, forming geometry of klippe; (2) in the Yeongwol area, lower Paleozoic strata is overlain by the upper Paleozoic or Mesozoic strata along the N-S trending highly connected thrust traces in the map view, defining a Yeongwol thrust system. It can be interpreted by alternative duplex models in terms of a traditional hinterland dipping duplex vs. a hinterland dipping duplex formed by a combination of major thrusts with connecting splays; (3) SHRIMP U-Pb zircon ages from a dike and synorogenic sediments as well as K-Ar illite ages of fault gouges, together with previously reported evidence from the Yeongwol area, suggest polyphase tectonic events at least after the Permo-Triassic. These interpretations suggest that the Pyeongchang and Yeongwol areas of the Taebaeksan Zone may be well correlated to an internal and deeper hinterland portion, and are modified during later deformations to form present-day structural style of the Okcheon fold-thrust belt.