Structural style of the Okcheon fold-thrust belt in the Taebaeksan Zone, Korea

Structural interpretation of the distinct map pattern defined by highly connected thrust traces in the map view of the Taebaeksan Zone provides insight into the structural style of the northeastern Okcheon Belt. The map pattern can generally be explained by either a folded imbricate fan or a hinterland dipping duplex. The same geometry could also be formed by a complex combination of major imbricate thrusts and their connecting splays, having the structural architecture of a typical fold-thrust belt. However, a folded imbricate fan model is not adequate to explain the absence of late Paleozoic to early Mesozoic strata (i.e. the Pyeongan Supergroup) between two major thrusts (viz. the Pyeongchang and Machari thrusts) in this area. This result further suggests that the Yeongwol area, the western part of the Taebaeksan Zone, is a duplex that corresponds to a more internal and deeper hinterland part of the fold-thrust belt, while the imbricate thrusts with low connectivity in the Taebaek area, the eastern part of the Taebaeksan Zone, indicate a more external and shallower foreland portion of the belt. In addition, cross-cutting relations and newly obtained sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages from a cross-cutting dike and syntectonic sedimentary rocks suggest limited thrust reactivation after the early Jurassic and early Tertiary, respectively. In spite of this, the original geometry of the fold-thrust wedge in the Taebaeksan Zone remained well preserved.