NW-SE trend of the Orcheon Orogen: evidence for NE-SW shortening

Abstract

The fragility of structures in rocks that have been multiply deformed commonly results in geometries that are too complex, or sometimes too simple, to readily allow a structural geologist to reconstruct the complete deformation history of a rock. Complexities are commonly overlooked, or ignored because they are attributed to heterogenieties in the flow field. Presence of NW-SE-trending structures has previously been recognized by several researchers at different places in the NE-SW-trending Ogcheon Orogen (Fig. 1; Reedman et al., 1973; Cluzel et al., 1991; Ihm and Chang, 1993; Koh and Kim, 1995). It has been considered that these structures have resulted from the development of heterogeneous strain, such as sheath-like folding (e.g. Cluzel et al., 1991) or a convergent shear flow resulting in oblique fold (Koh and Kim, 1995) during a series of progressive NW-SE bulk shortening events. However, recent palaeomagnetic work on the Ogcheon Supergroup (Lee et al., 1997) suggests that there was NE-SW directed tectonism in East Asia (e.g. Liu, 1993; Yin and Nie, 1993). Plus, Lee (1999) has documented NW-SE-trending structures appearing in some places at variable scales in the Ogcheon Orogen and reassesses the tectonic history of the Ogcheon Orogen.