REINTERPRETATION OF TECTONIC SITUATION OF KOREAN PENINSULA

Reinterpretation of tectonic situation of Korean peninsula (KP) revealed that the KP�Œs Moho depth of 25km in average is too shallow to have continent-continent collision, and that recent aeromagnetic satellite data combined with gravity anomaly (S. Maus et al, 2004), differential velocity of P wave (T. Hao et al, 2005), and basic volcanic occurrence (A. Ishiwatari et al, 2003) of the far east Asia support the detoured collision belt to the southwestern tip of KP rather than that of the extended Yangtze block, which crosses the KP and is bound by Imjingang fold belt (IFB) and Ogcheon fold belt (OFB).

Regional geological mapping data coupled with structural, petrological and geochronological data of IFB and OFB revealed that: (1) IFB does not cross the KP, but curves to the northeastern KP. Meanwhile OFB curves to the east sea. Therefore they are not convergent such as two limbs of F1-fold to satisfy the indentation model (Yin and Nie, 1993). Contrarily they are divergent. (2) IFB and OFB do not correlate stratigraphic sequence. (3) High P-T minerals characterizing the collision belt have not been found in the IFB or OFB. However, muscovite of 226 Ma (Kim et al., 2000), amphibolite faces of 255 - 240 Ma (Lee & Cho., 1995), omphacite inclusion in garnet of 230 - 300 Ma (Oh et al., 2002) are occurred not only along the IFB but also between IFB and OFB, (4) CHIME (Chemical Th-U-total Pb Isochron Method) and Sm-Nd data indicated thermal event of 250 Ma was not restricted to the IFB or OFB, but throughout the KP (Adachi etal, 1998). (5) SHRIMP data (Cho, 2005) suggested the sediments of OFB constrain to 400-450 Ma. (6) Sedimentation age of OFB's pebble was measured to c. 370 Ma by CHIME (K. Suzuki et al, 2005). The results of the above studies do not support the previous tectonic models of crossing the KP, but do support a detour model.

The northern boundary of the Tertiary Gunsan basin in Yellow Sea is coincident to the eastern extension of the Sulu belt and faces the NNW-fault (T. Hao etal, 2005) at the eastern edge of Yellow Sea, which is close to the western KP. If considering c. 100-km shortening of OFB with dextral shear sense, the possible footpath should detour the KP around the southwestern tip of KP, the Jeju Is. The final destination would be the southwestern Japanese Island Arc.