CURVED EXTENSION OF CHINESE COLLISION BELT IN KOREAN PENINSULA: THE IMJINGANG FOLD BELT

Geological mapping data coupled with structural, petrologic and geochronological data on Imjingang fold belt (IFB) along demilitarized zone (DMZ) in the central Korean peninsula have revealed as follows. (1) IFB does not cross Korean peninsula to the east but has curved to the north. (2) Ultrahigh pressure minerals such as coesite or diamond characterizing Dabie-Sulu metamorphic rocks in China have not been found from metamorphic rocks of IFB. (3) Chemical Th-U-total Pb Isochron Method (CHIME), Sm-Nd and K-Ar age data show that thermal event of ca. 250 Ma took place extensively in Korean peninsula. (4) Distribution of the Upper Devonian to Lower Carboniferous Imjin System is narrower than that has been thought and is restricted to the western part of IFB. (5) Haeju-Wonsan fault (HWFT), the northern boundary of IFB, is an important tectonic line of dividing basements of Korean peninsula. (6) The Proterozoic Yeoncheon Group is restricted within IFB and has been effected by ductile shearing. Results of this study do not support the previous tectonic models that IFB crosses Korean peninsula as an eastern extension of Quinling-Dabie-Sulu collision belt in China and that North China Block has been indented by South China Block along IFB and Ogcheon Fold Belt (OFB). Therefore, to better understand the tectonic evolution of East Asia, a re-examination of IFB itself as well as OFB in Korean peninsula is necessary.