GEOMETRIC CONSTRAINT OF SO-CALLED COLLISIONAL IMJIN BELT ALONG DMZ, KOREA

Collisional belt retained the effects of eastward extension from Chinese Sulu belt is increasingly being buoyant, especially in Korea. Neighboring regions generally lack evidence of coeval arc volcanism or plutonism around 250 Ma. Following the consumption of intervening continent-continent lithospheres, no ultra-high pressure (UHP) orogen marks the demilitarized zone (DMZ), mid-Korea, of astonishingly high promontory. An isolated Paleozoic metasediment basin, Yeoncheon Group, showing sinistral normal shear sense and indicating detrital SHRIMP U-Pb zircon core age of protolith of paragneiss from 447.0±4.4 Ma to 396.7±6.1 Ma (Cho, etal, 2005), in the central part of ENE-trending DMZ region had high peak metamorphism at around 250 Ma, which is equivalent to CHIME zircon age of the whole Precambrian basement of Korean peninsula and Japanese Hida belt (Suzuki & Adachi, 1994; Chwae, 1998; Suzuki etal, 2006). Chinese collisional Quinling-Dabie-Sulu belt is generally ca 30 to 20 Ma younger than those of eastward regions, Korean peninsula and Hida belt, which metamorphism grade to middle to low. It reveals the 250 Ma middle-grade metamorphism model does not typify the DMZ region, called to Imjingang fold belt (IFB), nor to certain region, for instance Ogcheon belt of Korea and Hida belt, as indicator of collisional belt. If considering Precambrian basement's quartzite trace along the mid-western DMZ region as a key marker, the formline shows F₂-fold, bearing northwards plunge and mineral elongation, and being intruded by meta-syenite, showing dextral normal shear sense, along ENE-trend-F₁-fold axial trace. A so-called collisional fault (Imjingang fault), as a southern limit of the IFB, also strikes along the F₁-fold axis with development of the Upper Triassic to Lower Jurassic coal-bearing sediment basins, which are fault-bound, intermittently continuous each other, and partly affected by right-lateral strike-slip shear movement. The above, evidently showing connected and regional F₁/F₂-fold geometry between the IFB and the adjacent Proterozoic basement, is hard to launch a continent-continent collision concept along the IFB either or at the Imjingang fault. The IFB may be a Paleozoic fault-bound basin within the Mid-Proterozoic basement, Gyeonggi massif.