The Okdong Fault

옥동단층(玉洞斷層)

The Okdong Fault is situated in Okdong-Hamchang area, the central part of Korea. The area consists of Precambrian gneisses and granitoids, Paleozoic clastic and carbonate rocks, and Mesozoic clastic rocks and igneous intrusives. The Okdong Fault is situated along contact boundary between the lowermost Cambrian Basal Quartzite and Precambrian basements. Mylonites occur as narrow zone which is extended over 100km and is restricted to within 10m-30m along the Okdong Fault. The main features of mylonites are quartz mylonite derived from Cambrian Basal Quartzite and mylonitic granitoids from Precambrian granitoids. Movement sense is deduced as a sinistral strike-slip movement with evidence of rotation of sheared porphyroclasts, rotation of fragments and S/C-bands. The mylonite zone has been reactivated as fault which reveals oblique-slip movement. The fault resurges as faults which reveals normal(to the NW) and reverse(to the SE) dip-slip movement. Normal faults are dominant in the northern and southern part and reverse or thrust faults are dominant in the central part of the Okdong Fault. The thrust movement can be correlated with the Daebo Orogeny of Jurassic Period. Granites and dyke rocks intruded into Paleozoic and Precambrian rocks during Cretaceous Period.