EARLY AND LATE MESOPROTEROZOIC MAGMATISM, EARLY NEOPROTEROZOIC EXTENSION AND MIDDLE NEOPROTEROZOIC GLACIATION FOUND IN THE NORTHEASTERN OKCHEON METAMORPHIC BELT

It is believed that deciphering formation of the long-controversial Okcheon Metamorphic Belt (OMB) in central South Korea will play a key role in studying the crustal evolution of the Korean Peninsula and its surrounding regions. The Seochangni Formation distributed over the northeastern OMB overlies the Paleoproterozoic Busan Gneiss Complex and in contact with the Cambro-Ordovician Joseon Supergroup to the east. The detrital zircons of the Seochangni Formation mainly displays bimodal U-Pb age distribution of Mesoproterozoic with prominent peaks at ca. 1200 Ma and 1600 Ma. Although Early and Late Mesoproterozoic magmatism, as found in detrital zircons, has been unknown in South Korea until now, such age distribution characteristics are very similar to the Neoproterozoic Penglai and Tumon Groups located along the southern margin of the North China Craton and the Sangwon System of North Korea (Hu et al., 2012), both of which are overlain by Cambro-Ordovician strata. The similarity of the age distribution of the detrital zircons and the common distribution of the Cambro-Ordovician sedimentary basin in the adjacent area suggest that these three regions have undergone crustal evolution together as parts of the Sino-Korean Craton (SKC) since Paleoproterozoic. Therefore, we suggest that the hypothesis that the Early Triassic continental collision boundary between North China and South China Cratons extends eastward across the Korean Peninsula is not appropriate.

The northeastern OMB provides additional constraints on the Neoproterozoic evolution of SKC. A-1 type magmatism of about 860 Ma in the Gyemyeongsan Formation of the northeastern OMB, is likely to indicate the earliest extension within the Rodinia Supercontinent. Sr, C and O isotopic compositions of the Hyangsanni Dolomite of the northeastern OMB suggest its deposition around Sturtian glacial age (ca. 720-740 Ma). The presence of Neoproterozoic glaciation in SKC is further supported by the appearance of diamictite deposits in adjacent Hwanggangni Formation. Although stratigraphic problems have not yet been solved unambiguously, further studies on OMB are important to reveal the evolution of SKC, including several important issues such as Mesoproterozoic magmatism, Rodinia breakup, and Neoproterozoic glaciation.

Hu et al. (2012) Gondwana Research, 22, 828-842.