DETRITAL ZIRCON GEOCHRONOLOGY OF RIVER SEDIMENTS IN SOUTH KOREA AND ITS IMPLICATIONS FOR EAST ASIAN TECTONICS

The collision between the North and South China blocks has started in the Early Triassic, and its eastward extension is important to understand a tectonic history of the East Asian continent. The Korean Peninsula is located in the East Asian continental margin and mainly comprises three Precambrian massifs and two metamorphic belts in between them. It is still controversial whether or not the collision belt passes through the Korean Peninsula. Various hypotheses have been suggested for decades. Among the three Precambrian massifs, the tectonic affinity of the Gyeonggi massif in the middle of the peninsula is under hot debate: whether it belongs to North China Block or to South China Block. To contribute for this discussion, we carried out U-Pb analysis of detrital zircon grains from major river-mouth sediments draining the two Precambrian massifs (Gyeonggi and Yeongnam massifs) in South Korea, using a LA-ICP-MS. We obtained 518 concordant (discordance < 15%) zircon ages ranging from ca. 3566 Ma to ca. 48 Ma. Regardless of river-mouth location, predominance of Mesozoic (249 – 79 Ma) and Paleoproterozoic (2491 – 1691 Ma) ages indicates that the zircon ages reflect present exposures of plutonic/metamorphic rocks in the drainage areas of the Korean rivers. Considering the Triassic being the Chinese collision timing, comparison of pre-Mesozoic detrital zircon-age data between the North and South Korean river sediments reveals that the both age distributions are identical, characterized by a strong Paleoproterozoic (~1.9 Ga) peak and a subordinate Archean (~2.5 Ga) peak. This result suggests that the three Precambrian massifs record the same pre-Mesozoic magmatic history. Thus the eastward extension of the Chinese collision belt into the Korean Peninsula seems questionable.