ND ISOTOPIC STUDY OF UPPER CAMBRIAN CONODONTS FROM KOREA AND IMPLICATIONS FOR EARLY PALEOZOIC PALEOGEOGRAPHY

The correlation of the Korean Peninsula with neighboring South and North China blocks has been one of the most important and long debating issues in East Asian tectonics. The eastward extension of the Chinese collisional belt between the South and North China blocks into the Korean Peninsula is still in dispute. The lower Paleozoic sedimentary rocks in South Korea, the Joseon Supergroup, accumulated in the Okcheon belt which has been proposed as the suture zone or the block boundary between the South and North China blocks. The Joseon Supergroup comprises five different litho-stratigraphic units, and has been proposed to be divided into two tectonic blocks by the Honam Shear Zone (HSZ) in the Okcheon belt; among them, the Yeongweol unit in the western part of the HSZ is correlated with South China and the Duwibong unit in the eastern part of the HSZ with North China. To test the above geodynamic interpretation, this study analyzed the Nd isotopic composition of Upper Cambrian conodonts from the Duwibong and Yeongweol units. The difference of the eNd (T) values between the two units is about 3e units. Compared to a wide range of the eNd (0) values in the modern oceanic basins, this slight difference can be regarded as a variation in a same paleo-watermass. The eNd (T) values of the two units are consistent with coeval values from the North China, and this suggest that the Duwibong and Yeongweol units shared same oceanic watermass with the North China. Considering the available early Paleozoic paleogeographic reconstructions, the Nd isotopic signatures of the North China, Duwibong and Yeongweol units are independent of Laurentia and Baltica and thus are indicative of an another unique oceanic watermass.

In contrast to the previous tectonic interpreations, the same paleoceanographic signatures of the Duwibong and Yeongweol units and North China and recent developments suggest that the Yeongweol unit is not correlated with South China but correlated with North China, and the Korean Peninsula and North China block may have been included in a larger continental block, the Sino-Korean block. The collisional belt between the South and North China blocks may not extend into the Korean Peninsula.