Paleomagnetic Investigation of the Late Carboniferous-Early Triassic Sedimentary Rocks in the Yeongnam Massif, Korea

A paleomagnetic study has been conducted for the Upper Carboniferous-Lower Triassic Pyeongan Supergroup exposed in the Danyang area on the Yeongnam Massif, Korea to provide a clue to local and regional tectonic problems in Korea. Among the total of 475 samples from 41 sites of five formations, the characteristic remanent magnetization (ChRM) components were obtained from 263 samples (31 sites) of three formations (the Late Carboniferous Manhang Formation, the Early Permian Jangseong Formation and the Earth Triassic Donggo Formation). Tilt tests and reversal test in this study reveal that the ChRM of the Manhang and Donggo formations are primary in origin while the Jangseong Formation was completely remagnetized during the Early Tertiary. The Late Carboniferous and the Early Triassic paleomagnetic pole positions calculated from the site-mean directions of the primary magnetizations in this study are at 39.9°N, 2.2°E (A95 = 3.5°) and at 40.7°N, 17.8°E (A95 = 5.3°), respectively. These poles are close to the contemporary poles of the NCB rather than to those of the SCB, suggesting that the Yeongnam Massif has been connected to the NCB. Paleomagnetic paleolatitudes (1.5°N for the Manhang Formation; 10.2°N for the Donggo Formation) indicate that the Yeongnam Massif has moved northward from the proximate of the equator during Late Carboniferous-Early Triassic times. Paleomagnetic directional results in this study also yield an important interpretation on the local geologic problem in the northern part of the Yeongnam Massif. The Pyeongan Supergroup distributed in the Danyang area and the Taebaek area (Baekunsan Syncline) forms a curved geometry (e.g., arcuate belt). The paleomagnetic declinations of the primary remanences in the Danyang area are rotated counter-clockwise by about 50-60° from those in the Taebaek area. The change in the paleomagnetic declination correlates closely with the variation in structural trend (i.e., strike of the strata) between two areas. This result suggests that the curvature is a secondary feature due to relative vertical-axis rotation between the Danyang and Taebaek areas from the originally straight configuration.