REMAGNETIZATION OF THE PYEONGAN SUPERGROUP IN THE YEONGWOL AREA, KOREA

Paleomagnetic and rock magnetic investigations have been carried out f or the late Carboniferous-Permian Pyeongan Supergroup, exposed in the Yeongwol area in eastern South Korea. A total of 228 independently ori ented core samples was drilled from thirteen sites for the study. The mean direction after bedding correction (D/I = 202.7 degrees/-24.6 deg rees, k = 2.4, alpha(95) = 36.9 degrees) is more dispersed than the in -situ mean direction (D/I = 175.3 degrees/-58.9 degrees, k = 69.0, alp ha(95) = 5.3 degrees), indicating that the fold test is negative at 95 % confidence level. In addition, the stepwise unfolding of the charact eristic remanent magnetization (ChRM) reveals a maximum value of k at 0% unfolding. Furthermore, authigenic magnetite and hematite grains ar e identified by the electron microscope observations. These results co llectively imply that the ChRM directions were acquired after tilting of the strata by a chemical remanent magnetization when the secondary authigenic magnetic minerals formed. The ChRM directions of the Superg roup, however, pass the reversal test at 95% confidence level suggesti ng that the remagnetization occurred during the period including both normal and reversed polarity intervals. Because the paleomagnetic pole position (39.4 degrees E, 85.6 degrees N, A(95) = 8.9 degrees) of the Pyeongan Supergroup calculated from the mean site directions of the C hRMs is close to that of the Tertiary period of the Korean Peninsula, it is interpreted that the remagnetization in this area occurred durin g the Tertiary. However, it is also plausible that the study area migh t be rotated about 30 degrees anticlockwise after the remagnetization at the end of the Daebo Orogeny, in the beginning of the Cretaceous pe riod.