Paleomagnetic evidence for local oroclinal bending in the eastern Korean Peninsula

Abstract

A paleomagnetic investigation has been carried out for the Lower Triassic Donggo Formation exposed in the Danyang area on the Yeongnam Massif to constrain local and regional tectonic history of the Taebaeksan Zone, Korean Peninsula. Among a total of 201 samples from 18 sites of the Donggo Formation, the characteristic remanent magnetization (ChRM) components were obtained from 166 samples. Field tests such as tilt test and reversal test reveal that the ChRM of the Donggo Formation is of primary in origin. The Early Triassic paleomagnetic pole position calculated from the site-mean directions of the primary magnetization is at 40.7 degrees N, 17.8 degrees E (A(95) = 5.3 degrees). Comparison of the reliable paleomagnetic poles from the Danyang (this study), Taebaek, and Yemi areas in the Taebaeksan Zone reveals a regional division of the pole position, indicating the clockwise vertical-axis rotation of the Taebaek area by 47.2 +/- 11.1 degrees with respect to the Danyang and Yemi areas after the formation of the Pyeongan Supergroup. In addition, there is a significant relation between strike deviations and declination deviations with some flattening of the regression line in the southern Taebaeksan Zone. Thus, it is interpreted that the Pyeongan Supergroup in this region had a primary curvature at the timing of sedimentation and subsequently experienced post-Early Triassic oroclinal bending of approximately 47 degrees.