Paleomagnetic results of the Late Permian Gobangsan Formation, Korean Peninsula: Remagnetization in the southeastern periphery of the Bagjisan Syncline

Abstract

Sedimentary rocks in the Late Permian Gobangsan Formation were collected at 7 sites for paleomagnetic study in the southeastern periphery of the Bagjisan Syncline, Korean Peninsula. The Gobangsan Formation revealed a stable secondary magnetization component with unblocking temperatures of 500-580• C and 650• C from two sites, while the other sites possessed only a present day viscous remanence. The secondary component resides in magnetite and hematite. The site-mean directions of the two sites before tilt correction (D = 355.9• , I = 50.2• with α 95 = 4.3• and D = 355.7• , I = 53.3• with α 95 = 6.1 • ) suggest that the remagnetization occurred after Early Cretaceous. The most plausible mechanism of the remagnetization is considered to be a chemical authigenesis because the other possible mechanisms of the remagnetization such as thermoviscous process and Recent weathering can be ruled out by rock magnetic experiments. The timing of the remagnetization is constrained during Tertiary time, because the observed directions are distinguishable from the Cretaceous directions and because Recent remagnetization is unlikely. This is ascertained by good agreement between the observed and the Tertiary directions.

Clockwise rotation of the Korean Peninsula with respect to the North China Block inferred from an improved Early Triassic palaeomagnetic pole for the Ryeongnam Block

“…Eight to nine hand samples were distributed over distances ranging up to 15 m in each site and were orientated by magnetic compass. Sites NF1, 2, 3 and 4 correspond to the sites SK8, 9, 28 and 27 in Uno (1999), respectively, and were restricted to this area because almost complete remagnetization has been found elsewhere in this area (Uno 1999, 2000). The present geomagnetic field declination was calculated using the International Geomagnetic Reference Field (IAGA Division V, Working Group 8 1995).…”