A synthesis of Cretaceous palaeomagnetic data from South Korea: Tectonic implications in East Asia

Tectonic provinces in South Korea include the Precambrian Gyeonggi Massif, Palaeozoic Okcheon Belt, Precambrian Yeongnam Massif and Cretaceous Gyeongsang Basin, from northwest to southeast. The Cretaceous strata mainly occur in the Gyeongsang Basin as well as in several small basins along the boundaries of the Okcheon Belt and on the Gyeonggi Massif. This paper reviews and analyses previously published palaeomagnetic data from the Cretaceous successions in South Korea. A total of 23 Cretaceous palaeomagnetic poles, from 18 studies, satisfy more than four standard reliability criteria. The palaeomagnetic pole positions, from the Gyeongsang Basin and from small basins in the Gyeonggi Massif and the Okcheon Belt, are consistent with one another, indicating that the Korean Peninsula has been a single terrane since the Cretaceous. However, based on the comparison of the palaeomagnetic pole positions and the palaeolatitudes of blocks in the Gyeongsang Basin, it was observed that the Gyeongsang Basin had experienced tectonic adjustments during the Cretaceous Period. Within the Gyeongsang Basin, the geographically northern area (Yeongyang block) was rotated counterclockwise by 16.3° ± 4.6° with respect to the southern area (Milyang and Uiseong blocks), based on the comparison of palaeomagnetic pole positions between the two areas. This palaeomagnetic result and some geological features in the Gyeongsang Basin collectively indicate that the Yeongyang block underwent counterclockwise rotations, accompanied by northwestward protrusion, into the Yeongnam Massif during the Late Cretaceous. These relative tectonic movements within the Gyeongsang Basin were probably due to the northwestward subduction of the proto-Pacific oceanic plate during the Late Cretaceous. The gradual eastward displacement of the Korea's Cretaceous palaeopoles, from the Eurasian pole, increases with stratigraphic age, indicating that the Korean Peninsula underwent progressive clockwise rotations, with respect to Eurasia, during the Cretaceous Period. The clockwise rotation of Southwest Japan, with respect to Eurasia, is ascribed to the Miocene opening of the East Sea, and has no connection with the Cretaceous clockwise rotations of the Korean Peninsula, indicating that the Korean Peninsula and Southwest Japan may have been independent terranes during the Cretaceous Period.