THERMAL HISTORIES OF CRETACEOUS BASINS IN KOREA: RESPONSE OF THE EAST ASIAN CONTINENTAL MARGIN DUE TO SUBDUCTION OF THE PALEO-PACIFIC PLATE

To reconstruct the general thermal history of the Cretaceous basins in Korea focusing on their uplift in response to tectonism occurred at an active continental margin, apatite fission track and illite crystallinity analyses were carried out on the sediments of the Cretaceous Jinan Basin, southwestern Korea. The Jinan Basin was formed along the sinistral strike-slip fault in the Early Cretaceous and was compressed in the Late Cretaceous by transpressional stresses due to the change of subduction direction of the Paleo-Pacific (Izanagi) Plate. Illite crystallinity analytical results of the Jinan Basin sediments suggest the maximum burial paleotemperature as ca. 200℃, while their apatite fission track results show consistent fission track ages of ca. 68 Ma, indicating total resetting of the fission track ages by burial. Detailed FT length modeling results suggest two-stage cooling events of the Jinan Basin sediment to occur during ca. 95-80 Ma and after ca. 30 Ma with a quiescence period between them. The cooling rate of the Jinan Basin sediments during 95-80 Ma was ca.7.3℃/Ma, with a corresponding uplift rate of ca. 0.21 mm/yr. Compilation of thermal histories of Cretaceous basins in Korea indicates that uplifting was the main cause of their cooling between ca. 95 and 80 Ma with slightly earlier uplifting of the strike-slip basins by transpressional force due to the change of the subduction direction of the Izanagi Plate. Comparison of these results with thermal history of the accretionary prisms in southwestern Japan suggests that the subduction of the Izanagi-Pacific ridge during the Late Cretaceous facilitated the regional uplift of the East Asian continental margin.