Thermal histories of the Cretaceous Pungam and Yeongdong basins, Korea based on apatite and zircon fission track analysis

Abstract

Apatite and zircon fission track (FT) analyses were carried out to reconstruct the thermal histories of the Cretaceous Pungam and Yeongdong basins, Korea. These basins were formed along the sinistral strike-slip faults in the Early Cretaceous and were compressed in the Late Cretaceous by transpressional stresses due to the change in subduction direction of the Kula/Pacific Plate. In the Pungam and Yeongdong basins, apatite samples have consistent FT ages of ca. 50 Ma and ca. 63 Ma, respectively, much younger than their stratigraphic ages. In contrast, the zircon FT ages of both basins show relatively wide ranges, i.e., from 89 to 70 Ma in the Pungam Basin, and from 83 to 64 Ma in the Yeongdong Basin. Zircon single-grain age spectra also show multiple age populations. Co-existence of both the older and younger FT ages in comparison to the depositional age (Pungam Basin: ∼70 Ma, Yeongdong Basin: ∼100 Ma) indicates that the zircon samples from both basins were partially annealed. The Pungam Basin was heated into the zircon partial annealing zone (ZPAZ) by burial, volcanic activity and associated hydrothermal fluid, then cooled below the apatite closure temperature atca. 50 Ma. The Yeongdong Basin was also heated into the ZPAZ after deposition by burial and volcanic activity, then cooled down below the apatite closure temperature atca. 63 Ma, and was uplifted to the present surface. Comparing these data with those of the Gyeongsang Basin, the response to transpressional stresses seems not to be controlled by the distance of the basin from the active continental margin. Further studies are needed to clarify such tectonic inversion of the sedimentary basins in the active continental margin.